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diff --git a/paren.html.markdown b/paren.html.markdown new file mode 100644 index 00000000..778598ce --- /dev/null +++ b/paren.html.markdown @@ -0,0 +1,193 @@ +--- + +language: Paren +filename: learnparen.paren +contributors: + - ["KIM Taegyoon", "https://github.com/kimtg"] +--- + +[Paren](https://bitbucket.org/ktg/paren) is a dialect of Lisp. It is designed to be an embedded language. + +Some examples are from http://learnxinyminutes.com/docs/racket/ . + +```lisp +;;; Comments +# comments + +;; Single line comments start with a semicolon or a sharp sign + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; 1. Primitive Datatypes and Operators +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +;;; Numbers +123 ; int +3.14 ; double +6.02e+23 ; double +(int 3.14) ; => 3 : int +(double 123) ; => 123 : double + +;; Function application is written (f x y z ...) +;; where f is a function and x, y, z, ... are operands +;; If you want to create a literal list of data, use (quote) to stop it from +;; being evaluated +(quote (+ 1 2)) ; => (+ 1 2) +;; Now, some arithmetic operations +(+ 1 1) ; => 2 +(- 8 1) ; => 7 +(* 10 2) ; => 20 +(^ 2 3) ; => 8 +(/ 5 2) ; => 2 +(% 5 2) ; => 1 +(/ 5.0 2) ; => 2.5 + +;;; Booleans +true ; for true +false ; for false +(! true) ; => false +(&& true false (prn "doesn't get here")) ; => false +(|| false true (prn "doesn't get here")) ; => true + +;;; Characters are ints. +(char-at "A" 0) ; => 65 +(chr 65) ; => "A" + +;;; Strings are fixed-length array of characters. +"Hello, world!" +"Benjamin \"Bugsy\" Siegel" ; backslash is an escaping character +"Foo\tbar\r\n" ; includes C escapes: \t \r \n + +;; Strings can be added too! +(strcat "Hello " "world!") ; => "Hello world!" + +;; A string can be treated like a list of characters +(char-at "Apple" 0) ; => 65 + +;; Printing is pretty easy +(pr "I'm" "Paren. ") (prn "Nice to meet you!") + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; 2. Variables +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; You can create or set a variable using (set) +;; a variable name can use any character except: ();#" +(set some-var 5) ; => 5 +some-var ; => 5 + +;; Accessing a previously unassigned variable is an exception +; x ; => Unknown variable: x : nil + +;; Local binding: Use lambda calculus! `a' and `b' are bound to `1' and `2' only within the (fn ...) +((fn (a b) (+ a b)) 1 2) ; => 3 + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; 3. Collections +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +;;; Lists + +;; Lists are vector-like data structures. (Random access is O(1).) +(cons 1 (cons 2 (cons 3 (list)))) ; => (1 2 3) +;; `list' is a convenience variadic constructor for lists +(list 1 2 3) ; => (1 2 3) +;; and a quote can also be used for a literal list value +(quote (+ 1 2)) ; => (+ 1 2) + +;; Can still use `cons' to add an item to the beginning of a list +(cons 0 (list 1 2 3)) ; => (0 1 2 3) + +;; Lists are a very basic type, so there is a *lot* of functionality for +;; them, a few examples: +(map inc (list 1 2 3)) ; => (2 3 4) +(filter (fn (x) (== 0 (% x 2))) (list 1 2 3 4)) ; => (2 4) +(length (list 1 2 3 4)) ; => 4 + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; 3. Functions +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +;; Use `fn' to create functions. +;; A function always returns the value of its last expression +(fn () "Hello World") ; => (fn () Hello World) : fn + +;; Use parentheses to call all functions, including a lambda expression +((fn () "Hello World")) ; => "Hello World" + +;; Assign a function to a var +(set hello-world (fn () "Hello World")) +(hello-world) ; => "Hello World" + +;; You can shorten this using the function definition syntatcic sugae: +(defn hello-world2 () "Hello World") + +;; The () in the above is the list of arguments for the function +(set hello + (fn (name) + (strcat "Hello " name))) +(hello "Steve") ; => "Hello Steve" + +;; ... or equivalently, using a sugared definition: +(defn hello2 (name) + (strcat "Hello " name)) + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; 4. Equality +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +;; for numbers use `==' +(== 3 3.0) ; => true +(== 2 1) ; => false + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; 5. Control Flow +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +;;; Conditionals + +(if true ; test expression + "this is true" ; then expression + "this is false") ; else expression +; => "this is true" + +;;; Loops + +;; for loop is for number +;; (for SYMBOL START END STEP EXPR ..) +(for i 0 10 2 (pr i "")) ; => prints 0 2 4 6 8 10 +(for i 0.0 10 2.5 (pr i "")) ; => prints 0 2.5 5 7.5 10 + +;; while loop +((fn (i) + (while (< i 10) + (pr i) + (++ i))) 0) ; => prints 0123456789 + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; 6. Mutation +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +;; Use `set' to assign a new value to a variable or a place +(set n 5) ; => 5 +(set n (inc n)) ; => 6 +n ; => 6 +(set a (list 1 2)) ; => (1 2) +(set (nth 0 a) 3) ; => 3 +a ; => (3 2) + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; 7. Macros +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +;; Macros let you extend the syntax of the language. +;; Paren macros are easy. +;; In fact, (defn) is a macro. +(defmacro setfn (name ...) (set name (fn ...))) +(defmacro defn (name ...) (def name (fn ...))) + +;; Let's add an infix notation +(defmacro infix (a op ...) (op a ...)) +(infix 1 + 2 (infix 3 * 4)) ; => 15 + +;; Macros are not hygienic, you can clobber existing variables! +;; They are code transformations. +``` |