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diff --git a/README.markdown b/README.markdown index 3223a2bd..77e09abd 100644 --- a/README.markdown +++ b/README.markdown @@ -17,7 +17,6 @@ properly! The most requested languages are: * Scala -* Python * Javascript ... but there are many more requests to do "every language", so don't let that stop you. diff --git a/c.html.markdown b/c.html.markdown index 4ac05299..69bf099e 100644 --- a/c.html.markdown +++ b/c.html.markdown @@ -2,6 +2,7 @@ language: c author: Adam Bard author_url: http://adambard.com/ +filename: learnc.c --- Ah, C. Still the language of modern high-performance computing. @@ -12,6 +13,7 @@ memory management and C will take you as far as you need to go. ```c // Single-line comments start with // + /* Multi-line comments look like this. */ @@ -19,6 +21,7 @@ Multi-line comments look like this. // Import headers with #include #include <stdlib.h> #include <stdio.h> +#include <string.h> // Declare function signatures in advance in a .h file, or at the top of // your .c file. @@ -27,7 +30,7 @@ void function_2(); // Your program's entry point is a function called // main with an integer return type. -int main(){ +int main() { // print output using printf, for "print formatted" // %d is an integer, \n is a newline @@ -38,36 +41,49 @@ printf("%d\n", 0); // => Prints 0 // Types /////////////////////////////////////// -// Variables must always be declared with a type. +// You have to declare variables before using them. A variable declaration +// requires you to specify its type; a variable's type determines its size +// in bytes. -// 32-bit integer +// ints are usually 4 bytes int x_int = 0; -// 16-bit integer +// shorts are usually 2 bytes short x_short = 0; -// 8-bit integer, aka 1 byte +// chars are guaranteed to be 1 byte char x_char = 0; char y_char = 'y'; // Char literals are quoted with '' -long x_long = 0; // Still 32 bytes for historical reasons -long long x_long_long = 0; // Guaranteed to be at least 64 bytes +// longs are often 4 to 8 bytes; long longs are guaranteed to be at least +// 64 bits +long x_long = 0; +long long x_long_long = 0; -// 32-bit floating-point decimal +// floats are usually 32-bit floating point numbers float x_float = 0.0; -// 64-bit floating-point decimal +// doubles are usually 64-bit floating-point numbers double x_double = 0.0; -// Integer types may be unsigned +// Integral types may be unsigned. This means they can't be negative, but +// the maximum value of an unsigned variable is greater than the maximum +// value of the same size. unsigned char ux_char; unsigned short ux_short; unsigned int ux_int; unsigned long long ux_long_long; +// Other than char, which is always 1 byte, these types vary in size depending +// on your machine. sizeof(T) gives you the size of a variable with type T in +// bytes so you can express the size of these types in a portable way. +// For example, +printf("%lu\n", sizeof(int)); // => 4 (on machines with 4-byte words) + // Arrays must be initialized with a concrete size. char my_char_array[20]; // This array occupies 1 * 20 = 20 bytes int my_int_array[20]; // This array occupies 4 * 20 = 80 bytes + // (assuming 4-byte words) // You can initialize an array to 0 thusly: @@ -81,16 +97,20 @@ my_array[0]; // => 0 my_array[1] = 2; printf("%d\n", my_array[1]); // => 2 -// Strings are just lists of chars terminated by a null (0x00) byte. +// Strings are just arrays of chars terminated by a NUL (0x00) byte, +// represented in strings as the special character '\0'. +// (We don't have to include the NUL byte in string literals; the compiler +// inserts it at the end of the array for us.) char a_string[20] = "This is a string"; +printf("%s\n", a_string); // %s formats a string /* You may have noticed that a_string is only 16 chars long. -Char #17 is a null byte, 0x00 aka \0. +Char #17 is the NUL byte. Chars #18, 19 and 20 have undefined values. */ -printf("%d\n", a_string[16]); +printf("%d\n", a_string[16]); // => 0 /////////////////////////////////////// // Operators @@ -112,7 +132,8 @@ f1 / f2; // => 0.5, plus or minus epsilon // Comparison operators are probably familiar, but // there is no boolean type in c. We use ints instead. -// 0 is false, anything else is true +// 0 is false, anything else is true. (The comparison +// operators always return 0 or 1.) 3 == 2; // => 0 (false) 3 != 2; // => 1 (true) 3 > 2; // => 1 @@ -140,33 +161,33 @@ f1 / f2; // => 0.5, plus or minus epsilon // Control Structures /////////////////////////////////////// -if(0){ +if (0) { printf("I am never run\n"); -}else if(0){ +} else if (0) { printf("I am also never run\n"); -}else{ +} else { printf("I print\n"); } // While loops exist int ii = 0; -while(ii < 10){ +while (ii < 10) { printf("%d, ", ii++); // ii++ increments ii in-place, after using its value. } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " printf("\n"); int kk = 0; -do{ +do { printf("%d, ", kk); -}while(++kk < 10); // ++kk increments kk in-place, before using its value +} while (++kk < 10); // ++kk increments kk in-place, before using its value // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " printf("\n"); // For loops too int jj; -for(jj=0; jj < 10; jj++){ +for (jj=0; jj < 10; jj++) { printf("%d, ", jj); } // => prints "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, " @@ -176,8 +197,8 @@ printf("\n"); // Typecasting /////////////////////////////////////// -// Everything in C is stored somewhere in memory. You can change -// the type of a variable to choose how to read its data +// Every value in C has a type, but you can cast one value into another type +// if you want. int x_hex = 0x01; // You can assign vars with hex literals @@ -188,32 +209,53 @@ printf("%d\n", (char) x_hex); // => Prints 1 // Types will overflow without warning printf("%d\n", (char) 257); // => 1 (Max char = 255) -printf("%d\n", (short) 65537); // => 1 (Max short = 65535) + +// Integral types can be cast to floating-point types, and vice-versa. +printf("%f\n", (float)100); // %f formats a float +printf("%lf\n", (double)100); // %lf formats a double +printf("%d\n", (char)100.0); /////////////////////////////////////// // Pointers /////////////////////////////////////// -// You can retrieve the memory address of your variables, -// then mess with them. +// A pointer is a variable declared to store a memory address. Its declaration will +// also tell you the type of data it points to. You can retrieve the memory address +// of your variables, then mess with them. int x = 0; -printf("%p\n", &x); // Use & to retrive the address of a variable +printf("%p\n", &x); // Use & to retrieve the address of a variable // (%p formats a pointer) // => Prints some address in memory; +// Pointer types end with * in their declaration +int* px; // px is a pointer to an int +px = &x; // Stores the address of x in px +printf("%p\n", px); // => Prints some address in memory + +// To retreive the value at the address a pointer is pointing to, +// put * in front to de-reference it. +printf("%d\n", *px); // => Prints 0, the value of x, which is what px is pointing to the address of + +// You can also change the value the pointer is pointing to. +// We'll have to wrap the de-reference in parenthesis because +// ++ has a higher precedence than *. +(*px)++; // Increment the value px is pointing to by 1 +printf("%d\n", *px); // => Prints 1 +printf("%d\n", x); // => Prints 1 + int x_array[20]; // Arrays are a good way to allocate a contiguous block of memory int xx; -for(xx=0; xx<20; xx++){ +for (xx=0; xx<20; xx++) { x_array[xx] = 20 - xx; } // Initialize x_array to 20, 19, 18,... 2, 1 -// Pointer types end with * +// Declare a pointer of type int and initialize it to point to x_array int* x_ptr = x_array; -// This works because arrays are pointers to their first element. +// x_ptr now points to the first element in the array (the integer 20). +// This works because arrays are actually just pointers to their first element. -// Put a * in front to de-reference a pointer and retrieve the value, -// of the same type as the pointer, that the pointer is pointing at. +// Arrays are pointers to their first element printf("%d\n", *(x_ptr)); // => Prints 20 printf("%d\n", x_array[0]); // => Prints 20 @@ -221,33 +263,27 @@ printf("%d\n", x_array[0]); // => Prints 20 printf("%d\n", *(x_ptr + 1)); // => Prints 19 printf("%d\n", x_array[1]); // => Prints 19 -// Array indexes are such a thin wrapper around pointer -// arithmatic that the following works: -printf("%d\n", 0[x_array]); // => Prints 20; -printf("%d\n", 2[x_array]); // => Prints 18; - -// The above is equivalent to: -printf("%d\n", *(0 + x_ptr)); -printf("%d\n", *(2 + x_ptr)); - -// You can give a pointer a block of memory to use with malloc +// You can also dynamically allocate contiguous blocks of memory with the +// standard library function malloc, which takes one integer argument +// representing the number of bytes to allocate from the heap. int* my_ptr = (int*) malloc(sizeof(int) * 20); -for(xx=0; xx<20; xx++){ - *(my_ptr + xx) = 20 - xx; +for (xx=0; xx<20; xx++) { + *(my_ptr + xx) = 20 - xx; // my_ptr[xx] = 20-xx would also work here } // Initialize memory to 20, 19, 18, 17... 2, 1 (as ints) // Dereferencing memory that you haven't allocated gives // unpredictable results printf("%d\n", *(my_ptr + 21)); // => Prints who-knows-what? -// When you're done with a malloc'd block, you need to free it +// When you're done with a malloc'd block of memory, you need to free it, +// or else no one else can use it until your program terminates free(my_ptr); // Strings can be char arrays, but are usually represented as char // pointers: char* my_str = "This is my very own string"; -printf("%d\n", *my_str); // 84 (The ascii value of 'T') +printf("%c\n", *my_str); // => 'T' function_1(); } // end main function @@ -260,12 +296,12 @@ function_1(); // <return type> <function name>(<args>) int add_two_ints(int x1, int x2){ - return x1 + x2; // Use return a return a value + return x1 + x2; // Use return to return a value } /* -Pointers are passed-by-reference (duh), so functions -can mutate their values. +Functions are pass-by-value, but you can make your own references +with pointers so functions can mutate their values. Example: in-place string reversal */ @@ -333,4 +369,6 @@ int area(rect r){ Best to find yourself a copy of [K&R, aka "The C Programming Language"](https://en.wikipedia.org/wiki/The_C_Programming_Language) +Another good resource is [Learn C the hard way](http://c.learncodethehardway.org/book/) + Other than that, Google is your friend. diff --git a/clojure.html.markdown b/clojure.html.markdown index 5086d2c2..39a27bcf 100644 --- a/clojure.html.markdown +++ b/clojure.html.markdown @@ -2,9 +2,10 @@ language: clojure author: Adam Bard author_url: http://adambard.com/ +filename: learnclojure.clj --- -Clojure is a variant of LISP developed for the Java Virtual Machine. It has +Clojure is a Lisp family language developed for the Java Virtual Machine. It has a much stronger emphasis on pure [functional programming](https://en.wikipedia.org/wiki/Functional_programming) than Common Lisp, but includes several [STM](https://en.wikipedia.org/wiki/Software_transactional_memory) utilities to handle state as it comes up. @@ -12,6 +13,9 @@ state as it comes up. This combination allows it to handle concurrent processing very simply, and often automatically. +(You need a version of Clojure 1.2 or newer) + + ```clojure ; Comments start with semicolons. @@ -20,9 +24,9 @@ and often automatically. ; ; The clojure reader assumes that the first thing is a ; function or macro to call, and the rest are arguments. -; -; Here's a function that sets the current namespace: -(ns test) + +; The first call in a file should be ns, to set the namespace +(ns learnclojure) ; More basic examples: @@ -56,15 +60,18 @@ and often automatically. (class false) ; Booleans are java.lang.Boolean (class nil); The "null" value is called nil -; If you want to create a literal list of data, use ' to make a "symbol" +; If you want to create a literal list of data, use ' to stop it from +; being evaluated '(+ 1 2) ; => (+ 1 2) +; (shorthand for (quote (+ 1 2)) -; You can eval symbols. +; You can eval a quoted list (eval '(+ 1 2)) ; => 3 ; Collections & Sequences ;;;;;;;;;;;;;;;;;;; +; Lists are linked-list data structures, while Vectors are array-backed. ; Vectors and Lists are java classes too! (class [1 2 3]); => clojure.lang.PersistentVector (class '(1 2 3)); => clojure.lang.PersistentList @@ -73,16 +80,18 @@ and often automatically. ; it to stop the reader thinking it's a function. ; Also, (list 1 2 3) is the same as '(1 2 3) +; "Collections" are just groups of data ; Both lists and vectors are collections: (coll? '(1 2 3)) ; => true (coll? [1 2 3]) ; => true +; "Sequences" (seqs) are abstract descriptions of lists of data. ; Only lists are seqs. (seq? '(1 2 3)) ; => true (seq? [1 2 3]) ; => false -; Seqs are an interface for logical lists, which can be lazy. -; "Lazy" means that a seq can define an infinite series, like so: +; A seq need only provide an entry when it is accessed. +; So, seqs which can be lazy -- they can define infinite series: (range 4) ; => (0 1 2 3) (range) ; => (0 1 2 3 4 ...) (an infinite series) (take 4 (range)) ; (0 1 2 3) @@ -91,8 +100,8 @@ and often automatically. (cons 4 [1 2 3]) ; => (4 1 2 3) (cons 4 '(1 2 3)) ; => (4 1 2 3) -; Use conj to add an item to the beginning of a list, -; or the end of a vector +; Conj will add an item to a collection in the most efficient way. +; For lists, they insert at the beginning. For vectors, they insert at the end. (conj [1 2 3] 4) ; => [1 2 3 4] (conj '(1 2 3) 4) ; => (4 1 2 3) @@ -162,20 +171,26 @@ x ; => 1 ; => "Hello Finn, you passed 3 extra args" -; Hashmaps +; Maps ;;;;;;;;;; +; Hash maps and array maps share an interface. Hash maps have faster lookups +; but don't retain key order. (class {:a 1 :b 2 :c 3}) ; => clojure.lang.PersistentArrayMap +(class (hash-map :a 1 :b 2 :c 3)) ; => clojure.lang.PersistentHashMap + +; Arraymaps will automatically become hashmaps through most operations +; if they get big enough, so you don't need to worry. +; Maps can use any hashable type as a key, but usually keywords are best ; Keywords are like strings with some efficiency bonuses (class :a) ; => clojure.lang.Keyword -; Maps can use any type as a key, but usually keywords are best -(def stringmap (hash-map "a" 1, "b" 2, "c" 3)) +(def stringmap {"a" 1, "b" 2, "c" 3}) stringmap ; => {"a" 1, "b" 2, "c" 3} -(def keymap (hash-map :a 1 :b 2 :c 3)) -keymap ; => {:a 1, :c 3, :b 2} (order is not guaranteed) +(def keymap {:a 1, :b 2, :c 3}) +keymap ; => {:a 1, :c 3, :b 2} ; By the way, commas are always treated as whitespace and do nothing. @@ -194,7 +209,8 @@ keymap ; => {:a 1, :c 3, :b 2} (order is not guaranteed) (stringmap "d") ; => nil ; Use assoc to add new keys to hash-maps -(assoc keymap :d 4) ; => {:a 1, :b 2, :c 3, :d 4} +(def newkeymap (assoc keymap :d 4)) +newkeymap ; => {:a 1, :b 2, :c 3, :d 4} ; But remember, clojure types are immutable! keymap ; => {:a 1, :b 2, :c 3} @@ -265,6 +281,7 @@ keymap ; => {:a 1, :b 2, :c 3} (require 'clojure.string) ; Use / to call functions from a module +; Here, the module is clojure.string and the function is blank? (clojure.string/blank? "") ; => true ; You can give a module a shorter name on import @@ -308,4 +325,56 @@ keymap ; => {:a 1, :b 2, :c 3} (doto (Calendar/getInstance) (.set 2000 1 1 0 0 0) .getTime) ; => A Date. set to 2000-01-01 00:00:00 + +; STM +;;;;;;;;;;;;;;;;; + +; Software Transactional Memory is the mechanism clojure uses to handle +; persistent state. There are a few constructs in clojure that use this. + +; An atom is the simplest. Pass it an initial value +(def my-atom (atom {})) + +; Update an atom with swap!. +; swap! takes a function and calls it with the current value of the atom +; as the first argument, and any trailing arguments as the second +(swap! my-atom assoc :a 1) ; Sets my-atom to the result of (assoc {} :a 1) +(swap! my-atom assoc :b 2) ; Sets my-atom to the result of (assoc {:a 1} :b 2) + + ; Use '@' to dereference the atom and get the value +my-atom ;=> Atom<#...