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| -rw-r--r-- | julia.html.markdown | 525 | ||||
| -rw-r--r-- | php.html.markdown | 5 | ||||
| -rw-r--r-- | python.html.markdown | 10 | ||||
| -rw-r--r-- | ruby.html.markdown | 306 |
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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 index 66370a7d..42d0b809 100644 --- a/erlang.html.markdown +++ b/erlang.html.markdown @@ -5,7 +5,7 @@ author_url: http://www.focustheweb.com/ filename: learnerlang.erl --- -```latex +```erlang % Percent sign start a one-line comment. %% Two percent characters shall be used to comment functions. 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/php.html.markdown b/php.html.markdown index 75bbd214..f0c5c918 100644 --- a/php.html.markdown +++ b/php.html.markdown @@ -231,6 +231,9 @@ if (false) { print 'Does'; } +// ternary operator +print (false ? 'Does not get printed' : 'Does'); + $x = 0; if ($x === '0') { print 'Does not print'; @@ -240,6 +243,8 @@ if ($x === '0') { print 'Does print'; } + + // This alternative syntax is useful for templates: ?> diff --git a/python.html.markdown b/python.html.markdown index 59a0b85c..fe8a204c 100644 --- a/python.html.markdown +++ b/python.html.markdown @@ -6,7 +6,7 @@ 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 +languages in existence. I fell in love with Python for its syntactic clarity. Its 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] @@ -328,7 +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. @@ -461,6 +462,11 @@ math.sqrt(16) == m.sqrt(16) #=> True # 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) + ``` diff --git a/ruby.html.markdown b/ruby.html.markdown new file mode 100644 index 00000000..2de134ae --- /dev/null +++ b/ruby.html.markdown @@ -0,0 +1,306 @@ +--- +language: ruby +contributors: + - ["David Underwood", "http://theflyingdeveloper.com"] +--- + +```ruby +# This is a comment + +=begin +This is a multiline comment +No-one uses them +You shouldn't either +=end + +# First and foremost: Everything is an object. + +# Numbers are objects + +3.class #=> Fixnum + +3.to_s #=> "3" + + +# Some basic arithmetic +1 + 1 #=> 2 +8 - 1 #=> 7 +10 * 2 #=> 20 +35 / 5 #=> 7 + +# Special values are objects +nil # Nothing to see here +true # truth +false # falsehood + +nil.class #=> NilClass +true.class #=> TrueClass +false.class #=> FalseClass + +# Equality +1 == 1 #=> true +2 == 1 #=> false + +# apart from false itself, nil is the only other 'falsey' value + +nil == false #=> true +0 == false #=> false + +# Inequality +1 != 1 #=> false +2 != 1 #=> true +!true #=> false +!false #=> true + +# More comparisons +1 < 10 #=> true +1 > 10 #=> false +2 <= 2 #=> true +2 >= 2 #=> true + +# Strings are objects + +'I am a string'.class #=> String +"I am a string too".class #=> String + +placeholder = "use string interpolation" +"I can #{placeholder} when using double quoted strings" +#=> "I can use string interpolation when using double quoted strings" + + +# print to the output +puts "I'm printing!" + +# Variables +x = 25 #=> 25 +x #=> 25 + +# Note that assignment returns the value assigned +# This means you can do multiple assignment: + +x = y = 10 #=> 10 +x #=> 10 +y #=> 10 + +# By convention, use snake_case for variable names +snake_case = true + +# Use descriptive variable names +path_to_project_root = '/good/name/' +path = '/bad/name/' + +# Symbols (are objects) +# Symbols are immutable, reusable constants represented internally by an integer value +# They're often used instead of strings to efficiently convey specific, meaningful values + +:pending.class #=> Symbol + +status = :pending + +status == :pending #=> true + +status == 'pending' #=> false + +status == :approved #=> false + +# Arrays + +# This is an array +[1, 2, 3, 4, 5] #=> [1, 2, 3, 4, 5] + +# Arrays can contain different types of items + +array = [1, "hello", false] #=> => [1, "hello", false] + +# Arrays can be indexed +# From the front +array[0] #=> 1 +array[12] #=> nil + +# From the end +array[-1] #=> 5 + +# With a start and end index +array[2, 4] #=> [3, 4, 5] + +# Or with a range +array[1..3] #=> [2, 3, 4] + +# Add to an array like this +array << 6 #=> [1, 2, 3, 4, 5, 6] + +# Hashes are Ruby's primary dictionary with keys/value pairs. +# Hashes are denoted with curly braces: +hash = {'color' => 'green', 'number' => 5} + +hash.keys #=> ['color', 'number'] + +# Hashes can be quickly looked up by key: +hash['color'] #=> 'green' +hash['number'] #=> 5 + +# Asking a hash for a key that doesn't exist returns nil: +hash['nothing here'] #=> nil + +# Iterate over hashes with the #each method: +hash.each do |k, v| + puts "#{k} is #{v}" +end + +# Since Ruby 1.9, there's a special syntax when using symbols as keys: + +new_hash = { defcon: 3, action: true} + +new_hash.keys #=> [:defcon, :action] + +# Tip: Both Arrays and Hashes are Enumerable +# This means they share a lot of useful methods such as each, map, count, and more + +# Control structures + +if true + "if statement" +elsif false + "else if, optional" +else + "else, also optional" +end + +for counter in 1..5 + puts "iteration #{counter}" +end +#=> iteration 1 +#=> iteration 2 +#=> iteration 3 +#=> iteration 4 +#=> iteration 5 + +# HOWEVER +# No-one uses for loops +# Use `each` instead, like this: + +(1..5).each do |counter| + puts "iteration #{counter}" +end +#=> iteration 1 +#=> iteration 2 +#=> iteration 3 +#=> iteration 4 +#=> iteration 5 + +counter = 1 +while counter <= 5 do + puts "iteration #{counter}" +end +#=> iteration 1 +#=> iteration 2 +#=> iteration 3 +#=> iteration 4 +#=> iteration 5 + +grade = 'B' + +case grade +when 'A' + puts "Way to go kiddo" +when 'B' + puts "Better luck next time" +when 'C' + puts "You can do better" +when 'D' + puts "Scraping through" +when 'F' + puts "You failed!" + + +# Functions + +def double(x) + x * 2 +end + +# Functions (and all blocks) implcitly return the value of the last statement +double(2) #=> 4 + +# Parentheses are optional where the result is unambiguous +double 3 #=> 6 + +double double 3 #=> 12 + +def sum(x,y) + x + y +end + +# Method arguments are separated by a comma +sum 3, 4 #=> 7 + +sum sum(3,4), 5 #=> 12 + +# yield +# All methods have an implicit, optional block parameter +# it can be called with the 'yield' keyword + +def surround + puts "{" + yield + puts "}" +end + +surround { puts 'hello world' } + +# { +# hello world +# } + + +# Define a class with the class keyword +class Human + + # A class variable. It is shared by all instances of this class. + @@species = "H. sapiens" + + # Basic initializer + def initialize(name, age=0): + # Assign the argument to the "name" instance variable for the instance + @name = name + # If no age given, we will fall back to the default in the arguments list. + @age = age + end + + # Basic setter method + def name=(name) + @name = name + end + + # Basic getter method + def name + @name + end + + # A class method; uses self to distinguish from instance methods. (Can only be called on class, not an instance). + + def self.say(msg) + puts "#{msg}" + end + + def species + @@species + end + +end + + +# Instantiate a class +jim = Human.new("Jim Halpert") + +dwight = Human.new("Dwight K. Schrute") + +# Let's call a couple of methods +jim.species #=> "H. sapiens" +jim.name #=> "Jim Halpert" +dwight.species #=> "H. sapiens" +dwight.name #=> "Dwight K. Schrute" + +# Call the class method +Human.say("Hi") #=> "Hi" +```
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