> (Returns the Atom object) +@my-atom ; => {:a 1 :b 2} + +; Here's a simple counter using an atom +(def counter (atom 0)) +(defn inc-counter [] + (swap! counter inc)) + +(inc-counter) +(inc-counter) +(inc-counter) +(inc-counter) +(inc-counter) + +@counter ; => 5 + +; Other STM constructs are refs and agents. +; Refs: http://clojure.org/refs +; Agents: http://clojure.org/agents ``` + +### Further Reading + +This is far from exhaustive, but hopefully it's enought o get you on your feet. + +Clojure.org has lots of articles: +[http://clojure.org/](http://clojure.org/) + +Clojuredocs.org has documentation with examples for most core functions: +[http://clojuredocs.org/quickref/Clojure%20Core](http://clojuredocs.org/quickref/Clojure%20Core) + +4Clojure is a great way to build your clojure/FP skills: +[http://www.4clojure.com/](http://www.4clojure.com/) + +Clojure-doc.org (yeah, really) has a number of getting started articles: +[http://clojure-doc.org/](http://clojure-doc.org/) diff --git a/dart.html.markdown b/dart.html.markdown new file mode 100644 index 00000000..27365746 --- /dev/null +++ b/dart.html.markdown @@ -0,0 +1,507 @@ +--- +language: dart +author: Joao Pedrosa +author_url: https://github.com/jpedrosa/ +filename: learndart.dart +--- + +Dart is a newcomer into the realm of programming languages. +It borrows a lot from other mainstream languages, having as a goal not to deviate too much from +its JavaScript sibling. Like JavaScript, Dart aims for great browser integration. + +Dart's most controversial feature must be its Optional Typing. + +```javascript +import "dart:collection"; +import "dart:math" as DM; + +// Welcome to Learn Dart in 15 minutes. http://www.dartlang.org/ +// This is an executable tutorial. You can run it with Dart or on +// the Try Dart! site if you copy/paste it there. http://try.dartlang.org/ + +// Function declaration and method declaration look the same. Function +// declarations can be nested. The declaration takes the form of +// name() {} or name() => singleLineExpression; +// The fat arrow function declaration has an implicit return for the result of +// the expression. +example1() { + example1nested1() { + example1nested2() => print("Example1 nested 1 nested 2"); + example1nested2(); + } + example1nested1(); +} + +// Anonymous functions don't include a name. +example2() { + example2nested1(fn) { + fn(); + } + example2nested1(() => print("Example2 nested 1")); +} + +// When a function parameter is declared, the declaration can include the +// number of parameters the function takes by specifying the names of the +// parameters it takes. +example3() { + example3nested1(fn(informSomething)) { + fn("Example3 nested 1"); + } + example3planB(fn) { // Or don't declare number of parameters. + fn("Example3 plan B"); + } + example3nested1((s) => print(s)); + example3planB((s) => print(s)); +} + +// Functions have closure access to outer variables. +var example4Something = "Example4 nested 1"; +example4() { + example4nested1(fn(informSomething)) { + fn(example4Something); + } + example4nested1((s) => print(s)); +} + +// Class declaration with a sayIt method, which also has closure access +// to the outer variable as though it were a function as seen before. +var example5method = "Example5 sayIt"; +class Example5Class { + sayIt() { + print(example5method); + } +} +example5() { + // Create an anonymous instance of the Example5Class and call the sayIt + // method on it. + new Example5Class().sayIt(); +} + +// Class declaration takes the form of class name { [classBody] }. +// Where classBody can include instance methods and variables, but also +// class methods and variables. +class Example6Class { + var example6InstanceVariable = "Example6 instance variable"; + sayIt() { + print(example6InstanceVariable); + } +} +example6() { + new Example6Class().sayIt(); +} + +// Class methods and variables are declared with "static" terms. +class Example7Class { + static var example7ClassVariable = "Example7 class variable"; + static sayItFromClass() { + print(example7ClassVariable); + } + sayItFromInstance() { + print(example7ClassVariable); + } +} +example7() { + Example7Class.sayItFromClass(); + new Example7Class().sayItFromInstance(); +} + +// Literals are great, but there's a restriction for what literals can be +// outside of function/method bodies. Literals on the outer scope of class +// or outside of class have to be constant. Strings and numbers are constant +// by default. But arrays and maps are not. They can be made constant by +// declaring them "const". +var example8A = const ["Example8 const array"], + example8M = const {"someKey": "Example8 const map"}; +example8() { + print(example8A[0]); + print(example8M["someKey"]); +} + +// Loops in Dart take the form of standard for () {} or while () {} loops, +// slightly more modern for (.. in ..) {}, or functional callbacks with many +// supported features, starting with forEach. +var example9A = const ["a", "b"]; +example9() { + for (var i = 0; i < example9A.length; i++) { + print("Example9 for loop '${example9A[i]}'"); + } + var i = 0; + while (i < example9A.length) { + print("Example9 while loop '${example9A[i]}'"); + i++; + } + for (var e in example9A) { + print("Example9 for-in loop '${e}'"); + } + example9A.forEach((e) => print("Example9 forEach loop '${e}'")); +} + +// To loop over the characters of a string or to extract a substring. +var example10S = "ab"; +example10() { + for (var i = 0; i < example10S.length; i++) { + print("Example10 String character loop '${example10S[i]}'"); + } + for (var i = 0; i < example10S.length; i++) { + print("Example10 substring loop '${example10S.substring(i, i + 1)}'"); + } +} + +// Int and double are the two supported number formats. +example11() { + var i = 1 + 320, d = 3.2 + 0.01; + print("Example11 int ${i}"); + print("Example11 double ${d}"); +} + +// DateTime provides date/time arithmetic. +example12() { + var now = new DateTime.now(); + print("Example12 now '${now}'"); + now = now.add(new Duration(days: 1)); + print("Example12 tomorrow '${now}'"); +} + +// Regular expressions are supported. +example13() { + var s1 = "some string", s2 = "some", re = new RegExp("^s.+?g\$"); + match(s) { + if (re.hasMatch(s)) { + print("Example13 regexp matches '${s}'"); + } else { + print("Example13 regexp doesn't match '${s}'"); + } + } + match(s1); + match(s2); +} + +// Boolean expressions need to resolve to either true or false, as no +// implicit conversions are supported. +example14() { + var v = true; + if (v) { + print("Example14 value is true"); + } + v = null; + try { + if (v) { + // Never runs + } else { + // Never runs + } + } catch (e) { + print("Example14 null value causes an exception: '${e}'"); + } +} + +// try/catch/finally and throw are used for exception handling. +// throw takes any object as parameter; +example15() { + try { + try { + throw "Some unexpected error."; + } catch (e) { + print("Example15 an exception: '${e}'"); + throw e; // Re-throw + } + } catch (e) { + print("Example15 catch exception being re-thrown: '${e}'"); + } finally { + print("Example15 Still run finally"); + } +} + +// To be efficient when creating a long string dynamically, use +// StringBuffer. Or you could join a string array. +example16() { + var sb = new StringBuffer(), a = ["a", "b", "c", "d"], e; + for (e in a) { sb.write(e); } + print("Example16 dynamic string created with " + "StringBuffer '${sb.toString()}'"); + print("Example16 join string array '${a.join()}'"); +} + +// Strings can be concatenated by just having string literals next to +// one another with no further operator needed. +example17() { + print("Example17 " + "concatenate " + "strings " + "just like that"); +} + +// Strings have single-quote or double-quote for delimiters with no +// actual difference between the two. The given flexibility can be good +// to avoid the need to escape content that matches the delimiter being +// used. For example, double-quotes of HTML attributes if the string +// contains HTML content. +example18() { + print('Example18 <a href="etc">' + "Don't can't I'm Etc" + '</a>'); +} + +// Strings with triple single-quotes or triple double-quotes span +// multiple lines and include line delimiters. +example19() { + print('''Example19 <a href="etc"> +Example19 Don't can't I'm Etc +Example19 </a>'''); +} + +// Strings have the nice interpolation feature with the $ character. +// With $ { [expression] }, the return of the expression is interpolated. +// $ followed by a variable name interpolates the content of that variable. +// $ can be escaped like so \$ to just add it to the string instead. +example20() { + var s1 = "'\${s}'", s2 = "'\$s'"; + print("Example20 \$ interpolation ${s1} or $s2 works."); +} + +// Optional types allow for the annotation of APIs and come to the aid of +// IDEs so the IDEs can better refactor, auto-complete and check for +// errors. So far we haven't declared any types and the programs have +// worked just fine. In fact, types are disregarded during runtime. +// Types can even be wrong and the program will still be given the +// benefit of the doubt and be run as though the types didn't matter. +// There's a runtime parameter that checks for type errors which is +// the checked mode, which is said to be useful during development time, +// but which is also slower because of the extra checking and is thus +// avoided during deployment runtime. +class Example21 { + List<String> _names; + Example21() { + _names = ["a", "b"]; + } + List<String> get names => _names; + set names(List<String> list) { + _names = list; + } + int get length => _names.length; + void add(String name) { + _names.add(name); + } +} +void example21() { + Example21 o = new Example21(); + o.add("c"); + print("Example21 names '${o.names}' and length '${o.length}'"); + o.names = ["d", "e"]; + print("Example21 names '${o.names}' and length '${o.length}'"); +} + +// Class inheritance takes the form of class name extends AnotherClassName {}. +class Example22A { + var _name = "Some Name!"; + get name => _name; +} +class Example22B extends Example22A {} +example22() { + var o = new Example22B(); + print("Example22 class inheritance '${o.name}'"); +} + +// Class mixin is also available, and takes the form of +// class name extends SomeClass with AnotherClassName {}. +// It's necessary to extend some class to be able to mixin another one. +// The template class of mixin cannot at the moment have a constructor. +// Mixin is mostly used to share methods with distant classes, so the +// single inheritance doesn't get in the way of reusable code. +// Mixins follow the "with" statement during the class declaration. +class Example23A {} +class Example23Utils { + addTwo(n1, n2) { + return n1 + n2; + } +} +class Example23B extends Example23A with Example23Utils { + addThree(n1, n2, n3) { + return addTwo(n1, n2) + n3; + } +} +example23() { + var o = new Example23B(), r1 = o.addThree(1, 2, 3), + r2 = o.addTwo(1, 2); + print("Example23 addThree(1, 2, 3) results in '${r1}'"); + print("Example23 addTwo(1, 2) results in '${r2}'"); +} + +// The Class constructor method uses the same name of the class and +// takes the form of SomeClass() : super() {}, where the ": super()" +// part is optional and it's used to delegate constant parameters to the +// super-parent's constructor. +class Example24A { + var _value; + Example24A({value: "someValue"}) { + _value = value; + } + get value => _value; +} +class Example24B extends Example24A { + Example24B({value: "someOtherValue"}) : super(value: value); +} +example24() { + var o1 = new Example24B(), + o2 = new Example24B(value: "evenMore"); + print("Example24 calling super during constructor '${o1.value}'"); + print("Example24 calling super during constructor '${o2.value}'"); +} + +// There's a shortcut to set constructor parameters in case of simpler classes. +// Just use the this.parameterName prefix and it will set the parameter on +// an instance variable of same name. +class Example25 { + var value, anotherValue; + Example25({this.value, this.anotherValue}); +} +example25() { + var o = new Example25(value: "a", anotherValue: "b"); + print("Example25 shortcut for constructor '${o.value}' and " + "'${o.anotherValue}'"); +} + +// Named parameters are available when declared between {}. +// Parameter order can be optional when declared between {}. +// Parameters can be made optional when declared between []. +example26() { + var _name, _surname, _email; + setConfig1({name, surname}) { + _name = name; + _surname = surname; + } + setConfig2(name, [surname, email]) { + _name = name; + _surname = surname; + _email = email; + } + setConfig1(surname: "Doe", name: "John"); + print("Example26 name '${_name}', surname '${_surname}', " + "email '${_email}'"); + setConfig2("Mary", "Jane"); + print("Example26 name '${_name}', surname '${_surname}', " + "email '${_email}'"); +} + +// Variables declared with final can only be set once. +// In case of classes, final instance variables can be set via constant +// constructor parameter. +class Example27 { + final color1, color2; + // A little flexibility to set final instance variables with syntax + // that follows the : + Example27({this.color1, color2}) : color2 = color2; +} +example27() { + final color = "orange", o = new Example27(color1: "lilac", color2: "white"); + print("Example27 color is '${color}'"); + print("Example27 color is '${o.color1}' and '${o.color2}'"); +} + +// To import a library, use import "libraryPath" or if it's a core library, +// import "dart:libraryName". There's also the "pub" package management with +// its own convention of import "package:packageName". +// See import "dart:collection"; at the top. Imports must come before +// other code declarations. IterableBase comes from dart:collection. +class Example28 extends IterableBase { + var names; + Example28() { + names = ["a", "b"]; + } + get iterator => names.iterator; +} +example28() { + var o = new Example28(); + o.forEach((name) => print("Example28 '${name}'")); +} + +// For control flow we have: +// * standard switch with must break statements +// * if-else if-else and ternary ..?..:.. operator +// * closures and anonymous functions +// * break, continue and return statements +example29() { + var v = true ? 30 : 60; + switch (v) { + case 30: + print("Example29 switch statement"); + break; + } + if (v < 30) { + } else if (v > 30) { + } else { + print("Example29 if-else statement"); + } + callItForMe(fn()) { + return fn(); + } + rand() { + v = new DM.Random().nextInt(50); + return v; + } + while (true) { + print("Example29 callItForMe(rand) '${callItForMe(rand)}'"); + if (v != 30) { + break; + } else { + continue; + } + // Never gets here. + } +} + +// Parse int, convert double to int, or just keep int when dividing numbers +// by using the ~/ operation. Let's play a guess game too. +example30() { + var gn, tooHigh = false, + n, n2 = (2.0).toInt(), top = int.parse("123") ~/ n2, bottom = 0; + top = top ~/ 6; + gn = new DM.Random().nextInt(top + 1); // +1 because nextInt top is exclusive + print("Example30 Guess a number between 0 and ${top}"); + guessNumber(i) { + if (n == gn) { + print("Example30 Guessed right! The number is ${gn}"); + } else { + tooHigh = n > gn; + print("Example30 Number ${n} is too " + "${tooHigh ? 'high' : 'low'}. Try again"); + } + return n == gn; + } + n = (top - bottom) ~/ 2; + while (!guessNumber(n)) { + if (tooHigh) { + top = n - 1; + } else { + bottom = n + 1; + } + n = bottom + ((top - bottom) ~/ 2); + } +} + +// Programs have only one entry point in the main function. +// Nothing is expected to be executed on the outer scope before a program +// starts running with what's in its main function. +// This helps with faster loading and even lazily loading of just what +// the program needs to startup with. +main() { + print("Learn Dart in 15 minutes!"); + [example1, example2, example3, example4, example5, example6, example7, + example8, example9, example10, example11, example12, example13, example14, + example15, example16, example17, example18, example19, example20, + example21, example22, example23, example24, example25, example26, + example27, example28, example29, example30 + ].forEach((ef) => ef()); +} + +``` + +## Further Reading + +Dart has a comprehenshive web-site. It covers API reference, tutorials, articles and more, including a +useful Try Dart online. +http://www.dartlang.org/ +http://try.dartlang.org/ + + + diff --git a/elixir.html.markdown b/elixir.html.markdown new file mode 100644 index 00000000..2e9aa5a1 --- /dev/null +++ b/elixir.html.markdown @@ -0,0 +1,398 @@ +--- +language: elixir +author: Joao Marques +author_url: http://github.com/mrshankly +filename: learnelixir.ex +--- + +Elixir is a modern functional language built on top of the Erlang VM. +It's fully compatible with Erlang, but features a more standard syntax +and many more features. + +```ruby + +# Single line comments start with a hashtag. + +# There's no multi-line comment, +# but you can stack multiple comments. + +# To use the elixir shell use the `iex` command. +# Compile your modules with the `elixirc` command. + +# Both should be in your path if you installed elixir correctly. + +## --------------------------- +## -- Basic types +## --------------------------- + +# There are numbers +3 # integer +0x1F # integer +3.0 # float + +# Atoms, that are literals, a constant with name. They start with `:`. +:hello # atom + +# Tuples that are stored contigously in memory. +{1,2,3} # tuple + +# We can access a tuple element with the `elem` function: +elem({1, 2, 3}, 0) #=> 1 + +# Lists that are implemented as linked lists. +[1,2,3] # list + +# We can access the head and tail of a list as follows: +[head | tail] = [1,2,3] +head #=> 1 +tail #=> [2,3] + +# In elixir, just like in erlang, the `=` denotes pattern matching and +# not an assignment. +# +# This means that the left-hand side (pattern) is matched against a +# right-hand side. +# +# This is how the above example of accessing the head and tail of a list works. + +# A pattern match will error when the sides don't match, in this example +# the tuples have different sizes. +# {a, b, c} = {1, 2} #=> ** (MatchError) no match of right hand side value: {1,2} + +# There's also binaries +<<1,2,3>> # binary + +# Strings and char lists +"hello" # string +'hello' # char list + +# Multi-line strings +""" +I'm a multi-line +string. +""" +#=> "I'm a multi-line\nstring.\n" + +# Strings are all encoded in UTF-8: +"héllò" #=> "héllò" + +# Strings are really just binaries, and char lists are just lists. +<<?a, ?b, ?c>> #=> "abc" +[?a, ?b, ?c] #=> 'abc' + +# `?a` in elixir returns the ASCII integer for the letter `a` +?a #=> 97 + +# To concatenate lists use `++`, for binaries use `<>` +[1,2,3] ++ [4,5] #=> [1,2,3,4,5] +'hello ' ++ 'world' #=> 'hello world' + +<<1,2,3>> <> <<4,5>> #=> <<1,2,3,4,5>> +"hello " <> "world" #=> "hello world" + +## --------------------------- +## -- Operators +## --------------------------- + +# Some math +1 + 1 #=> 2 +10 - 5 #=> 5 +5 * 2 #=> 10 +10 / 2 #=> 5.0 + +# In elixir the operator `/` always returns a float. + +# To do integer division use `div` +div(10, 2) #=> 5 + +# To get the division remainder use `rem` +rem(10, 3) #=> 1 + +# There's also boolean operators: `or`, `and` and `not`. +# These operators expect a boolean as their first argument. +true and true #=> true +false or true #=> true +# 1 and true #=> ** (ArgumentError) argument error + +# Elixir also provides `||`, `&&` and `!` which accept arguments of any type. +# All values except `false` and `nil` will evaluate to true. +1 || true #=> 1 +false && 1 #=> false +nil && 20 #=> nil + +!true #=> false + +# For comparisons we have: `==`, `!=`, `===`, `!==`, `<=`, `>=`, `<` and `>` +1 == 1 #=> true +1 != 1 #=> false +1 < 2 #=> true + +# `===` and `!==` are more strict when comparing integers and floats: +1 == 1.0 #=> true +1 === 1.0 #=> false + +# We can also compare two different data types: +1 < :hello #=> true + +# The overall sorting order is defined below: +# number < atom < reference < functions < port < pid < tuple < list < bit string + +# To quote Joe Armstrong on this: "The actual order is not important, +# but that a total ordering is well defined is important." + +## --------------------------- +## -- Control Flow +## --------------------------- + +# `if` expression +if false do + "This will never be seen" +else + "This will" +end + +# There's also `unless` +unless true do + "This will never be seen" +else + "This will" +end + +# Remember pattern matching? Many control-flow structures in elixir rely on it. + +# `case` allows us to compare a value against many patterns: +case {:one, :two} do + {:four, :five} -> + "This won't match" + {:one, x} -> + "This will match and assign `x` to `:two`" + _ -> + "This will match any value" +end + +# It's common practive to assign a value to `_` if we don't need it. +# For example, if only the head of a list matters to us: +[head | _] = [1,2,3] +head #=> 1 + +# For better readability we can do the following: +[head | _tail] = [:a, :b, :c] +head #=> :a + +# `cond` lets us check for many conditions at the same time. +# Use `cond` instead of nesting many `if` expressions. +cond do + 1 + 1 == 3 -> + "I will never be seen" + 2 * 5 == 12 -> + "Me neither" + 1 + 2 == 3 -> + "But I will" +end + +# It is common to see a last condition equal to `true`, which will always match. +cond do + 1 + 1 == 3 -> + "I will never be seen" + 2 * 5 == 12 -> + "Me neither" + true -> + "But I will (this is essentially an else)" +end + +# `try/catch` is used to catch values that are thrown, it also supports an +# `after` clause that is invoked whether or not a value is catched. +try do + throw(:hello) +catch + message -> "Got #{message}." +after + IO.puts("I'm the after clause.") +end +#=> I'm the after clause +# "Got :hello" + +## --------------------------- +## -- Modules and Functions +## --------------------------- + +# Anonymous functions (notice the dot) +square = fn(x) -> x * x end +square.(5) #=> 25 + +# They also accept many clauses and guards. +# Guards let you fine tune pattern matching, +# they are indicated by the `when` keyword: +f = fn + x, y when x > 0 -> x + y + x, y -> x * y +end + +f.(1, 3) #=> 4 +f.(-1, 3) #=> -3 + +# Elixir also provides many built-in functions. +# These are available in the current scope. +is_number(10) #=> true +is_list("hello") #=> false +elem({1,2,3}, 0) #=> 1 + +# You can group several functions into a module. Inside a module use `def` +# to define your functions. +defmodule Math do + def sum(a, b) do + a + b + end + + def square(x) do + x * x + end +end + +Math.sum(1, 2) #=> 3 +Math.square(3) #=> 9 + +# To compile our simple Math module save it as `math.ex` and use `elixirc` +# in your terminal: elixirc math.ex + +# Inside a module we can define functions with `def` and private functions with `defp`. +# A function defined with `def` is available to be invoked from other modules, +# a private function can only be invoked locally. +defmodule PrivateMath do + def sum(a, b) do + do_sum(a, b) + end + + defp do_sum(a, b) do + a + b + end +end + +PrivateMath.sum(1, 2) #=> 3 +# PrivateMath.do_sum(1, 2) #=> ** (UndefinedFunctionError) + +# Function declarations also support guards and multiple clauses: +defmodule Geometry do + def area({:rectangle, w, h}) do + w * h + end + + def area({:circle, r}) when is_number(r) do + 3.14 * r * r + end +end + +Geometry.area({:rectangle, 2, 3}) #=> 6 +Geometry.area({:circle, 3}) #=> 28.25999999999999801048 +# Geometry.area({:circle, "not_a_number"}) +#=> ** (FunctionClauseError) no function clause matching in Geometry.area/1 + +# Due to immutability, recursion is a big part of elixir +defmodule Recursion do + def sum_list([head | tail], acc) do + sum_list(tail, acc + head) + end + + def sum_list([], acc) do + acc + end +end + +Recursion.sum_list([1,2,3], 0) #=> 6 + +# Elixir modules support attributes, there are built-in attributes and you +# may also add custom attributes. +defmodule MyMod do + @moduledoc """ + This is a built-in attribute on a example module. + """ + + @my_data 100 # This is a custom attribute. + IO.inspect(@my_data) #=> 100 +end + +## --------------------------- +## -- Records and Exceptions +## --------------------------- + +# Records are basically structures that allow you to associate a name with +# a particular value. +defrecord Person, name: nil, age: 0, height: 0 + +joe_info = Person.new(name: "Joe", age: 30, height: 180) +#=> Person[name: "Joe", age: 30, height: 180] + +# Access the value of name +joe_info.name #=> "Joe" + +# Update the value of age +joe_info = joe_info.age(31) #=> Person[name: "Joe", age: 31, height: 180] + +# The `try` block with the `rescue` keyword is used to handle exceptions +try do + raise "some error" +rescue + RuntimeError -> "rescued a runtime error" + _error -> "this will rescue any error" +end + +# All exceptions have a message +try do + raise "some error" +rescue + x in [RuntimeError] -> + x.message +end + +## --------------------------- +## -- Concurrency +## --------------------------- + +# Elixir relies on the actor model for concurrency. All we need to write +# concurrent programs in elixir are three primitives: spawning processes, +# sending messages and receiving messages. + +# To start a new process we use the `spawn` function, which takes a function +# as argument. +f = fn -> 2 * 2 end #=> #Function<erl_eval.20.80484245> +spawn(f) #=> #PID<0.40.0> + +# `spawn` returns a pid (process identifier), you can use this pid to send +# messages to the process. To do message passing we use the `<-` operator. +# For all of this to be useful we need to be able to receive messages. This is +# achived with the `receive` mechanism: +defmodule Geometry do + def area_loop do + receive do + {:rectangle, w, h} -> + IO.puts("Area = #{w * h}") + area_loop() + {:circle, r} -> + IO.puts("Area = #{3.14 * r * r}") + area_loop() + end + end +end + +# Compile the module and create a process that evaluates `area_loop` in the shell +pid = spawn(fn -> Geometry.area_loop() end) #=> #PID<0.40.0> + +# Send a message to `pid` that will match a pattern in the receive statement +pid <- {:rectangle, 2, 3} +#=> Area = 6 +# {:rectangle,2,3} + +pid <- {:circle, 2} +#=> Area = 12.56000000000000049738 +# {:circle,2} + +# The shell is also a process, you can use `self` to get the current pid +self() #=> #PID<0.27.0> +``` + +## References + +* [Getting started guide](http://elixir-lang.org/getting_started/1.html) from [elixir webpage](http://elixir-lang.org) +* [Elixir Documentation](http://elixir-lang.org/docs/master/) +* ["Learn You Some Erlang for Great Good!"](http://learnyousomeerlang.com/) by Fred Hebert +* "Programming Erlang: Software for a Concurrent World" by Joe Armstrong diff --git a/erlang.html.markdown b/erlang.html.markdown new file mode 100644 index 00000000..42d0b809 --- /dev/null +++ b/erlang.html.markdown @@ -0,0 +1,239 @@ +--- +language: erlang +author: Giovanni Cappellotto +author_url: http://www.focustheweb.com/ +filename: learnerlang.erl +--- + +```erlang +% Percent sign start a one-line comment. + +%% Two percent characters shall be used to comment functions. + +%%% Three percent characters shall be used to comment modules. + +% We use three types of punctuation in Erlang. +% Commas (`,`) separate arguments in function calls, data constructors, and +% patterns. +% Periods (`.`) (followed by whitespace) separate entire functions and +% expressions in the shell. +% Semicolons (`;`) separate clauses. We find clauses in several contexts: in kn +% function definitions and in `case`, `if`, `try..catch` and `receive` +% expressions. + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%% 1. Variables and pattern matching. +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +Num = 42. % All variable names must start with an uppercase letter. +% Erlang has single assignment variables, if you try to assign a different value +% to the variable `Num`, you’ll get an error. + +% In most languages, `=` denotes an assignment statement. In Erlang, however, +% `=` denotes a pattern matching operation. `Lhs = Rhs` really means this: +% evaluate the right side (Rhs), and then match the result against the pattern +% on the left side (Lhs). +Num = 7 * 6. + +% Floating point number. +Pi = 3.14159. + +% Atoms, are used to represent different non-numerical constant values. Atoms +% start with lowercase letters, followed by a sequence of alphanumeric +% characters or the underscore (`_`) or at (`@`) sign. +Hello = hello. + +% Tuples are similar to structs in C. +Point = {point, 10, 45}. + +% If we want to extract some values from a tuple, we use the pattern matching +% operator `=`. +{point, X, Y} = Point. % X = 10, Y = 45 + +% We can use `_` as a placeholder for variables that we’re not interested in. +% The symbol `_` is called an anonymous variable. Unlike regular variables, +% several occurrences of _ in the same pattern don’t have to bind to the same +% value. +Person = {person, {name, {first, joe}, {last, armstrong}}, {footsize, 42}}. +{_, {_, {_, Who}, _}, _} = Person. % Who = joe + +% We create a list by enclosing the list elements in square brackets and +% separating them with commas. +% The individual elements of a list can be of any type. +% The first element of a list the head of the list. If you imagine removing the +% head from the list, what’s left is called the tail of the list. +ThingsToBuy = [{apples, 10}, {pears, 6}, {milk, 3}]. + +% If `T` is a list, then `[H|T]` is also a list, with head H and tail T. +% The vertical bar (`|`) separates the head of a list from its tail. +% `[]` is the empty list. +% We can extract elements from a list with a pattern matching operation. If we +% have the nonempty list `L`, then the expression `[X|Y] = L`, where `X` and `Y` +% are unbound variables, will extract the head of the list into `X` and the tail +% of the list into `Y`. +[FirstThing|OtherThingsToBuy] = ThingsToBuy. +% FirstThing = {apples, 10} +% OtherThingsToBuy = {pears, 6}, {milk, 3} + +% There are no strings in Erlang. Strings are really just lists of integers. +% Strings are enclosed in double quotation marks (`"`). +Name = "Hello". + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%% 2. Sequential programming. +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +% Modules are the basic unit of code in Erlang. All the functions we write are +% stored in modules. Modules are stored in files with `.erl` extensions. +% Modules must be compiled before the code can be run. A compiled module has the +% extension `.beam`. +-module(geometry). +-export([area/1]). + +% The function area consists of two clauses. The clauses are separated by a +% semicolon, and the final clause is terminated by dot-whitespace. +% Each clause has a head and a body; the head consists of a function name +% followed by a pattern (in parentheses), and the body consists of a sequence of +% expressions, which are evaluated if the pattern in the head is successfully +% matched against the calling arguments. The patterns are matched in the order +% they appear in the function definition. +area({rectangle, Width, Ht}) -> Width * Ht; +area({circle, R}) -> 3.14159 * R * R. + +% Compile the code in the file geometry.erl. +c(geometry). % {ok,geometry} + +% We need to include the module name together with the function name in order to +% identify exactly which function we want to call. +geometry:area({rectangle, 10, 5}). % 50 +geometry:area({circle, 1.4}). % 6.15752 + +% In Erlang, two functions with the same name and different arity in the same +% module represent entirely different functions. +-module(lib_misc). +-export([sum/1]). +sum(L) -> sum(L, 0). +sum([], N) -> N; +sum([H|T], N) -> sum(T, H+N). + +% Funs are "anonymous" functions. They are called this because they have no +% name. +Double = fun(X) -> 2*X end. +Double(2). % 4 + +% Functions accept funs as their arguments and can return funs. +Mult = fun(Times) -> ( fun(X) -> X * Times end ) end. +Triple = Mult(3). +Triple(5). % 15 + +% List comprehensions are expressions that create lists without having to use +% funs, maps, or filters. +% The notation `[F(X) || X <- L]` means "the list of `F(X)` where `X` is taken +% from the list `L`." +L = [1,2,3,4,5]. +[2*X || X <- L]. % [2,4,6,8,10] + +% Guards are constructs that we can use to increase the power of pattern +% matching. Using guards, we can perform simple tests and comparisons on the +% variables in a pattern. +% You can use guards in the heads of function definitions where they are +% introduced by the `when` keyword, or you can use them at any place in the +% language where an expression is allowed. +max(X, Y) when X > Y -> X; +max(X, Y) -> Y. + +% A guard is a series of guard expressions, separated by commas (`,`). +% The guard `GuardExpr1, GuardExpr2, ..., GuardExprN` is true if all the guard +% expressions `GuardExpr1, GuardExpr2, ...` evaluate to true. +is_cat(A) when is_atom(A), A =:= cat -> true; +is_cat(A) -> false. +is_dog(A) when is_atom(A), A =:= dog -> true; +is_dog(A) -> false. + +% A `guard sequence` is either a single guard or a series of guards, separated +%by semicolons (`;`). The guard sequence `G1; G2; ...; Gn` is true if at least +% one of the guards `G1, G2, ...` evaluates to true. +is_pet(A) when is_dog(A); is_cat(A) -> true; +is_pet(A) -> false. + +% Records provide a method for associating a name with a particular element in a +% tuple. +% Record definitions can be included in Erlang source code files or put in files +% with the extension `.hrl`, which are then included by Erlang source code +% files. +-record(todo, { + status = reminder, % Default value + who = joe, + text +}). + +% We have to read the record definitions into the shell before we can define a +% record. We use the shell function `rr` (short for read records) to do this. +rr("records.hrl"). % [todo] + +% Creating and updating records: +X = #todo{}. +% #todo{status = reminder, who = joe, text = undefined} +X1 = #todo{status = urgent, text = "Fix errata in book"}. +% #todo{status = urgent, who = joe, text = "Fix errata in book"} +X2 = X1#todo{status = done}. +% #todo{status = done,who = joe,text = "Fix errata in book"} + +% `case` expressions. +% `filter` returns a list of all those elements `X` in `L` for which `P(X)` is +% true. +filter(P, [H|T]) -> + case P(H) of + true -> [H|filter(P, T)]; + false -> filter(P, T) + end; +filter(P, []) -> []. + +% `if` expressions. +max(X, Y) -> + if + X > Y -> X; + X < Y -> Y; + true -> nil; + end. + +% Warning: at least one of the guards in the if expression must evaluate to true; +% otherwise, an exception will be raised. + + +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +%% 3. Exceptions. +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +% Exceptions are raised by the system when internal errors are encountered or +% explicitly in code by calling `throw(Exception)`, `exit(Exception)` or +% `erlang:error(Exception)`. +generate_exception(1) -> a; +generate_exception(2) -> throw(a); +generate_exception(3) -> exit(a); +generate_exception(4) -> {'EXIT', a}; +generate_exception(5) -> erlang:error(a). + +% Erlang has two methods of catching an exception. One is to enclose the call to +% the function, which raised the exception within a `try...catch` expression. +catcher(N) -> + try generate_exception(N) of + Val -> {N, normal, Val} + catch + throw:X -> {N, caught, thrown, X}; + exit:X -> {N, caught, exited, X}; + error:X -> {N, caught, error, X} + end. + +% The other is to enclose the call in a `catch` expression. When you catch an +% exception, it is converted into a tuple that describes the error. +catcher(N) -> catch generate_exception(N). + +``` + +## References + +* "Programming Erlang: Software for a Concurrent World" by Joe Armstrong +* [Erlang - Programming Rules and Conventions](http://www.erlang.se/doc/programming_rules.shtml) +* [Erlang/OTP Documentation](http://www.erlang.org/doc/) diff --git a/file.erb b/file.erb new file mode 100644 index 00000000..5f162aa5 --- /dev/null +++ b/file.erb @@ -0,0 +1 @@ +<%= rawcode %> diff --git a/fsharp.html.markdown b/fsharp.html.markdown new file mode 100644 index 00000000..b1860372 --- /dev/null +++ b/fsharp.html.markdown @@ -0,0 +1,633 @@ +--- +language: F# +author: Scott Wlaschin +author_url: http://fsharpforfunandprofit.com/ +filename: learnfsharp.fs +--- + +F# is a general purpose functional/OO programming language. It's free and open source, and runs on Linux, Mac, Windows and more. + +It has a powerful type system that traps many errors at compile time, but it uses type inference so that it reads more like a dynamic language. + +The syntax of F# is different from C-style languages: + +* Curly braces are not used to delimit blocks of code. Instead, indentation is used (like Python). +* Whitespace is used to separate parameters rather than commas. + +If you want to try out the code below, you can go to [tryfsharp.org](http://www.tryfsharp.org/Create) and paste it into an interactive REPL. + +```csharp + +// single line comments use a double slash +(* multi line comments use (* . . . *) pair + +-end of multi line comment- *) + +// ================================================ +// Basic Syntax +// ================================================ + +// ------ "Variables" (but not really) ------ +// The "let" keyword defines an (immutable) value +let myInt = 5 +let myFloat = 3.14 +let myString = "hello" //note that no types needed + +// ------ Lists ------ +let twoToFive = [2;3;4;5] // Square brackets create a list with + // semicolon delimiters. +let oneToFive = 1 :: twoToFive // :: creates list with new 1st element +// The result is [1;2;3;4;5] +let zeroToFive = [0;1] @ twoToFive // @ concats two lists + +// IMPORTANT: commas are never used as delimiters, only semicolons! + +// ------ Functions ------ +// The "let" keyword also defines a named function. +let square x = x * x // Note that no parens are used. +square 3 // Now run the function. Again, no parens. + +let add x y = x + y // don't use add (x,y)! It means something + // completely different. +add 2 3 // Now run the function. + +// to define a multiline function, just use indents. No semicolons needed. +let evens list = + let isEven x = x%2 = 0 // Define "isEven" as a sub function + List.filter isEven list // List.filter is a library function + // with two parameters: a boolean function + // and a list to work on + +evens oneToFive // Now run the function + +// You can use parens to clarify precedence. In this example, +// do "map" first, with two args, then do "sum" on the result. +// Without the parens, "List.map" would be passed as an arg to List.sum +let sumOfSquaresTo100 = + List.sum ( List.map square [1..100] ) + +// You can pipe the output of one operation to the next using "|>" +// Piping data around is very common in F#, similar to UNIX pipes. + +// Here is the same sumOfSquares function written using pipes +let sumOfSquaresTo100piped = + [1..100] |> List.map square |> List.sum // "square" was defined earlier + +// you can define lambdas (anonymous functions) using the "fun" keyword +let sumOfSquaresTo100withFun = + [1..100] |> List.map (fun x -> x*x) |> List.sum + +// In F# there is no "return" keyword. A function always +// returns the value of the last expression used. + +// ------ Pattern Matching ------ +// Match..with.. is a supercharged case/switch statement. +let simplePatternMatch = + let x = "a" + match x with + | "a" -> printfn "x is a" + | "b" -> printfn "x is b" + | _ -> printfn "x is something else" // underscore matches anything + +// F# doesn't allow nulls by default -- you must use an Option type +// and then pattern match. +// Some(..) and None are roughly analogous to Nullable wrappers +let validValue = Some(99) +let invalidValue = None + +// In this example, match..with matches the "Some" and the "None", +// and also unpacks the value in the "Some" at the same time. +let optionPatternMatch input = + match input with + | Some i -> printfn "input is an int=%d" i + | None -> printfn "input is missing" + +optionPatternMatch validValue +optionPatternMatch invalidValue + +// ------ Printing ------ +// The printf/printfn functions are similar to the +// Console.Write/WriteLine functions in C#. +printfn "Printing an int %i, a float %f, a bool %b" 1 2.0 true +printfn "A string %s, and something generic %A" "hello" [1;2;3;4] + +// There are also sprintf/sprintfn functions for formatting data +// into a string, similar to String.Format in C#. + +// ================================================ +// More on functions +// ================================================ + +// F# is a true functional language -- functions are first +// class entities and can be combined easy to make powerful +// constructs + +// Modules are used to group functions together +// Indentation is needed for each nested module. +module FunctionExamples = + + // define a simple adding function + let add x y = x + y + + // basic usage of a function + let a = add 1 2 + printfn "1+2 = %i" a + + // partial application to "bake in" parameters + let add42 = add 42 + let b = add42 1 + printfn "42+1 = %i" b + + // composition to combine functions + let add1 = add 1 + let add2 = add 2 + let add3 = add1 >> add2 + let c = add3 7 + printfn "3+7 = %i" c + + // higher order functions + [1..10] |> List.map add3 |> printfn "new list is %A" + + // lists of functions, and more + let add6 = [add1; add2; add3] |> List.reduce (>>) + let d = add6 7 + printfn "1+2+3+7 = %i" d + +// ================================================ +// Lists and collection +// ================================================ + +// There are three types of ordered collection: +// * Lists are most basic immutable collection. +// * Arrays are mutable and more efficient when needed. +// * Sequences are lazy and infinite (e.g. an enumerator). +// +// Other collections include immutable maps and sets +// plus all the standard .NET collections + +module ListExamples = + + // lists use square brackets + let list1 = ["a";"b"] + let list2 = "c" :: list1 // :: is prepending + let list3 = list1 @ list2 // @ is concat + + // list comprehensions (aka generators) + let squares = [for i in 1..10 do yield i*i] + + // prime number generator + let rec sieve = function + | (p::xs) -> p :: sieve [ for x in xs do if x % p > 0 then yield x ] + | [] -> [] + let primes = sieve [2..50] + printfn "%A" primes + + // pattern matching for lists + let listMatcher aList = + match aList with + | [] -> printfn "the list is empty" + | [first] -> printfn "the list has one element %A " first + | [first; second] -> printfn "list is %A and %A" first second + | _ -> printfn "the list has more than two elements" + + listMatcher [1;2;3;4] + listMatcher [1;2] + listMatcher [1] + listMatcher [] + + // recursion using lists + let rec sum aList = + match aList with + | [] -> 0 + | x::xs -> x + sum xs + sum [1..10] + + // ----------------------------------------- + // Standard library functions + // ----------------------------------------- + + // map + let add3 x = x + 3 + [1..10] |> List.map add3 + + // filter + let even x = x % 2 = 0 + [1..10] |> List.filter even + + // many more -- see documentation + +module ArrayExamples = + + // arrays use square brackets with bar + let array1 = [| "a";"b" |] + let first = array1.[0] // indexed access using dot + + // pattern matching for arrays is same as for lists + let arrayMatcher aList = + match aList with + | [| |] -> printfn "the array is empty" + | [| first |] -> printfn "the array has one element %A " first + | [| first; second |] -> printfn "array is %A and %A" first second + | _ -> printfn "the array has more than two elements" + + arrayMatcher [| 1;2;3;4 |] + + // Standard library functions just as for List + + [| 1..10 |] + |> Array.map (fun i -> i+3) + |> Array.filter (fun i -> i%2 = 0) + |> Array.iter (printfn "value is %i. ") + + +module SequenceExamples = + + // sequences use curly braces + let seq1 = seq { yield "a"; yield "b" } + + // sequences can use yield and + // can contain subsequences + let strange = seq { + // "yield! adds one element + yield 1; yield 2; + + // "yield!" adds a whole subsequence + yield! [5..10] + yield! seq { + for i in 1..10 do + if i%2 = 0 then yield i }} + // test + strange |> Seq.toList + + + // Sequences can be created using "unfold" + // Here's the fibonacci series + let fib = Seq.unfold (fun (fst,snd) -> + Some(fst + snd, (snd, fst + snd))) (0,1) + + // test + let fib10 = fib |> Seq.take 10 |> Seq.toList + printf "first 10 fibs are %A" fib10 + + +// ================================================ +// Data Types +// ================================================ + +module DataTypeExamples = + + // All data is immutable by default + + // Tuples are quick 'n easy anonymous types + // -- Use a comma to create a tuple + let twoTuple = 1,2 + let threeTuple = "a",2,true + + // Pattern match to unpack + let x,y = twoTuple //sets x=1 y=2 + + // ------------------------------------ + // Record types have named fields + // ------------------------------------ + + // Use "type" with curly braces to define a record type + type Person = {First:string; Last:string} + + // Use "let" with curly braces to create a record + let person1 = {First="John"; Last="Doe"} + + // Pattern match to unpack + let {First=first} = person1 //sets first="john" + + // ------------------------------------ + // Union types (aka variants) have a set of choices + // Only case can be valid at a time. + // ------------------------------------ + + // Use "type" with bar/pipe to define a union type + type Temp = + | DegreesC of float + | DegreesF of float + + // Use one of the cases to create one + let temp1 = DegreesF 98.6 + let temp2 = DegreesC 37.0 + + // Pattern match on all cases to unpack + let printTemp = function + | DegreesC t -> printfn "%f degC" t + | DegreesF t -> printfn "%f degF" t + + printTemp temp1 + printTemp temp2 + + // ------------------------------------ + // Recursive types + // ------------------------------------ + + // Types can be combined recursively in complex ways + // without having to create subclasses + type Employee = + | Worker of Person + | Manager of Employee list + + let jdoe = {First="John";Last="Doe"} + let worker = Worker jdoe + + // ------------------------------------ + // Modelling with types + // ------------------------------------ + + // Union types are great for modelling state without using flags + type EmailAddress = + | ValidEmailAddress of string + | InvalidEmailAddress of string + + let trySendEmail email = + match email with // use pattern matching + | ValidEmailAddress address -> () // send + | InvalidEmailAddress address -> () // dont send + + // The combination of union types and record types together + // provide a great foundation for domain driven design. + // You can create hundreds of little types that accurately + // reflect the domain. + + type CartItem = { ProductCode: string; Qty: int } + type Payment = Payment of float + type ActiveCartData = { UnpaidItems: CartItem list } + type PaidCartData = { PaidItems: CartItem list; Payment: Payment} + + type ShoppingCart = + | EmptyCart // no data + | ActiveCart of ActiveCartData + | PaidCart of PaidCartData + + // ------------------------------------ + // Built in behavior for types + // ------------------------------------ + + // Core types have useful "out-of-the-box" behavior, no coding needed. + // * Immutability + // * Pretty printing when debugging + // * Equality and comparison + // * Serialization + + // Pretty printing using %A + printfn "twoTuple=%A,\nPerson=%A,\nTemp=%A,\nEmployee=%A" + twoTuple person1 temp1 worker + + // Equality and comparison built in. + // Here's an example with cards. + type Suit = Club | Diamond | Spade | Heart + type Rank = Two | Three | Four | Five | Six | Seven | Eight + | Nine | Ten | Jack | Queen | King | Ace + + let hand = [ Club,Ace; Heart,Three; Heart,Ace; + Spade,Jack; Diamond,Two; Diamond,Ace ] + + // sorting + List.sort hand |> printfn "sorted hand is (low to high) %A" + List.max hand |> printfn "high card is %A" + List.min hand |> printfn "low card is %A" + + +// ================================================ +// Active patterns +// ================================================ + +module ActivePatternExamples = + + // F# has a special type of pattern matching called "active patterns" + // where the pattern can be parsed or detected dynamically. + + // "banana clips" are the syntax for active patterns + + // for example, define an "active" pattern to match character types... + let (|Digit|Letter|Whitespace|Other|) ch = + if System.Char.IsDigit(ch) then Digit + else if System.Char.IsLetter(ch) then Letter + else if System.Char.IsWhiteSpace(ch) then Whitespace + else Other + + // ... and then use it to make parsing logic much clearer + let printChar ch = + match ch with + | Digit -> printfn "%c is a Digit" ch + | Letter -> printfn "%c is a Letter" ch + | Whitespace -> printfn "%c is a Whitespace" ch + | _ -> printfn "%c is something else" ch + + // print a list + ['a';'b';'1';' ';'-';'c'] |> List.iter printChar + + // ----------------------------------- + // FizzBuzz using active patterns + // ----------------------------------- + + // You can create partial matching patterns as well + // Just use undercore in the defintion, and return Some if matched. + let (|MultOf3|_|) i = if i % 3 = 0 then Some MultOf3 else None + let (|MultOf5|_|) i = if i % 5 = 0 then Some MultOf5 else None + + // the main function + let fizzBuzz i = + match i with + | MultOf3 & MultOf5 -> printf "FizzBuzz, " + | MultOf3 -> printf "Fizz, " + | MultOf5 -> printf "Buzz, " + | _ -> printf "%i, " i + + // test + [1..20] |> List.iter fizzBuzz + +// ================================================ +// Conciseness +// ================================================ + +module AlgorithmExamples = + + // F# has a high signal/noise ratio, so code reads + // almost like the actual algorithm + + // ------ Example: define sumOfSquares function ------ + let sumOfSquares n = + [1..n] // 1) take all the numbers from 1 to n + |> List.map square // 2) square each one + |> List.sum // 3) sum the results + + // test + sumOfSquares 100 |> printfn "Sum of squares = %A" + + // ------ Example: define a sort function ------ + let rec sort list = + match list with + // If the list is empty + | [] -> + [] // return an empty list + // If the list is not empty + | firstElem::otherElements -> // take the first element + let smallerElements = // extract the smaller elements + otherElements // from the remaining ones + |> List.filter (fun e -> e < firstElem) + |> sort // and sort them + let largerElements = // extract the larger ones + otherElements // from the remaining ones + |> List.filter (fun e -> e >= firstElem) + |> sort // and sort them + // Combine the 3 parts into a new list and return it + List.concat [smallerElements; [firstElem]; largerElements] + + // test + sort [1;5;23;18;9;1;3] |> printfn "Sorted = %A" + +// ================================================ +// Asynchronous Code +// ================================================ + +module AsyncExample = + + // F# has built-in features to help with async code + // without encountering the "pyramid of doom" + // + // The following example downloads a set of web pages in parallel. + + open System.Net + open System + open System.IO + open Microsoft.FSharp.Control.CommonExtensions + + // Fetch the contents of a URL asynchronously + let fetchUrlAsync url = + async { // "async" keyword and curly braces + // creates an "async" object + let req = WebRequest.Create(Uri(url)) + use! resp = req.AsyncGetResponse() + // use! is async assignment + use stream = resp.GetResponseStream() + // "use" triggers automatic close() + // on resource at end of scope + use reader = new IO.StreamReader(stream) + let html = reader.ReadToEnd() + printfn "finished downloading %s" url + } + + // a list of sites to fetch + let sites = ["http://www.bing.com"; + "http://www.google.com"; + "http://www.microsoft.com"; + "http://www.amazon.com"; + "http://www.yahoo.com"] + + // do it + sites + |> List.map fetchUrlAsync // make a list of async tasks + |> Async.Parallel // set up the tasks to run in parallel + |> Async.RunSynchronously // start them off + +// ================================================ +// .NET compatability +// ================================================ + +module NetCompatibilityExamples = + + // F# can do almost everything C# can do, and it integrates + // seamlessly with .NET or Mono libraries. + + // ------- work with existing library functions ------- + + let (i1success,i1) = System.Int32.TryParse("123"); + if i1success then printfn "parsed as %i" i1 else printfn "parse failed" + + // ------- Implement interfaces on the fly! ------- + + // create a new object that implements IDisposable + let makeResource name = + { new System.IDisposable + with member this.Dispose() = printfn "%s disposed" name } + + let useAndDisposeResources = + use r1 = makeResource "first resource" + printfn "using first resource" + for i in [1..3] do + let resourceName = sprintf "\tinner resource %d" i + use temp = makeResource resourceName + printfn "\tdo something with %s" resourceName + use r2 = makeResource "second resource" + printfn "using second resource" + printfn "done." + + // ------- Object oriented code ------- + + // F# is also a fully fledged OO language. + // It supports classes, inheritance, virtual methods, etc. + + // interface with generic type + type IEnumerator<'a> = + abstract member Current : 'a + abstract MoveNext : unit -> bool + + // abstract base class with virtual methods + [<AbstractClass>] + type Shape() = + //readonly properties + abstract member Width : int with get + abstract member Height : int with get + //non-virtual method + member this.BoundingArea = this.Height * this.Width + //virtual method with base implementation + abstract member Print : unit -> unit + default this.Print () = printfn "I'm a shape" + + // concrete class that inherits from base class and overrides + type Rectangle(x:int, y:int) = + inherit Shape() + override this.Width = x + override this.Height = y + override this.Print () = printfn "I'm a Rectangle" + + //test + let r = Rectangle(2,3) + printfn "The width is %i" r.Width + printfn "The area is %i" r.BoundingArea + r.Print() + + // ------- extension methods ------- + + //Just as in C#, F# can extend existing classes with extension methods. + type System.String with + member this.StartsWithA = this.StartsWith "A" + + //test + let s = "Alice" + printfn "'%s' starts with an 'A' = %A" s s.StartsWithA + + // ------- events ------- + + type MyButton() = + let clickEvent = new Event<_>() + + [<CLIEvent>] + member this.OnClick = clickEvent.Publish + + member this.TestEvent(arg) = + clickEvent.Trigger(this, arg) + + // test + let myButton = new MyButton() + myButton.OnClick.Add(fun (sender, arg) -> + printfn "Click event with arg=%O" arg) + + myButton.TestEvent("Hello World!") + +``` + +## More Information + +For more demonstrations of F#, go to the [Try F#](http://www.tryfsharp.org/Learn) site, or my [why use F#](http://fsharpforfunandprofit.com/why-use-fsharp/) series. + +Read more about F# at [fsharp.org](http://fsharp.org/). + + + + diff --git a/haskell.html.markdown b/haskell.html.markdown new file mode 100644 index 00000000..840569fb --- /dev/null +++ b/haskell.html.markdown @@ -0,0 +1,361 @@ +--- +language: haskell +author: Adit Bhargava +author_url: http://adit.io +--- + +Haskell was designed as a practical, purely functional programming language. It's famous for +its monads and its type system, but I keep coming back to it because of its elegance. Haskell +makes coding a real joy for me. + +```haskell +-- Single line comments start with two dashes. +{- Multiline comments can be enclosed +in a block like this. +-} + +---------------------------------------------------- +-- 1. Primitive Datatypes and Operators +---------------------------------------------------- + +-- You have numbers +3 -- 3 + +-- Math is what you would expect +1 + 1 -- 2 +8 - 1 -- 7 +10 * 2 -- 20 +35 / 5 -- 7.0 + +-- Division is not integer division by default +35 / 4 -- 8.75 + +-- integer division +35 `div` 4 -- 8 + +-- Boolean values are primitives +True +False + +-- Boolean operations +not True -- False +not False -- True +1 == 1 -- True +1 /= 1 -- False +1 < 10 -- True + +-- In the above examples, `not` is a function that takes one value. +-- Haskell doesn't need parentheses for function calls...all the arguments +-- are just listed after the function. So the general pattern is: +-- func arg1 arg2 arg3... +-- See the section on functions for information on how to write your own. + +-- Strings and characters +"This is a string." +'a' -- character +'You cant use single quotes for strings.' -- error! + +-- Strings can be concatenated +"Hello " ++ "world!" -- "Hello world!" + +-- A string is a list of characters +"This is a string" !! 0 -- 'T' + + +---------------------------------------------------- +-- Lists and Tuples +---------------------------------------------------- + +-- Every element in a list must have the same type. +-- Two lists that are the same +[1, 2, 3, 4, 5] +[1..5] + +-- You can also have infinite lists in Haskell! +[1..] -- a list of all the natural numbers + +-- Infinite lists work because Haskell has "lazy evaluation". This means +-- that Haskell only evaluates things when it needs to. So you can ask for +-- the 1000th element of your list and Haskell will give it to you: + +[1..] !! 999 -- 1000 + +-- And now Haskell has evaluated elements 1 - 1000 of this list...but the +-- rest of the elements of this "infinite" list don't exist yet! Haskell won't +-- actually evaluate them until it needs to. + + - joining two lists +[1..5] ++ [6..10] + +-- adding to the head of a list +0:[1..5] -- [0, 1, 2, 3, 4, 5] + +-- indexing into a list +[0..] !! 5 -- 5 + +-- more list operations +head [1..5] -- 1 +tail [1..5] -- [2, 3, 4, 5] +init [1..5] -- [1, 2, 3, 4] +last [1..5] -- 5 + +-- list comprehensions +[x*2 | x <- [1..5]] -- [2, 4, 6, 8, 10] + +-- with a conditional +[x*2 | x <- [1..5], x*2 > 4] -- [6, 8, 10] + +-- Every element in a tuple can be a different type, but a tuple has a +-- fixed length. +-- A tuple: +("haskell", 1) + +-- accessing elements of a tuple +fst ("haskell", 1) -- "haskell" +snd ("haskell", 1) -- 1 + +---------------------------------------------------- +-- 3. Functions +---------------------------------------------------- +-- A simple function that takes two variables +add a b = a + b + +-- Note that if you are using ghci (the Haskell interpreter) +-- You'll need to use `let`, i.e. +-- let add a b = a + b + +-- Using the function +add 1 2 -- 3 + +-- You can also put the function name between the two arguments +-- with backticks: +1 `add` 2 -- 3 + +-- You can also define functions that have no characters! This lets +-- you define your own operators! Here's an operator that does +-- integer division +(//) a b = a `div` b +35 // 4 -- 8 + +-- Guards: an easy way to do branching in functions +fib x + | x < 2 = x + | otherwise = fib (x - 1) + fib (x - 2) + +-- Pattern matching is similar. Here we have given three different +-- definitions for fib. Haskell will automatically call the first +-- function that matches the pattern of the value. +fib 1 = 1 +fib 2 = 2 +fib x = fib (x - 1) + fib (x - 2) + +-- Pattern matching on tuples: +foo (x, y) = (x + 1, y + 2) + +-- Pattern matching on lists. Here `x` is the first element +-- in the list, and `xs` is the rest of the list. We can write +-- our own map function: +myMap func [] = [] +myMap func (x:xs) = func x:(myMap func xs) + +-- Anonymous functions are created with a backslash followed by +-- all the arguments. +myMap (\x -> x + 2) [1..5] -- [3, 4, 5, 6, 7] + +-- using fold (called `inject` in some languages) with an anonymous +-- function. foldl1 means fold left, and use the first value in the +-- list as the initial value for the accumulator. +foldl1 (\acc x -> acc + x) [1..5] -- 15 + +---------------------------------------------------- +-- 4. More functions +---------------------------------------------------- + +-- currying: if you don't pass in all the arguments to a function, +-- it gets "curried". That means it returns a function that takes the +-- rest of the arguments. + +add a b = a + b +foo = add 10 -- foo is now a function that takes a number and adds 10 to it +foo 5 -- 15 + +-- Another way to write the same thing +foo = (+10) +foo 5 -- 15 + +-- function composition +-- the (.) function chains functions together. +-- For example, here foo is a function that takes a value. It adds 10 to it, +-- multiplies the result of that by 5, and then returns the final value. +foo = (*5) . (+10) + +-- (5 + 10) * 5 = 75 +foo 5 -- 75 + +-- fixing precedence +-- Haskell has another function called `$`. This changes the precedence +-- so that everything to the left of it gets computed first and then applied +-- to everything on the right. You can use `.` and `$` to get rid of a lot +-- of parentheses: + +-- before +(even (fib 7)) -- true + +-- after +even . fib $ 7 -- true + +---------------------------------------------------- +-- 5. Type signatures +---------------------------------------------------- + +-- Haskell has a very strong type system, and everything has a type signature. + +-- Some basic types: +5 :: Integer +"hello" :: String +True :: Bool + +-- Functions have types too. +-- `not` takes a boolean and returns a boolean: +-- not :: Bool -> Bool + +-- Here's a function that takes two arguments: +-- add :: Integer -> Integer -> Integer + +-- When you define a value, it's good practice to write its type above it: +double :: Integer -> Integer +double x = x * 2 + +---------------------------------------------------- +-- 6. Control Flow and If Statements +---------------------------------------------------- + +-- if statements +haskell = if 1 == 1 then "awesome" else "awful" -- haskell = "awesome" + +-- if statements can be on multiple lines too, indentation is important +haskell = if 1 == 1 + then "awesome" + else "awful" + +-- case statements: Here's how you could parse command line arguments +case args of + "help" -> printHelp + "start" -> startProgram + _ -> putStrLn "bad args" + +-- Haskell doesn't have loops because it uses recursion instead. +-- map applies a function over every element in an array + +map (*2) [1..5] -- [2, 4, 6, 8, 10] + +-- you can make a for function using map +for array func = map func array + +-- and then use it +for [0..5] $ \i -> show i + +-- we could've written that like this too: +for [0..5] show + +-- You can use foldl or foldr to reduce a list +-- foldl <fn> <initial value> <list> +foldl (\x y -> 2*x + y) 4 [1,2,3] -- 43 + +-- This is the same as +(2 * (2 * (2 * 4 + 1) + 2) + 3) + +-- foldl is left-handed, foldr is right- +foldr (\x y -> 2*x + y) 4 [1,2,3] -- 16 + +-- This is now the same as +(2 * 3 + (2 * 2 + (2 * 1 + 4) + +---------------------------------------------------- +-- 7. Data Types +---------------------------------------------------- + +-- Here's how you make your own data type in Haskell + +data Color = Red | Blue | Green + +-- Now you can use it in a function: + +say :: Color -> IO String +say Red = putStrLn "You are Red!" +say Blue = putStrLn "You are Blue!" +say Green = putStrLn "You are Green!" + +-- Your data types can have parameters too: + +data Maybe a = Nothing | Just a + +-- These are all of type Maybe +Nothing +Just "hello" +Just 1 + +---------------------------------------------------- +-- 8. Haskell IO +---------------------------------------------------- + +-- While IO can't be explained fully without explaining monads, +-- it is not hard to explain enough to get going. + +-- An `IO a` value is an IO action: you can chain them with do blocks +action :: IO String +action = do + putStrLn "This is a line. Duh" + input <- getLine -- this gets a line and gives it the name "input" + input2 <- getLine + return (input1 ++ "\n" ++ input2) -- This is the result of the whole action + +-- This didn't actually do anything. When a haskell program is executed +-- an IO action called "main" is read and interpreted. + +main = do + putStrLn "Our first program. How exciting!" + result <- action -- our defined action is just like the default ones + putStrLn result + putStrLn "This was all, folks!" + +-- Haskell does IO through a monad because this allows it to be a purely +-- functional language. Our `action` function had a type signature of `IO String`. +-- In general any function that interacts with the outside world (i.e. does IO) +-- gets marked as `IO` in its type signature. This lets us reason about what +-- functions are "pure" (don't interact with the outside world or modify state) +-- and what functions aren't. + +-- This is a powerful feature, because it's easy to run pure functions concurrently +-- so concurrency in Haskell is very easy. + + +---------------------------------------------------- +-- 9. The Haskell REPL +---------------------------------------------------- + +-- Start the repl by typing `ghci`. +-- Now you can type in Haskell code. Any new values +-- need to be created with `let`: + +let foo = 5 + +-- You can see the type of any value with `:t`: + +>:t foo +foo :: Integer +``` + +There's a lot more to Haskell, including typeclasses and monads. These are the big ideas that make Haskell such fun to code in. I'll leave you with one final Haskell example: an implementation of quicksort in Haskell: + +```haskell +qsort [] = [] +qsort (p:xs) = qsort lesser ++ [p] ++ qsort greater + where lesser = filter (< p) xs + greater = filter (>= p) xs +``` + +Haskell is easy to install. Get it [here](http://www.haskell.org/platform/). + +You can find a much gentler introduction from the excellent [Learn you a Haskell](http://learnyouahaskell.com/) + diff --git a/java.html.markdown b/java.html.markdown new file mode 100644 index 00000000..8ba48d73 --- /dev/null +++ b/java.html.markdown @@ -0,0 +1,370 @@ +--- + +language: java + +author: Jake Prather + +author_url: http://github.com/JakeHP + +filename: LearnJava.java + +--- + +Java is a general-purpose, concurrent, class-based, object-oriented computer programming language. +[Read more here.](http://docs.oracle.com/javase/tutorial/java/index.html) + +```java +// Single-line comments start with // +/* +Multi-line comments look like this. +*/ + +// Import ArrayList class inside of the java.util package +import java.util.ArrayList; +// Import all classes inside of java.security package +import java.security.*; + +// Each .java file contains one public class, with the same name as the file. +public class LearnJava { + + // A program must have a main method as an entry point + public static void main (String[] args) { + + // Use System.out.println to print lines + System.out.println("Hello World!"); + System.out.println( + "Integer: " + 10 + + " Double: " + 3.14 + + " Boolean: " + true); + + // To print without a newline, use System.out.print + System.out.print("Hello "); + System.out.print("World"); + + + /////////////////////////////////////// + // Types & Variables + /////////////////////////////////////// + + // Declare a variable using <type> <name> [ + // Byte - 8-bit signed two's complement integer + // (-128 <= byte <= 127) + byte fooByte = 100; + + // Short - 16-bit signed two's complement integer + // (-32,768 <= short <= 32,767) + short fooShort = 10000; + + // Integer - 32-bit signed two's complement integer + // (-2,147,483,648 <= int <= 2,147,483,647) + int fooInt = 1; + + // Long - 64-bit signed two's complement integer + // (-9,223,372,036,854,775,808 <= long <= 9,223,372,036,854,775,807) + long fooLong = 100000L; + + // (Java has no unsigned types) + + // Float - Single-precision 32-bit IEEE 754 Floating Point + float fooFloat = 234.5f; + + // Double - Double-precision 64-bit IEEE 754 Floating Point + double fooDouble = 123.4; + + // Boolean - true & false + boolean fooBoolean = true; + boolean barBoolean = false; + + // Char - A single 16-bit Unicode character + char fooChar = 'A'; + + // Use final to make a variable immutable + final int HOURS_I_WORK_PER_WEEK = 9001; + + // Strings + String fooString = "My String Is Here!"; + + // \n is an escaped character that starts a new line + String barString = "Printing on a new line?\nNo Problem!"; + System.out.println(fooString); + System.out.println(barString); + + // Arrays + //The array size must be decided upon declaration + //The format for declaring an array is follows: + //<datatype> [] <var name> = new <datatype>[<array size>]; + int [] intArray = new int[10]; + String [] stringArray = new String[1]; + boolean [] booleanArray = new boolean[100]; + + // Another way to declare & initialize an array + int [] y = {9000, 1000, 1337}; + + // Indexing an array - Accessing an element + System.out.println("intArray @ 0: " + intArray[0]); + + // Arrays are zero-indexed and mutable. + intArray[1] = 1; + System.out.println("intArray @ 1: " + intArray[1]); // => 1 + + // Others to check out + // ArrayLists - Like arrays except more functionality is offered, + // and the size is mutable + // LinkedLists + // Maps + // HashMaps + + /////////////////////////////////////// + // Operators + /////////////////////////////////////// + System.out.println("\n->Operators"); + + int i1 = 1, i2 = 2; // Shorthand for multiple declarations + + // Arithmetic is straightforward + System.out.println("1+2 = " + (i1 + i2)); // => 3 + System.out.println("2-1 = " + (i2 - i1)); // => 1 + System.out.println("2*1 = " + (i2 * i1)); // => 2 + System.out.println("1/2 = " + (i1 / i2)); // => 0 (0.5 truncated down) + + // Modulo + System.out.println("11%3 = "+(11 % 3)); // => 2 + + // Comparison operators + System.out.println("3 == 2? " + (3 == 2)); // => 0 (false) + System.out.println("3 != 2? " + (3 != 2)); // => 1 (true) + System.out.println("3 > 2? " + (3 > 2)); // => 1 + System.out.println("3 < 2? " + (3 < 2)); // => 0 + System.out.println("2 <= 2? " + (2 <= 2)); // => 1 + System.out.println("2 >= 2? " + (2 >= 2)); // => 1 + + // Bitwise operators! + /* + ~ Unary bitwise complement + << Signed left shift + >> Signed right shift + >>> Unsigned right shift + & Bitwise AND + ^ Bitwise exclusive OR + | Bitwise inclusive OR + */ + + // Incrementations + int i=0; + System.out.println("\n->Inc/Dec-rementation"); + System.out.println(i++); //i = 1. Post-Incrementation + System.out.println(++i); //i = 2. Pre-Incrementation + System.out.println(i--); //i = 1. Post-Decrementation + System.out.println(--i); //i = 0. Pre-Decrementation + + /////////////////////////////////////// + // Control Structures + /////////////////////////////////////// + System.out.println("\n->Control Structures"); + + // If statements are c-like + if (false){ + System.out.println("I never run"); + }else if (false) { + System.out.println("I am also never run"); + } else { + System.out.println("I print"); + } + + // While loop + int fooWhile = 0; + while(fooWhile < 100) + { + //System.out.println(fooWhile); + //Increment the counter + //Iterated 99 times, fooWhile 0->99 + fooWhile++; + } + System.out.println("fooWhile Value: " + fooWhile); + + // Do While Loop + int fooDoWhile = 0; + do + { + //System.out.println(fooDoWhile); + //Increment the counter + //Iterated 99 times, fooDoWhile 0->99 + fooDoWhile++; + }while(fooDoWhile < 100); + System.out.println("fooDoWhile Value: " + fooDoWhile); + + // For Loop + int fooFor; + //for loop structure => for(<start_statement>; <conditional>; <step>) + for(fooFor=0; fooFor<10; fooFor++){ + //System.out.println(fooFor); + //Iterated 10 times, fooFor 0->9 + } + System.out.println("fooFor Value: " + fooFor); + + // Switch Case + int month = 3; + String monthString; + switch (month){ + case 1: monthString = "January"; + break; + case 2: monthString = "February"; + break; + case 3: monthString = "March"; + break; + default: monthString = "Some other month"; + break; + } + System.out.println("Switch Case Result: " + monthString); + + + /////////////////////////////////////// + // Converting Data Types And Typcasting + /////////////////////////////////////// + + // Converting data + + // Convert String To Integer + Integer.parseInt("123");//returns an integer version of "123" + + // Convert Integer To String + Integer.toString(123);//returns a string version of 123 + + // For other conversions check out the following classes: + // Double + // Long + // String + + // Typecasting + // You can also cast java objects, there's a lot of details and + // deals with some more intermediate concepts. + // Feel free to check it out here: + // http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html + + + /////////////////////////////////////// + // Classes And Functions + /////////////////////////////////////// + + System.out.println("\n->Classes & Functions"); + + // (definition of the Bicycle class follows) + + // Use new to instantiate a class + Bicycle trek = new Bicycle(); + + // Call object methods + trek.speedUp(3); + trek.setCadence(100); + + // toString is a convention + System.out.println("trek info: " + trek.toString()); + + } // End main method +} // End LearnJava class + + +// You can include other, non-public classes in a .java file + + +// Class Declaration Syntax: +// <public/private/protected> class <class name>{ +// //data fields, constructors, functions all inside +// } + +class Bicycle { + + // Bicycle's Fields/Variables + public int cadence; // Public: Can be accessed from anywhere + private int speed; // Private: Only accessable from within the class + protected int gear; // Protected: Accessible from the class and subclasses + + // Constructors are a way of creating classes + // This is a default constructor + public Bicycle() { + gear = 1; + cadence = 50; + speed = 5; + } + + // This is a specified constructor (it contains arguments) + public Bicycle(int startCadence, int startSpeed, int startGear) { + gear = startGear; + cadence = startCadence; + speed = startSpeed; + } + + // Function Syntax: + // <public/private/protected> <return type> <function name>(<args>) + + // Java classes often implement getters and setters for their fields + + // Method declaration syntax: + // <scope> <return type> <method name>(<args>) + public int getCadence() { + return cadence; + } + + // void methods require no return statement + public void setCadence(int newValue) { + cadence = newValue; + } + + public void setGear(int newValue) { + gear = newValue; + } + + public void speedUp(int increment) { + speed += increment; + } + + public void slowDown(int decrement) { + speed -= decrement; + } + + public String toString() { + return "gear: "+Integer.toString(gear)+ + " cadence: "+Integer.toString(cadence)+ + " speed: "+Integer.toString(speed); + } +} // end class Bicycle + +// PennyFarthing is a subclass of Bicycle +class PennyFarthing extends Bicycle { + // (Penny Farthings are those bicycles with the big front wheel. + // They have no gears.) + + public PennyFarthing(int startCadence, int startSpeed){ + // Call the parent constructor with super + super(startCadence, startSpeed, 0); + } + + // You should mark a method you're overriding with an @annotation + @Override + public void setGear(int gear) { + gear = 0; + } + +} + +``` + +## Further Reading + +Other Topics To Research: + +* [Inheritance](http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html) + +* [Polymorphism](http://docs.oracle.com/javase/tutorial/java/IandI/polymorphism.html) + +* [Abstraction](http://docs.oracle.com/javase/tutorial/java/IandI/abstract.html) + +* [Exceptions](http://docs.oracle.com/javase/tutorial/essential/exceptions/index.html) + +* [Interfaces](http://docs.oracle.com/javase/tutorial/java/IandI/createinterface.html) + +* [Generics](http://docs.oracle.com/javase/tutorial/java/generics/index.html) + +* [Java Code Conventions](http://www.oracle.com/technetwork/java/codeconv-138413.html) + +* The links provided are just to get an understanding of the topic, feel free to google and find specific examples diff --git a/julia.html.markdown b/julia.html.markdown new file mode 100644 index 00000000..6c719b5c --- /dev/null +++ b/julia.html.markdown @@ -0,0 +1,525 @@ +--- +language: julia +author: Leah Hanson +author_url: http://leahhanson.us +filename: learnjulia.jl +--- + +Julia is a new homoiconic functional language focused on technical computing. +While having the full power of homoiconic macros, first-class functions, and low-level control, Julia is as easy to learn and use as Python. + +This is based on the current development version of Julia, as of June 29th, 2013. + +```ruby + +# Single line comments start with a hash. + +#################################################### +## 1. Primitive Datatypes and Operators +#################################################### + +# Everything in Julia is a expression. + +# You have numbers +3 #=> 3 (Int64) +3.2 #=> 3.2 (Float64) +2 + 1im #=> 2 + 1im (Complex{Int64}) +2//3 #=> 2//3 (Rational{Int64}) + +# Math is what you would expect +1 + 1 #=> 2 +8 - 1 #=> 7 +10 * 2 #=> 20 +35 / 5 #=> 7.0 +5 \ 35 #=> 7.0 +5 / 2 #=> 2.5 +div(5, 2) #=> 2 +2 ^ 2 #=> 4 # power, not bitwise xor +12 % 10 #=> 2 + +# Enforce precedence with parentheses +(1 + 3) * 2 #=> 8 + +# Bitwise Operators +~2 #=> -3 # bitwise not +3 & 5 #=> 1 # bitwise and +2 | 4 #=> 6 # bitwise or +2 $ 4 #=> 6 # bitwise xor +2 >>> 1 #=> 1 # logical shift right +2 >> 1 #=> 1 # arithmetic shift right +2 << 1 #=> 4 # logical/arithmetic shift left + +# You can use the bits function to see the binary representation of a number. +bits(12345) +#=> "0000000000000000000000000000000000000000000000000011000000111001" +bits(12345.0) +#=> "0100000011001000000111001000000000000000000000000000000000000000" + +# Boolean values are primitives +true +false + +# Boolean operators +!true #=> false +!false #=> true +1 == 1 #=> true +2 == 1 #=> false +1 != 1 #=> false +2 != 1 #=> true +1 < 10 #=> true +1 > 10 #=> false +2 <= 2 #=> true +2 >= 2 #=> true +# Comparisons can be chained +1 < 2 < 3 #=> true +2 < 3 < 2 #=> false + +# Strings are created with " +"This is a string." + +# Character literals written with ' +'a' + +# A string can be treated like a list of characters +"This is a string"[1] #=> 'T' # Julia indexes from 1 + +# $ can be used for string interpolation: +"2 + 2 = $(2 + 2)" #=> "2 + 2 = 4" +# You can put any Julia expression inside the parenthesis. + +# Another way to format strings is the printf macro. +@printf "%d is less than %f" 4.5 5.3 # 5 is less than 5.300000 + +#################################################### +## 2. Variables and Collections +#################################################### + +# Printing is pretty easy +println("I'm Julia. Nice to meet you!") + +# No need to declare variables before assigning to them. +some_var = 5 #=> 5 +some_var #=> 5 + +# Accessing a previously unassigned variable is an error +try + some_other_var #=> ERROR: some_other_var not defined +catch e + println(e) +end + +# Variable name start with a letter. You can use uppercase letters, digits, +# and exclamation points as well after the initial alphabetic character. +SomeOtherVar123! = 6 #=> 6 + +# You can also use unicode characters +☃ = 8 #=> 8 + +# A note on naming conventions in Julia: +# +# * Names of variables are in lower case, with word separation indicated by +# underscores ('\_'). +# +# * Names of Types begin with a capital letter and word separation is shown +# with CamelCase instead of underscores. +# +# * Names of functions and macros are in lower case, without underscores. +# +# * Functions that modify their inputs have names that end in !. These +# functions are sometimes called mutating functions or in-place functions. + +# Arrays store a sequence of values indexed by integers 1 through n: +a = Int64[] #=> 0-element Int64 Array + +# 1-dimensional array literals can be written with comma-separated values. +b = [4, 5, 6] #=> 3-element Int64 Array: [4, 5, 6] +b[1] #=> 4 +b[end] #=> 6 + +# 2-dimentional arrays use space-separated values and semicolon-separated rows. +matrix = [1 2; 3 4] #=> 2x2 Int64 Array: [1 2; 3 4] + +# Add stuff to the end of a list with push! and append! +push!(a,1) #=> [1] +push!(a,2) #=> [1,2] +push!(a,4) #=> [1,2,4] +push!(a,3) #=> [1,2,4,3] +append!(a,b) #=> [1,2,4,3,4,5,6] + +# Remove from the end with pop +pop!(a) #=> 6 and b is now [4,5] + +# Let's put it back +push!(b,6) # b is now [4,5,6] again. + +a[1] #=> 1 # remember that Julia indexes from 1, not 0! + +# end is a shorthand for the last index. It can be used in any +# indexing expression +a[end] #=> 6 + +# Function names that end in exclamations points indicate that they modify +# their argument. +arr = [5,4,6] #=> 3-element Int64 Array: [5,4,6] +sort(arr) #=> [4,5,6]; arr is still [5,4,6] +sort!(arr) #=> [4,5,6]; arr is now [4,5,6] + +# Looking out of bounds is a BoundsError +try + a[0] #=> ERROR: BoundsError() in getindex at array.jl:270 + a[end+1] #=> ERROR: BoundsError() in getindex at array.jl:270 +catch e + println(e) +end + +# Errors list the line and file they came from, even if it's in the standard +# library. If you built Julia from source, you can look in the folder base +# inside the julia folder to find these files. + +# You can initialize arrays from ranges +a = [1:5] #=> 5-element Int64 Array: [1,2,3,4,5] + +# You can look at ranges with slice syntax. +a[1:3] #=> [1, 2, 3] +a[2:] #=> [2, 3, 4, 5] + +# Remove arbitrary elements from a list with splice! +arr = [3,4,5] +splice!(arr,2) #=> 4 ; arr is now [3,5] + +# Concatenate lists with append! +b = [1,2,3] +append!(a,b) # Now a is [1, 3, 4, 5, 1, 2, 3] + +# Check for existence in a list with contains +contains(a,1) #=> true + +# Examine the length with length +length(a) #=> 7 + +# Tuples are immutable. +tup = (1, 2, 3) #=>(1,2,3) # an (Int64,Int64,Int64) tuple. +tup[1] #=> 1 +try: + tup[0] = 3 #=> ERROR: no method setindex!((Int64,Int64,Int64),Int64,Int64) +catch e + println(e) +end + +# Many list functions also work on tuples +length(tup) #=> 3 +tup[1:2] #=> (1,2) +contains(tup,2) #=> true + +# You can unpack tuples into variables +a, b, c = (1, 2, 3) #=> (1,2,3) # a is now 1, b is now 2 and c is now 3 + +# Tuples are created by default if you leave out the parentheses +d, e, f = 4, 5, 6 #=> (4,5,6) + +# Now look how easy it is to swap two values +e, d = d, e #=> (5,4) # d is now 5 and e is now 4 + + +# Dictionaries store mappings +empty_dict = Dict() #=> Dict{Any,Any}() + +# Here is a prefilled dictionary +filled_dict = ["one"=> 1, "two"=> 2, "three"=> 3] +# => Dict{ASCIIString,Int64} + +# Look up values with [] +filled_dict["one"] #=> 1 + +# Get all keys +keys(filled_dict) +#=> KeyIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2]) +# Note - dictionary keys are not sorted or in the order you inserted them. + +# Get all values +values(filled_dict) +#=> ValueIterator{Dict{ASCIIString,Int64}}(["three"=>3,"one"=>1,"two"=>2]) +# Note - Same as above regarding key ordering. + +# Check for existence of keys in a dictionary with contains, haskey +contains(filled_dict, ("one", 1)) #=> true +contains(filled_dict, ("two", 3)) #=> false +haskey(filled_dict, "one") #=> true +haskey(filled_dict, 1) #=> false + +# Trying to look up a non-existing key will raise an error +try + filled_dict["four"] #=> ERROR: key not found: four in getindex at dict.jl:489 +catch e + println(e) +end + +# Use get method to avoid the error +# get(dictionary,key,default_value) +get(filled_dict,"one",4) #=> 1 +get(filled_dict,"four",4) #=> 4 + +# Sets store sets +empty_set = Set() #=> Set{Any}() +# Initialize a set with a bunch of values +filled_set = Set(1,2,2,3,4) #=> Set{Int64}(1,2,3,4) + +# Add more items to a set +add!(filled_set,5) #=> Set{Int64}(5,4,2,3,1) + +# There are functions for set intersection, union, and difference. +other_set = Set(3, 4, 5, 6) #=> Set{Int64}(6,4,5,3) +intersect(filled_set, other_set) #=> Set{Int64}(3,4,5) +union(filled_set, other_set) #=> Set{Int64}(1,2,3,4,5,6) +setdiff(Set(1,2,3,4),Set(2,3,5)) #=> Set{Int64}(1,4) + +# Check for existence in a set with contains +contains(filled_set,2) #=> true +contains(filled_set,10) #=> false + + +#################################################### +## 3. Control Flow +#################################################### + +# Let's make a variable +some_var = 5 + +# Here is an if statement. Indentation is NOT meaningful in Julia. +# prints "some var is smaller than 10" +if some_var > 10 + println("some_var is totally bigger than 10.") +elseif some_var < 10 # This elseif clause is optional. + println("some_var is smaller than 10.") +else # The else clause is optional too. + println("some_var is indeed 10.") +end + + +# For loops iterate over iterables, such as ranges, lists, sets, dicts, strings. + +for animal=["dog", "cat", "mouse"] + # You can use $ to interpolate into strings + println("$animal is a mammal") +end +# prints: +# dog is a mammal +# cat is a mammal +# mouse is a mammal + +# You can use in instead of =, if you want. +for animal in ["dog", "cat", "mouse"] + println("$animal is a mammal") +end + +for a in ["dog"=>"mammal","cat"=>"mammal","mouse"=>"mammal"] + println("$(a[1]) is $(a[2])") +end + +for (k,v) in ["dog"=>"mammal","cat"=>"mammal","mouse"=>"mammal"] + println("$k is $v") +end + + +# While loops go until a condition is no longer met. +# prints: +# 0 +# 1 +# 2 +# 3 +x = 0 +while x < 4 + println(x) + x += 1 # Shorthand for x = x + 1 +end + +# Handle exceptions with a try/except block +try + error("help") +catch e + println("caught it $e") +end +#=> caught it ErrorException("help") + + +#################################################### +## 4. Functions +#################################################### + +# Use the keyword function to create new functions +function add(x, y) + println("x is $x and y is $y") + + # Functions implicitly return the value of their last statement + x + y +end + +add(5, 6) #=> 11 after printing out "x is 5 and y is 6" + +# You can define functions that take a variable number of +# positional arguments +function varargs(args...) + return args +end + +varargs(1,2,3) #=> (1,2,3) + +# The ... is called a splat. +# It can also be used in a fuction call +# to splat a list or tuple out to be the arguments +Set([1,2,3]) #=> Set{Array{Int64,1}}([1,2,3]) # produces a Set of Arrays +Set([1,2,3]...) #=> Set{Int64}(1,2,3) # this is equivalent to Set(1,2,3) + +x = (1,2,3) #=> (1,2,3) +Set(x) #=> Set{(Int64,Int64,Int64)}((1,2,3)) # a Set of Tuples +Set(x...) #=> Set{Int64}(2,3,1) + + +# You can define functions with optional positional arguments +function defaults(a,b,x=5,y=6) + return "$a $b and $x $y" +end + +defaults('h','g') #=> "h g and 5 6" +defaults('h','g','j') #=> "h g and j 6" +defaults('h','g','j','k') #=> "h g and j k" +try + defaults('h') #=> ERROR: no method defaults(Char,) + defaults() #=> ERROR: no methods defaults() +catch e +println(e) +end + +# You can define functions that take keyword arguments +function keyword_args(;k1=4,name2="hello") # note the ; + return ["k1"=>k1,"name2"=>name2] +end + +keyword_args(name2="ness") #=> ["name2"=>"ness","k1"=>4] +keyword_args(k1="mine") #=> ["k1"=>"mine","name2"=>"hello"] +keyword_args() #=> ["name2"=>"hello","k2"=>4] + +# You can also do both at once +function all_the_args(normal_arg, optional_positional_arg=2; keyword_arg="foo") + println("normal arg: $normal_arg") + println("optional arg: $optional_positional_arg") + println("keyword arg: $keyword_arg") +end + +all_the_args(1, 3, keyword_arg=4) +# prints: +# normal arg: 1 +# optional arg: 3 +# keyword arg: 4 + +# Julia has first class functions +function create_adder(x) + adder = function (y) + return x + y + end + return adder +end + +# or equivalently +function create_adder(x) + y -> x + y +end + +# you can also name the internal function, if you want +function create_adder(x) + function adder(y) + x + y + end + adder +end + +add_10 = create_adder(10) +add_10(3) #=> 13 + +# The first two inner functions above are anonymous functions +(x -> x > 2)(3) #=> true + +# There are built-in higher order functions +map(add_10, [1,2,3]) #=> [11, 12, 13] +filter(x -> x > 5, [3, 4, 5, 6, 7]) #=> [6, 7] + +# We can use list comprehensions for nice maps and filters +[add_10(i) for i=[1, 2, 3]] #=> [11, 12, 13] +[add_10(i) for i in [1, 2, 3]] #=> [11, 12, 13] + +#################################################### +## 5. Types and Multiple-Dispatch +#################################################### + +# Type definition +type Tiger + taillength::Float64 + coatcolor # no type annotation is implicitly Any +end +# default constructor is the properties in order +# so, Tiger(taillength,coatcolor) + +# Type instantiation +tigger = Tiger(3.5,"orange") # the type doubles as the constructor function + +# Abtract Types +abstract Cat # just a name and point in the type hierarchy + +# * types defined with the type keyword are concrete types; they can be +# instantiated +# +# * types defined with the abstract keyword are abstract types; they can +# have subtypes. +# +# * each type has one supertype; a supertype can have zero or more subtypes. + +type Lion <: Cat # Lion is a subtype of Cat + mane_color + roar::String +end + +type Panther <: Cat # Panther is also a subtype of Cat + eye_color + Panther() = new("green") + # Panthers will only have this constructor, and no default constructor. +end + +# Multiple Dispatch + +# In Julia, all named functions are generic functions +# This means that they are built up from many small methods +# For example, let's make a function meow: +function meow(cat::Lion) + cat.roar # access properties using dot notation +end + +function meow(cat::Panther) + "grrr" +end + +function meow(cat::Tiger) + "rawwwr" +end + +meow(tigger) #=> "rawwr" +meow(Lion("brown","ROAAR")) #=> "ROAAR" +meow(Panther()) #=> "grrr" + +function pet_cat(cat::Cat) + println("The cat says $(meow(cat))") +end + +try + pet_cat(tigger) #=> ERROR: no method pet_cat(Tiger,) +catch e + println(e) +end + +pet_cat(Lion(Panther(),"42")) #=> prints "The cat says 42" + +``` + +## Further Reading + +You can get a lot more detail from [The Julia Manual](http://docs.julialang.org/en/latest/manual/) + diff --git a/lua.html.markdown b/lua.html.markdown index 66ebf6bd..4df57a92 100644 --- a/lua.html.markdown +++ b/lua.html.markdown @@ -2,6 +2,7 @@ language: lua author: Tyler Neylon author_url: http://tylerneylon.com/ +filename: learnlua.lua --- ```lua diff --git a/pets.csv b/pets.csv new file mode 100644 index 00000000..0837f473 --- /dev/null +++ b/pets.csv @@ -0,0 +1,4 @@ +name,age,weight,species +"fluffy",3,14,"cat" +"vesuvius",6,23,"fish" +"rex",5,34,"dog" diff --git a/php.html.markdown b/php.html.markdown index 753f6ab1..f0c5c918 100644 --- a/php.html.markdown +++ b/php.html.markdown @@ -2,19 +2,16 @@ language: php author: Malcolm Fell author_url: http://emarref.net/ +filename: learnphp.php --- This document describes PHP 5+. -## [Basic Syntax](http://www.php.net/manual/en/language.basic-syntax.php) - -All statements must end with a semi-colon; All PHP code must be between <?php and ?> tags. PHP can also be -configured to respect the [short open tags](http://www.php.net/manual/en/ini.core.php#ini.short-open-tag) <? and ?>. - -## [Comments](http://www.php.net/manual/en/language.basic-syntax.comments.php) - ```php -<?php +<?php // PHP code must be enclosed with <?php ? > tags + +// If your php file only contains PHP code, it is best practise +// to omit the php closing tag. // Two forward slashes start a one-line comment. @@ -24,27 +21,36 @@ configured to respect the [short open tags](http://www.php.net/manual/en/ini.cor Surrounding text in slash-asterisk and asterisk-slash makes it a multi-line comment. */ -``` - -## [Types](http://www.php.net/manual/en/language.types.php) -Types are [weakly typed](http://en.wikipedia.org/wiki/Strong_and_weak_typing) and begin with the $ symbol. -A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. +// Use "echo" or "print" to print output +print('Hello '); // Prints "Hello " with no line break -### Scalars +// () are optional for print and echo +echo "World\n"; // Prints "World" with a line break +// (all statements must end with a semicolon) -```php +// Anything outside <?php tags is echoed automatically +?>Hello World Again! <?php + +/************************************ + * Types & Variables + */ + +// Variables begin with the $ symbol. +// A valid variable name starts with a letter or underscore, +// followed by any number of letters, numbers, or underscores. + // Boolean values are case-insensitive -$boolean = true; // or TRUE or True +$boolean = true; // or TRUE or True $boolean = false; // or FALSE or False // Integers -$integer = 1234; // decimal number -$integer = -123; // a negative number -$integer = 0123; // octal number (equivalent to 83 decimal) -$integer = 0x1A; // hexadecimal number (equivalent to 26 decimal) +$int1 = 19; // => 19 +$int2 = -19; // => -19 +$int3 = 019; // => 15 (a leading 0 denotes an octal number) +$int4 = 0x0F; // => 15 (a leading 0x denotes a hex literal) // Floats (aka doubles) $float = 1.234; @@ -52,28 +58,30 @@ $float = 1.2e3; $float = 7E-10; // Arithmetic -$sum = $number + $float; -$difference = $number - $float; -$product = $number * $float; -$quotient = $number / $float; +$sum = 1 + 1; // 2 +$difference = 2 - 1; // 1 +$product = 2 * 2; // 4 +$quotient = 2 / 1; // 2 // Shorthand arithmetic -$number += 1; // Add 1 to $number -$number++; // Add 1 to $number after it is used -++$number; // Add 1 to $number before it is used. -$number /= $float // Divide and assign the quotient to $number +$number = 0; +$number += 1; // Increment $number by 1 +echo $number++; // Prints 1 (increments after evaluation) +echo ++$number; // Prints 3 (increments before evalutation) +$number /= $float; // Divide and assign the quotient to $number // Strings should be enclosed in single quotes; $sgl_quotes = '$String'; // => '$String' // Avoid using double quotes except to embed other variables -$dbl_quotes = "This is a $sgl_quotes." // => 'This is a $String' +$dbl_quotes = "This is a $sgl_quotes."; // => 'This is a $String.' -// Escape special characters with backslash -$escaped = "This contains a \t tab character."; +// Special characters are only escaped in double quotes +$escaped = "This contains a \t tab character."; +$unescaped = 'This just contains a slash and a t: \t'; // Enclose a variable in curly braces if needed -$money = "I have $${integer} in the bank." +$money = "I have $${number} in the bank."; // Since PHP 5.3, nowdocs can be used for uninterpolated multi-liners $nowdoc = <<<'END' @@ -81,35 +89,40 @@ Multi line string END; +// Heredocs will do string interpolation $heredoc = <<<END Multi line $sgl_quotes -END; // Nowdoc syntax is available in PHP 5.3.0 +END; -// Manipulation -$concatenated = $sgl_quotes . $dbl_quotes; -``` +// String concatenation is done with . +echo 'This string ' . 'is concatenated'; -### Compound -```php -<?php +/******************************** + * Arrays + */ -// Arrays -$array = array(1, 2, 3); -$array = [1, 2, 3]; // As of PHP 5.4 -$string = ["One", "Two", "Three"]; -$string[0]; // Holds the value "One"; +// All arrays in PHP are associative arrays (hashmaps), // Associative arrays, known as hashmaps in some languages. -$associative = ["One" => 1, "Two" => 2, "Three" => 3]; -$associative["One"]; // Holds the value 1 -``` -## Output +// Works with all PHP versions +$associative = array('One' => 1, 'Two' => 2, 'Three' => 3); -```php -<?php +// PHP 5.4 introduced a new syntax +$associative = ['One' => 1, 'Two' => 2, 'Three' => 3]; + +echo $associative['One']; // prints 1 + +// List literals implicitly assign integer keys +$array = ['One', 'Two', 'Three']; +echo $array[0]; // => "One" + + +/******************************** + * Output + */ echo('Hello World!'); // Prints Hello World! to stdout. @@ -121,133 +134,134 @@ print('Hello World!'); // The same as echo echo 'Hello World!'; print 'Hello World!'; // So is print -echo 100; -echo $variable; -echo function_result(); +$paragraph = 'paragraph'; + +echo 100; // Echo scalar variables directly +echo $paragraph; // or variables // If short open tags are configured, or your PHP version is // 5.4.0 or greater, you can use the short echo syntax -<?= $variable ?> -``` - -## [Operators](http://www.php.net/manual/en/language.operators.php) - -### Assignment - -```php +?> +<p><?= $paragraph ?></p> <?php $x = 1; $y = 2; -$x = $y; // A now contains the same value sa $y -$x = &$y; -// $x now contains a reference to $y. Changing the value of -// $x will change the value of $y also, and vice-versa. -``` +$x = $y; // $x now contains the same value as $y +$z = &$y; +// $z now contains a reference to $y. Changing the value of +// $z will change the value of $y also, and vice-versa. +// $x will remain unchanged as the original value of $y -### Comparison +echo $x; // => 2 +echo $z; // => 2 +$y = 0; +echo $x; // => 2 +echo $z; // => 0 -```php -<?php -// These comparisons will always be true, even if the types aren't the same. -$a == $b // TRUE if $a is equal to $b after type juggling. -$a != $b // TRUE if $a is not equal to $b after type juggling. -$a <> $b // TRUE if $a is not equal to $b after type juggling. -$a < $b // TRUE if $a is strictly less than $b. -$a > $b // TRUE if $a is strictly greater than $b. -$a <= $b // TRUE if $a is less than or equal to $b. -$a >= $b // TRUE if $a is greater than or equal to $b. +/******************************** + * Logic + */ +$a = 0; +$b = '0'; +$c = '1'; +$d = '1'; -// The following will only be true if the values match and are the same type. -$a === $b // TRUE if $a is equal to $b, and they are of the same type. -$a !== $b // TRUE if $a is not equal to $b, or they are not of the same type. -1 == '1' // TRUE -1 === '1' // FALSE -``` +// assert throws a warning if its argument is not true -## [Type Juggling](http://www.php.net/manual/en/language.types.type-juggling.php) +// These comparisons will always be true, even if the types aren't the same. +assert($a == $b); // equality +assert($c != $a); // inequality +assert($c <> $a); // alternative inequality +assert($a < $c); +assert($c > $b); +assert($a <= $b); +assert($c >= $d); -Variables can be converted between types, depending on their usage. +// The following will only be true if the values match and are the same type. +assert($c === $d); +assert($a !== $d); +assert(1 == '1'); +assert(1 !== '1'); -```php -<?php +// Variables can be converted between types, depending on their usage. $integer = 1; -echo $integer + $integer; // Outputs 2; +echo $integer + $integer; // => 2 $string = '1'; -echo $string + $string; -// Also outputs 2 because the + operator converts the strings to integers +echo $string + $string; // => 2 (strings are coerced to integers) $string = 'one'; -echo $string + $string; +echo $string + $string; // => 0 // Outputs 0 because the + operator cannot cast the string 'one' to a number -``` -Type casting can be used to treat a variable as another type temporarily by using cast operators in parentheses. +// Type casting can be used to treat a variable as another type -```php -$boolean = (boolean) $integer; // $boolean is true +$boolean = (boolean) 1; // => true $zero = 0; -$boolean = (boolean) $zero; // $boolean is false +$boolean = (boolean) $zero; // => false +// There are also dedicated functions for casting most types $integer = 5; $string = strval($integer); -// There are also dedicated functions for casting most types $var = null; // Null value -``` - -## [Control Structures](http://www.php.net/manual/en/language.control-structures.php) -### If Statements -```php -<?php +/******************************** + * Control Structures + */ -if (/* test */) { - // Do something +if (true) { + print 'I get printed'; } -if (/* test */) { - // Do something +if (false) { + print 'I don\'t'; } else { - // Do something else + print 'I get printed'; } -if (/* test */) { - // Do something -} elseif(/* test2 */) { - // Do something else, only if test2 +if (false) { + print 'Does not get printed'; +} elseif(true) { + print 'Does'; } -if (/* test */) { - // Do something -} elseif(/* test2 */) { - // Do something else, only if test2 +// ternary operator +print (false ? 'Does not get printed' : 'Does'); + +$x = 0; +if ($x === '0') { + print 'Does not print'; +} elseif($x == '1') { + print 'Does not print'; } else { - // Do something default + print 'Does print'; } + + + +// This alternative syntax is useful for templates: ?> -<?php if (/* test */): ?> +<?php if ($x): ?> This is displayed if the test is truthy. <?php else: ?> This is displayed otherwise. <?php endif; ?> -``` - -### Switch statements -```php <?php -switch ($variable) { - case 'one': - // Do something if $variable == 'one' - break; +// Use switch to save some logic. +switch ($x) { + case '0': + print 'Switch does type coercion'; + break; // You must include a break, or you will fall through + // to cases 'two' and 'three' case 'two': case 'three': // Do something if $variable is either 'two' or 'three' @@ -256,199 +270,231 @@ switch ($variable) { // Do something by default } -``` - -### Loops - -```php -<?php - +// While, do...while and for loops are probably familiar $i = 0; while ($i < 5) { echo $i++; -} +}; // Prints "01234" + +echo "\n"; $i = 0; do { echo $i++; -} while ($i < 5); +} while ($i < 5); // Prints "01234" + +echo "\n"; for ($x = 0; $x < 10; $x++) { - echo $x; // Will echo 0 - 9 -} + echo $x; +} // Prints "0123456789" + +echo "\n"; + +$wheels = ['bicycle' => 2, 'car' => 4]; -$wheels = ["bicycle" => 2, "car" => 4]; +// Foreach loops can iterate over arrays +foreach ($wheels as $wheel_count) { + echo $wheel_count; +} // Prints "24" +echo "\n"; + +// You can iterate over the keys as well as the values foreach ($wheels as $vehicle => $wheel_count) { echo "A $vehicle has $wheel_count wheels"; } -// This loop will stop after outputting 2 +echo "\n"; + $i = 0; while ($i < 5) { - if ($i == 3) { - break; // Exit out of the while loop and continue. + if ($i === 3) { + break; // Exit out of the while loop } echo $i++; -} +} // Prints "012" -// This loop will output everything except 3 -$i = 0; -while ($i < 5) { - if ($i == 3) { +for ($i = 0; $i < 5; $i++) { + if ($i === 3) { continue; // Skip this iteration of the loop } - echo $i++; -} -``` - -## Functions + echo $i; +} // Prints "0124" -Functions are created with the ```function``` keyword. -```php -<?php +/******************************** + * Functions + */ -function my_function($my_arg) { - $my_variable = 1; +// Define a function with "function": +function my_function () { + return 'Hello'; } -// $my_variable and $my_arg cannot be accessed outside of the function -``` - -Functions may be invoked by name. - -```php -<?php +echo my_function(); // => "Hello" -my_function_name(); +// A valid function name starts with a letter or underscore, followed by any +// number of letters, numbers, or underscores. -$variable = get_something(); // A function may return a value -``` - -A valid function name starts with a letter or underscore, followed by any -number of letters, numbers, or underscores. There are three ways to declare functions. - -### [User-defined](http://www.php.net/manual/en/functions.user-defined.php) - -```php -<?php - -function my_function_name ($arg_1, $arg_2) { - // $arg_1 and $arg_2 are required +function add ($x, $y = 1) { // $y is optional and defaults to 1 + $result = $x + $y; + return $result; } -// Functions may be nested to limit scope -function outer_function ($arg_1 = null) { // $arg_1 is optional - function inner_function($arg_2 = 'two') { // $arg_2 will default to 'two' - } -} +echo add(4); // => 5 +echo add(4, 2); // => 6 -// inner_function() does not exist and cannot be called until -// outer_function() is called -``` +// $result is not accessible outside the function +// print $result; // Gives a warning. -This enables [currying](http://en.wikipedia.org/wiki/Currying) in PHP. +// Since PHP 5.3 you can declare anonymous functions; +$inc = function ($x) { + return $x + 1; +}; + +echo $inc(2); // => 3 -```php function foo ($x, $y, $z) { echo "$x - $y - $z"; } +// Functions can return functions function bar ($x, $y) { + // Use 'use' to bring in outside variables return function ($z) use ($x, $y) { foo($x, $y, $z); }; } $bar = bar('A', 'B'); -$bar('C'); -``` - -### [Variable](http://www.php.net/manual/en/functions.variable-functions.php) +$bar('C'); // Prints "A - B - C" -```php -<?php +// You can call named functions using strings +$function_name = 'add'; +echo $function_name(1, 2); // => 3 +// Useful for programatically determining which function to run. +// Or, use call_user_func(callable $callback [, $parameter [, ... ]]); -$function_name = 'my_function_name'; +/******************************** + * Includes + */ -$function_name(); // will execute the my_function_name() function +/* ``` - -### [Anonymous](http://www.php.net/manual/en/functions.anonymous.php) - -Similar to variable functions, functions may be anonymous. - ```php <?php +// PHP within included files must also begin with a PHP open tag. -function my_function($callback) { - $callback('My argument'); -} +include 'my-file.php'; +// The code in my-file.php is now available in the current scope. +// If the file cannot be included (e.g. file not found), a warning is emitted. -my_function(function ($my_argument) { - // do something -}); +include_once 'my-file.php'; +// If the code in my-file.php has been included elsewhere, it will +// not be included again. This prevents multiple class declaration errors -// Closure style -$my_function = function() { - // Do something -}; +require 'my-file.php'; +require_once 'my-file.php'; +// Same as include(), except require() will cause a fatal error if the +// file cannot be included. -$my_function(); -``` +// Contents of my-include.php: +<?php -## [Classes](http://www.php.net/manual/en/language.oop5.php) +return 'Anything you like.'; +// End file -Classes are defined with the ```class``` keyword. +// Includes and requires may also return a value. +$value = include 'my-include.php'; -```php -<?php +// Files are included based on the file path given or, if none is given, +// the include_path configuration directive. If the file isn't found in +// the include_path, include will finally check in the calling script's +// own directory and the current working directory before failing. +/* */ -class MyClass { - const MY_CONST = 'value'; - static $staticVar = 'something'; - public $property = 'value'; // Properties must declare their visibility -} +/******************************** + * Classes + */ -echo MyClass::MY_CONST; // Outputs "value"; +// Classes are defined with the class keyword -final class YouCannotExtendMe { -} -``` +class MyClass +{ + const MY_CONST = 'value'; // A constant -Classes are insantiated with the ```new``` keyword. Functions are referred to as -methods if they belong to a class. + static $staticVar = 'static'; -```php -<?php + // Properties must declare their visibility + public $property = 'public'; + public $instanceProp; + protected $prot = 'protected'; // Accessible from the class and subclasses + private $priv = 'private'; // Accessible within the class only -class MyClass { - function myFunction() { + // Create a constructor with __construct + public function __construct($instanceProp) { + // Access instance variables with $this + $this->instanceProp = $instanceProp; } - final function youCannotOverrideMe() { + // Methods are declared as functions inside a class + public function myMethod() + { + print 'MyClass'; } - public static function myStaticMethod() { + final function youCannotOverrideMe() + { + } + + public static function myStaticMethod() + { + print 'I am static'; } } -$cls = new MyClass(); // The parentheses are optional. +echo MyClass::MY_CONST; // Outputs 'value'; +echo MyClass::$staticVar; // Outputs 'static'; +MyClass::myStaticMethod(); // Outputs 'I am static'; -echo MyClass::$staticVar; // Access to static vars +// Instantiate classes using new +$my_class = new MyClass('An instance property'); +// The parentheses are optional if not passing in an argument. -echo $cls->property; // Access to properties +// Access class members using -> +echo $my_class->property; // => "public" +echo $my_class->instanceProp; // => "An instance property" +$my_class->myMethod(); // => "MyClass" -MyClass::myStaticMethod(); // myStaticMethod cannot be run on $cls -``` -PHP offers some [magic methods](http://www.php.net/manual/en/language.oop5.magic.php) for classes. +// Extend classes using "extends" +class MyOtherClass extends MyClass +{ + function printProtectedProperty() + { + echo $this->prot; + } -```php -<?php + // Override a method + function myMethod() + { + parent::myMethod(); + print ' > MyOtherClass'; + } +} -class MyClass { +$my_other_class = new MyOtherClass('Instance prop'); +$my_other_class->printProtectedProperty(); // => Prints "protected" +$my_other_class->myMethod(); // Prints "MyClass > MyOtherClass" + +final class YouCannotExtendMe +{ +} + +// You can use "magic methods" to create getters and setters +class MyMapClass +{ private $property; public function __get($key) @@ -462,16 +508,13 @@ class MyClass { } } -$x = new MyClass(); +$x = new MyMapClass(); echo $x->property; // Will use the __get() method $x->property = 'Something'; // Will use the __set() method -``` -Classes can be abstract (using the ```abstract``` keyword), extend other classes (using the ```extends``` keyword) and -implement interfaces (using the ```implements``` keyword). An interface is declared with the ```interface``` keyword. - -```php -<?php +// Classes can be abstract (using the abstract keyword) or +// implement interfaces (using the implements keyword). +// An interface is declared with the interface keyword. interface InterfaceOne { @@ -480,90 +523,112 @@ interface InterfaceOne interface InterfaceTwo { - public function doSomething(); + public function doSomethingElse(); } abstract class MyAbstractClass implements InterfaceOne { + public $x = 'doSomething'; } -class MyClass extends MyAbstractClass implements InterfaceTwo +class MyConcreteClass extends MyAbstractClass implements InterfaceTwo { + public function doSomething() + { + echo $x; + } + + public function doSomethingElse() + { + echo 'doSomethingElse'; + } } + // Classes can implement more than one interface class SomeOtherClass implements InterfaceOne, InterfaceTwo { + public function doSomething() + { + echo 'doSomething'; + } + + public function doSomethingElse() + { + echo 'doSomethingElse'; + } } -``` -### [Namespaces](http://www.php.net/manual/en/language.namespaces.rationale.php) -By default, classes exist in the global namespace, and can be explicitly called with a backslash. +/******************************** + * Traits + */ + +// Traits are available from PHP 5.4.0 and are declared using "trait" + +trait MyTrait +{ + public function myTraitMethod() + { + print 'I have MyTrait'; + } +} + +class MyTraitfulClass +{ + use MyTrait; +} + +$cls = new MyTraitfulClass(); +$cls->myTraitMethod(); // Prints "I have MyTrait" + +/******************************** + * Namespaces + */ + +// This section is separate, because a namespace declaration +// must be the first statement in a file. Let's pretend that is not the case + +/* +``` ```php <?php +// By default, classes exist in the global namespace, and can +// be explicitly called with a backslash. + $cls = new \MyClass(); -``` -```php -<?php + +// Set the namespace for a file namespace My\Namespace; class MyClass { } +// (from another file) $cls = new My\Namespace\MyClass; -``` - -Or from within another namespace. - -```php -<?php +//Or from within another namespace. namespace My\Other\Namespace; use My\Namespace\MyClass; $cls = new MyClass(); -``` -Or you can alias the namespace; - -```php -<?php +// Or you can alias the namespace; namespace My\Other\Namespace; use My\Namespace as SomeOtherNamespace; $cls = new SomeOtherNamespace\MyClass(); -``` - -### [Traits](http://www.php.net/manual/en/language.oop5.traits.php) - -Traits are available since PHP 5.4.0 and are declared using the ```trait``` keyword. - -```php -<?php -trait MyTrait { - public function myTraitMethod() - { - // Do something - } -} - -class MyClass -{ - use MyTrait; -} +*/ -$cls = new MyClass(); -$cls->myTraitMethod(); ``` ## More Information @@ -573,3 +638,5 @@ Visit the [official PHP documentation](http://www.php.net/manual/) for reference If you're interested in up-to-date best practices, visit [PHP The Right Way](http://www.phptherightway.com/). If you're coming from a language with good package management, check out [Composer](http://getcomposer.org/). + +For common standards, visit the PHP Framework Interoperability Group's [PSR standards](https://github.com/php-fig/fig-standards). diff --git a/python.html.markdown b/python.html.markdown index 982333ca..e0851950 100644 --- a/python.html.markdown +++ b/python.html.markdown @@ -2,19 +2,23 @@ language: python author: Louie Dinh author_url: http://ldinh.ca +filename: learnpython.py --- Python was created by Guido Van Rossum in the early 90's. It is now one of the most popular languages in existence. I fell in love with Python for it's syntactic clarity. It's basically executable pseudocode. +Feedback would be highly appreciated! You can reach me at [@louiedinh](http://twitter.com/louiedinh) or louiedinh [at] [google's email service] + Note: This article applies to Python 2.7 specifically, but should be applicable to Python 2.x. Look for another tour of Python 3 soon! ```python # Single line comments start with a hash. -""" Multiline comments can we written - using three "'s +""" Multiline strings can be written + using three "'s, and are often used + as comments """ #################################################### @@ -32,11 +36,11 @@ to Python 2.x. Look for another tour of Python 3 soon! # Division is a bit tricky. It is integer division and floors the results # automatically. -11 / 4 #=> 2 +5 / 2 #=> 2 # To fix division we need to learn about floats. 2.0 # This is a float -5.0 / 2.0 #=> 2.5 ahhh...much better +11.0 / 4.0 #=> 2.75 ahhh...much better # Enforce precedence with parentheses (1 + 3) * 2 #=> 8 @@ -77,9 +81,32 @@ not False #=> True # A string can be treated like a list of characters "This is a string"[0] #=> 'T' +# % can be used to format strings, like this: +"%s can be %s" % ("strings", "interpolated") + +# A newer way to format strings is the format method. +# This method is the preferred way +"{0} can be {1}".format("strings", "formatted") +# You can use keywords if you don't want to count. +"{name} wants to eat {food}".format(name="Bob", food="lasagna") + # None is an object None #=> None +# Don't use the equality `==` symbol to compare objects to None +# Use `is` instead +"etc" is None #=> False +None is None #=> True + +# The 'is' operator tests for object identity. This isn't +# very useful when dealing with primitive values, but is +# very useful when dealing with objects. + +# None, 0, and empty strings/lists all evaluate to False. +# All other values are True +0 == False #=> True +"" == False #=> True + #################################################### ## 2. Variables and Collections @@ -93,16 +120,12 @@ print "I'm Python. Nice to meet you!" some_var = 5 # Convention is to use lower_case_with_underscores some_var #=> 5 -# Accessing a previously unassigned variable is an exception -try: - some_other_var -except NameError: - print "Raises a name error" +# Accessing a previously unassigned variable is an exception. +# See Control Flow to learn more about exception handling. +some_other_var # Raises a name error -# Conditional Expressions can be used when assigning -some_var = a if a > b else b -# If a is greater than b, then a is assigned to some_var. -# Otherwise b is assigned to some_var. +# if can be used as an expression +"yahoo!" if 3 > 2 else 2 #=> "yahoo!" # Lists store sequences li = [] @@ -122,21 +145,18 @@ li.append(3) # li is now [1, 2, 4, 3] again. # Access a list like you would any array li[0] #=> 1 # Look at the last element -li[-1] #=> 4 +li[-1] #=> 3 # Looking out of bounds is an IndexError -try: - li[4] # Raises an IndexError -except IndexError: - print "Raises an IndexError" +li[4] # Raises an IndexError # You can look at ranges with slice syntax. # (It's a closed/open range for you mathy types.) li[1:3] #=> [2, 4] # Omit the beginning -li[:3] #=> [1, 2, 4] -# Omit the end li[2:] #=> [4, 3] +# Omit the end +li[:3] #=> [1, 2, 4] # Remove arbitrary elements from a list with del del li[2] # li is now [1, 2, 3] @@ -145,7 +165,7 @@ del li[2] # li is now [1, 2, 3] li + other_li #=> [1, 2, 3, 4, 5, 6] - Note: li and other_li is left alone # Concatenate lists with extend -li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6] +li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6] # Check for existence in a list with in 1 in li #=> True @@ -153,13 +173,11 @@ li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6] # Examine the length with len len(li) #=> 6 + # Tuples are like lists but are immutable. tup = (1, 2, 3) tup[0] #=> 1 -try: - tup[0] = 3 # Raises a TypeError -except TypeError: - print "Tuples cannot be mutated." +tup[0] = 3 # Raises a TypeError # You can do all those list thingies on tuples too len(tup) #=> 3 @@ -167,7 +185,7 @@ tup + (4, 5, 6) #=> (1, 2, 3, 4, 5, 6) tup[:2] #=> (1, 2) 2 in tup #=> True -# However, you can unpack tuples into variables +# You can unpack tuples (or lists) into variables a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3 # Tuples are created by default if you leave out the parentheses d, e, f = 4, 5, 6 @@ -196,10 +214,13 @@ filled_dict.values() #=> [3, 2, 1] "one" in filled_dict #=> True 1 in filled_dict #=> False -# Trying to look up a non-existing key will raise a KeyError -filled_dict["four"] #=> KeyError + # Looking up a non-existing key is a KeyError +filled_dict["four"] # KeyError # Use get method to avoid the KeyError +filled_dict.get("one") #=> 1 +filled_dict.get("four") #=> None +# The get method supports a default argument when the value is missing filled_dict.get("one", 4) #=> 1 filled_dict.get("four", 4) #=> 4 @@ -211,18 +232,23 @@ filled_dict.setdefault("five", 6) #filled_dict["five"] is still 5 # Sets store ... well sets empty_set = set() # Initialize a set with a bunch of values -filled_set = set([1,2,2,3,4]) # filled_set is now set([1, 2, 3, 4]) +some_set = set([1,2,2,3,4]) # filled_set is now set([1, 2, 3, 4]) + +# Since Python 2.7, {} can be used to declare a set +filled_set = {1, 2, 2, 3, 4} # => {1 2 3 4} # Add more items to a set -filled_set.add(5) # filled_set is now set([1, 2, 3, 4, 5]) +filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5} # Do set intersection with & -other_set = set([3, 4, 5 ,6]) -filled_set & other_set #=> set([3, 4, 5]) +other_set = {3, 4, 5, 6} +filled_set & other_set #=> {3, 4, 5} + # Do set union with | -filled_set | other_set #=> set([1, 2, 3, 4, 5, 6]) +filled_set | other_set #=> {1, 2, 3, 4, 5, 6} + # Do set difference with - -set([1,2,3,4]) - set([2,3,5]) #=> set([1, 4]) +{1,2,3,4} - {2,3,5} #=> {1, 4} # Check for existence in a set with in 2 in filled_set #=> True @@ -236,7 +262,7 @@ set([1,2,3,4]) - set([2,3,5]) #=> set([1, 4]) # Let's just make a variable some_var = 5 -# Here is an if statement. INDENTATION IS SIGNIFICANT IN PYTHON! +# Here is an if statement. Indentation is significant in python! # prints "some var is smaller than 10" if some_var > 10: print "some_var is totally bigger than 10." @@ -255,14 +281,26 @@ prints: """ for animal in ["dog", "cat", "mouse"]: # You can use % to interpolate formatted strings - print "%s is a mammal" % animal + print "%s is a mammal" % animal + +""" +`range(number)` returns a list of numbers +from zero to the given number +prints: + 0 + 1 + 2 + 3 +""" +for i in range(4): + print i """ While loops go until a condition is no longer met. prints: 0 1 - 2 + 2 3 """ x = 0 @@ -279,12 +317,6 @@ try: except IndexError as e: pass # Pass is just a no-op. Usually you would do recovery here. -# Works for Python 2.7 and down: -try: - raise IndexError("This is an index error") -except IndexError, e: # No "as", comma instead - pass - #################################################### ## 4. Functions @@ -296,7 +328,8 @@ def add(x, y): return x + y # Return values with a return statement # Calling functions with parameters -add(5, 6) #=> 11 and prints out "x is 5 and y is 6" +add(5, 6) #=> prints out "x is 5 and y is 6" and returns 11 + # Another way to call functions is with keyword arguments add(y=6, x=5) # Keyword arguments can arrive in any order. @@ -322,16 +355,17 @@ def all_the_args(*args, **kwargs): print kwargs """ all_the_args(1, 2, a=3, b=4) prints: - [1, 2] + (1, 2) {"a": 3, "b": 4} """ -# You can also use * and ** when calling a function +# When calling functions, you can do the opposite of varargs/kwargs! +# Use * to expand tuples and use ** to expand kwargs. args = (1, 2, 3, 4) kwargs = {"a": 3, "b": 4} -foo(*args) # equivalent to foo(1, 2, 3, 4) -foo(**kwargs) # equivalent to foo(a=3, b=4) -foo(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4) +all_the_args(*args) # equivalent to foo(1, 2, 3, 4) +all_the_args(**kwargs) # equivalent to foo(a=3, b=4) +all_the_args(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4) # Python has first class functions def create_adder(x): @@ -395,11 +429,53 @@ print j.say("hello") #prints out "Joel: hello" i.get_species() #=> "H. sapiens" # Change the shared attribute -i.species = "H. neanderthalensis" +Human.species = "H. neanderthalensis" i.get_species() #=> "H. neanderthalensis" j.get_species() #=> "H. neanderthalensis" # Call the static method Human.grunt() #=> "*grunt*" + + +#################################################### +## 6. Modules +#################################################### + +# You can import modules +import math +print math.sqrt(16) #=> 4 + +# You can get specific functions from a module +from math import ceil, floor +print ceil(3.7) #=> 4.0 +print floor(3.7) #=> 3.0 + +# You can import all functions from a module. +# Warning: this is not recommended +from math import * + +# You can shorten module names +import math as m +math.sqrt(16) == m.sqrt(16) #=> True + +# Python modules are just ordinary python files. You +# can write your own, and import them. The name of the +# module is the same as the name of the file. + +# You can find out which functions and attributes +# defines a module. +import math +dir(math) + + ``` +## Further Reading + +Still up for more? Try: + +* [Learn Python The Hard Way](http://learnpythonthehardway.org/book/) +* [Dive Into Python](http://www.diveintopython.net/) +* [The Official Docs](http://docs.python.org/2.6/) +* [Hitchhiker's Guide to Python](http://docs.python-guide.org/en/latest/) +* [Python Module of the Week](http://pymotw.com/2/) diff --git a/r.html.markdown b/r.html.markdown new file mode 100644 index 00000000..535b9065 --- /dev/null +++ b/r.html.markdown @@ -0,0 +1,350 @@ +--- +language: R +author: e99n09 +author_url: http://github.com/e99n09 +filename: learnr.r +--- + +R is a statistical computing language. It has lots of good built-in functions for uploading and cleaning data sets, running common statistical tests, and making graphs. You can also easily compile it within a LaTeX document. + +```python + +# Comments start with hashtags. + +# You can't make a multi-line comment per se, +# but you can stack multiple comments like so. + +# Hit COMMAND-ENTER to execute a line + +######################### +# The absolute basics +######################### + +# NUMBERS + +# We've got doubles! Behold the "numeric" class +5 # => [1] 5 +class(5) # => [1] "numeric" +# We've also got integers! They look suspiciously similar, +# but indeed are different +5L # => [1] 5 +class(5L) # => [1] "integer" +# Try ?class for more information on the class() function +# In fact, you can look up the documentation on just about anything with ? + +# All the normal operations! +10 + 66 # => [1] 76 +53.2 - 4 # => [1] 49.2 +2 * 2.0 # => [1] 4 +3L / 4 # => [1] 0.75 +3 %% 2 # => [1] 1 + +# Finally, we've got not-a-numbers! They're numerics too +class(NaN) # => [1] "numeric" + +# CHARACTERS + +# We've (sort of) got strings! Behold the "character" class +"plugh" # => [1] "plugh" +class("plugh") # "character" +# There's no difference between strings and characters in R + +# LOGICALS + +# We've got booleans! Behold the "logical" class +class(TRUE) # => [1] "logical" +class(FALSE) # => [1] "logical" +# Behavior is normal +TRUE == TRUE # => [1] TRUE +TRUE == FALSE # => [1] FALSE +FALSE != FALSE # => [1] FALSE +FALSE != TRUE # => [1] TRUE +# Missing data (NA) is logical, too +class(NA) # => [1] "logical" + +# FACTORS + +# The factor class is for categorical data +# It has an attribute called levels that describes all the possible categories +factor("dog") +# => +# [1] dog +# Levels: dog +# (This will make more sense once we start talking about vectors) + +# VARIABLES + +# Lots of way to assign stuff +x = 5 # this is possible +y <- "1" # this is preferred +TRUE -> z # this works but is weird + +# We can use coerce variables to different classes +as.numeric(y) # => [1] 1 +as.character(x) # => [1] "5" + +# LOOPS + +# We've got for loops +for (i in 1:4) { + print(i) +} + +# We've got while loops +a <- 10 +while (a > 4) { + cat(a, "...", sep = "") + a <- a - 1 +} + +# Keep in mind that for and while loops run slowly in R +# Operations on entire vectors (i.e. a whole row, a whole column) +# or apply()-type functions (we'll discuss later) are preferred + +# IF/ELSE + +# Again, pretty standard +if (4 > 3) { + print("Huzzah! It worked!") +} else { + print("Noooo! This is blatantly illogical!") +} +# => +# [1] "Huzzah! It worked!" + +# FUNCTIONS + +# Defined like so: +myFunc <- function(x) { + x <- x * 4 + x <- x - 1 + return(x) +} + +# Called like any other R function: +myFunc(5) # => [1] 19 + +######################### +# Fun with data: vectors, matrices, data frames, and arrays +######################### + +# ONE-DIMENSIONAL + +# You can vectorize anything, so long as all components have the same type +vec <- c(8, 9, 10, 11) +vec # => [1] 8 9 10 11 +# The class of a vector is the class of its components +class(vec) # => [1] "numeric" +# If you vectorize items of different classes, weird coercions happen +c(TRUE, 4) # => [1] 1 4 +c("dog", TRUE, 4) # => [1] "dog" "TRUE" "4" + +# We ask for specific components like so (R starts counting from 1) +vec[1] # => [1] 8 +# We can also search for the indices of specific components, +which(vec %% 2 == 0) # => [1] 1 3 +# or grab just the first or last entry in the vector +head(vec, 1) # => [1] 8 +tail(vec, 1) # => [1] 11 +# If an index "goes over" you'll get NA: +vec[6] # => [1] NA +# You can find the length of your vector with length() +length(vec) # => [1] 4 + +# You can perform operations on entire vectors or subsets of vectors +vec * 4 # => [1] 16 20 24 28 +vec[2:3] * 5 # => [1] 25 30 +# and there are many built-in functions to summarize vectors +mean(vec) # => [1] 9.5 +var(vec) # => [1] 1.666667 +sd(vec) # => [1] 1.290994 +max(vec) # => [1] 11 +min(vec) # => [1] 8 +sum(vec) # => [1] 38 + +# TWO-DIMENSIONAL (ALL ONE CLASS) + +# You can make a matrix out of entries all of the same type like so: +mat <- matrix(nrow = 3, ncol = 2, c(1,2,3,4,5,6)) +mat +# => +# [,1] [,2] +# [1,] 1 4 +# [2,] 2 5 +# [3,] 3 6 +# Unlike a vector, the class of a matrix is "matrix", no matter what's in it +class(mat) # => "matrix" +# Ask for the first row +mat[1,] # => [1] 1 4 +# Perform operation on the first column +3 * mat[,1] # => [1] 3 6 9 +# Ask for a specific cell +mat[3,2] # => [1] 6 +# Transpose the whole matrix +t(mat) +# => +# [,1] [,2] [,3] +# [1,] 1 2 3 +# [2,] 4 5 6 + +# cbind() sticks vectors together column-wise to make a matrix +mat2 <- cbind(1:4, c("dog", "cat", "bird", "dog")) +mat2 +# => +# [,1] [,2] +# [1,] "1" "dog" +# [2,] "2" "cat" +# [3,] "3" "bird" +# [4,] "4" "dog" +class(mat2) # => [1] matrix +# Again, note what happened! +# Because matrices must contain entries all of the same class, +# everything got converted to the character class +c(class(mat2[,1]), class(mat2[,2])) + +# rbind() sticks vectors together row-wise to make a matrix +mat3 <- rbind(c(1,2,4,5), c(6,7,0,4)) +mat3 +# => +# [,1] [,2] [,3] [,4] +# [1,] 1 2 4 5 +# [2,] 6 7 0 4 +# Aah, everything of the same class. No coercions. Much better. + +# TWO-DIMENSIONAL (DIFFERENT CLASSES) + +# For columns of different classes, use the data frame +dat <- data.frame(c(5,2,1,4), c("dog", "cat", "bird", "dog")) +names(dat) <- c("number", "species") # name the columns +class(dat) # => [1] "data.frame" +dat +# => +# number species +# 1 5 dog +# 2 2 cat +# 3 1 bird +# 4 4 dog +class(dat$number) # => [1] "numeric" +class(dat[,2]) # => [1] "factor" +# The data.frame() function converts character vectors to factor vectors + +# There are many twisty ways to subset data frames, all subtly unalike +dat$number # => [1] 5 2 1 4 +dat[,1] # => [1] 5 2 1 4 +dat[,"number"] # => [1] 5 2 1 4 + +# MULTI-DIMENSIONAL (ALL OF ONE CLASS) + +# Arrays creates n-dimensional tables +# You can make a two-dimensional table (sort of like a matrix) +array(c(c(1,2,4,5),c(8,9,3,6)), dim=c(2,4)) +# => +# [,1] [,2] [,3] [,4] +# [1,] 1 4 8 3 +# [2,] 2 5 9 6 +# You can use array to make three-dimensional matrices too +array(c(c(c(2,300,4),c(8,9,0)),c(c(5,60,0),c(66,7,847))), dim=c(3,2,2)) +# => +# , , 1 +# +# [,1] [,2] +# [1,] 1 4 +# [2,] 2 5 +# +# , , 2 +# +# [,1] [,2] +# [1,] 8 1 +# [2,] 9 2 + +# LISTS (MULTI-DIMENSIONAL, POSSIBLY RAGGED, OF DIFFERENT TYPES) + +# Finally, R has lists (of vectors) +list1 <- list(time = 1:40) +list1$price = c(rnorm(40,.5*list1$time,4)) # random +list1 + +# You can get items in the list like so +list1$time +# You can subset list items like vectors +list1$price[4] + +######################### +# The apply() family of functions +######################### + +# Remember mat? +mat +# => +# [,1] [,2] +# [1,] 1 4 +# [2,] 2 5 +# [3,] 3 6 +# Use apply(X, MARGIN, FUN) to apply function FUN to a matrix X +# over rows (MAR = 1) or columns (MAR = 2) +# That is, R does FUN to each row (or column) of X, much faster than a +# for or while loop would do +apply(mat, MAR = 2, myFunc) +# => +# [,1] [,2] +# [1,] 3 15 +# [2,] 7 19 +# [3,] 11 23 +# Other functions: ?lapply, ?sapply + +# Don't feel too intimidated; everyone agrees they are rather confusing + +# The plyr package aims to replace (and improve upon!) the *apply() family. + +install.packages("plyr") +require(plyr) +?plyr + +######################### +# Loading data +######################### + +# "pets.csv" is a file on the internet +pets <- read.csv("http://learnxinyminutes.com/docs/pets.csv") +pets +head(pets, 2) # first two rows +tail(pets, 1) # last row + +# To save a data frame or matrix as a .csv file +write.csv(pets, "pets2.csv") # to make a new .csv file +# set working directory with setwd(), look it up with getwd() + +# Try ?read.csv and ?write.csv for more information + +######################### +# Plots +######################### + +# Scatterplots! +plot(list1$time, list1$price, main = "fake data") +# Regressions! +linearModel <- lm(price ~ time, data = list1) +linearModel # outputs result of regression +# Plot regression line on existing plot +abline(linearModel, col = "red") +# Get a variety of nice diagnostics +plot(linearModel) + +# Histograms! +hist(rpois(n = 10000, lambda = 5), col = "thistle") + +# Barplots! +barplot(c(1,4,5,1,2), names.arg = c("red","blue","purple","green","yellow")) + +# Try the ggplot2 package for more and better graphics + +install.packages("ggplot2") +require(ggplot2) +?ggplot2 + +``` + +## How do I get R? + +* Get R and the R GUI from [http://www.r-project.org/](http://www.r-project.org/) +* [RStudio](http://www.rstudio.com/ide/) is another GUI |