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authorManu <manu.delab@gmail.com>2013-07-12 23:33:34 +1200
committerManu <manu.delab@gmail.com>2013-07-12 23:33:34 +1200
commitfb2c8aa765067bd2ff70d6bbabaf5304b849c3f3 (patch)
treefae480940c1658e318fa181c51be4ddebb52af48 /racket.html.markdown
parent80c2a00bc5502f3afb4c9f50ba8d8197f8dd7700 (diff)
added macros, conditionals. fixed some errors
Diffstat (limited to 'racket.html.markdown')
-rw-r--r--racket.html.markdown130
1 files changed, 99 insertions, 31 deletions
diff --git a/racket.html.markdown b/racket.html.markdown
index db85edb0..0d75e8a2 100644
--- a/racket.html.markdown
+++ b/racket.html.markdown
@@ -1,38 +1,43 @@
-TODO: sequences, control flow, macros, objects, modules
-
---
language: racket
-author: Th3rac25
+author: th3rac25
---
Racket is a general purpose, multi-paradigm programming language in the Lisp/Scheme family.
-Feedback would be highly appreciated! You can reach me at [@th3rac25](http://twitter.com/th3rac25) or th3rac25 [at] [google's email service]
+Feedback is appreciated! You can reach me at [@th3rac25](http://twitter.com/th3rac25) or th3rac25 [at] [google's email service]
```racket
+#lang racket ; defines the language we are using
+
+; TODO:
+; quote
+; collections (set, hash)
+; structs
+; control flow (pattern-matching, loops, sequences)
+; objects
+
+
; Single line comments start with a semicolon
#| Multiline strings can be written
using three "'s, and are often used
as comments
|#
-
-#lang racket ; defines the language we are using
-
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 1. Primitive Datatypes and Operators
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; You have numbers
-1
9999999999999999999999 ; big integers
-3.14
+3.14 ; reals
6.02e+23
-1/2 ; rationals
-1+2i ; complex numbers
+1/2 ; rationals
+1+2i ; complex numbers
-; Math is what you would expect
+; Operators are functions, functions applications are written
+; (f x y z ...) where f is a function and x, y, z, ... are operands
(+ 1 1) ; => 2
(- 8 1) ; => 7
(* 10 2) ; => 20
@@ -47,7 +52,6 @@ Feedback would be highly appreciated! You can reach me at [@th3rac25](http://twi
#t ; for true
#f ; for false
(not #t) ; => #f
-; In conditionals, all non-#f values are treated as true
; Equality for numbers is =
(= 1 1.0) ; => #t
@@ -76,23 +80,27 @@ Feedback would be highly appreciated! You can reach me at [@th3rac25](http://twi
(printf "I'm Racket. Nice to meet you!\n")
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-;; 2. Variables and Collections
+;; 2. Variables
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-
-; You need to declare variables before assigning to them.
+; You can create a variable using define
; a variable name can use any characters except: () [] {} " , ' ` ; # | \
(define some-var 5)
some-var ; => 5
-; use set! to reassign
+; Use set! to assign a new value to an existing variable
(set! some-var 6)
some-var ; => 6
; Accessing a previously unassigned variable is an exception
-x ; => x: undefined ...
+;x ; => x: undefined ...
+
+; Local binding: me is bound to "Bob" only within (let ...)
+(let ([me "Bob"])
+ "Alice"
+ me) ; => "Bob"
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-;; 3. Collections and Sequences
+;; 3. Collections
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Lists are linked-list data structures, vectors are fixed-length arrays.
@@ -114,28 +122,23 @@ x ; => x: undefined ...
; = (+ 1 (+ 2 (+ 3 (+ 4 0)))
; => 10
-; a sequence is an ordered collection of value
-(sequence? '(1 2 3)) ; => #t
-(sequence? #(1 2 3)) ; => #t
+; Set
+
-;; more sequence stuff here !
+; Hash
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 3. Functions
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-; Use fn to create new functions. A function always returns
+; Use lambda to create new functions. A function always returns
; its last statement.
(lambda () "Hello World") ; => #<procedure>
; (You need extra parens to call it)
((lambda () "Hello World")) ; => "Hello World"
-; You can create a variable using define
-(define x 1)
-x ; => 1
-
; Assign a function to a var
(define hello-world (lambda () "Hello World"))
(hello-world) ; => "Hello World"
@@ -171,12 +174,61 @@ x ; => 1
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 4. Control Flow
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; Conditionals
+(if #t ; test expression
+ "this is true" ; then expression
+ "this is false" ; else expression
+ ) ; => "this is true"
+
+; In conditionals, all non-#f values are treated as true
+(member "Groucho" '("Harpo" "Groucho" "Zeppo")) ; => '("Groucho" "Zeppo")
+(if (member "Groucho" '("Harpo" "Groucho" "Zeppo"))
+ 'yep
+ 'nope) ; => 'yep
+
+
+; Cond chains a series of test to select a result
+(cond
+ [(> 2 2) (error "wrong!")]
+ [(< 2 2) (error "wrong again!")]
+ [else 'ok]) ; => 'ok
+; Pattern matching
+
+; Loops
+
+; Sequences
+
+; Exceptions
+; To catch an exception, use the with-handlers form
+; To throw an exception use raise
+(with-handlers
+ ([(lambda (v) (equal? v "infinity"))
+ (lambda (exn) +inf.0)])
+ (raise "infinity"))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 5. Modules
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-
+; Modules let you organize code into multiple files and reusable libraries.
+
+(module cake racket/base ;; define a new module 'cake' based on racket/base
+
+ (provide print-cake) ;; function exported by the module
+
+ (define (print-cake n)
+ (show " ~a " n #\.)
+ (show " .-~a-. " n #\|)
+ (show " | ~a | " n #\space)
+ (show "---~a---" n #\-))
+
+ (define (show fmt n ch) ;; internal function
+ (printf fmt (make-string n ch))
+ (newline)))
+
+(require 'cake) ;; import all 'cake' functions
+(print-cake 3)
+;(show "~a" 1 #\A) ; => this is an error
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 6. Classes
@@ -186,8 +238,24 @@ x ; => 1
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 7. Macros
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-
-
+; Macros let you extend the syntax of the language
+(define-syntax-rule (unless test then else)
+ (if test else then))
+
+(unless (even? 10) "odd" "even") ; => "even"
+
+; Macros are hygienic, there is no risk to clobber existing variables!
+(define-syntax-rule (swap x y)
+ (begin
+ (define tmp x)
+ (set! x y)
+ (set! y tmp)))
+
+(define tmp 1)
+(define a 2)
+(define b 3)
+(swap a b)
+(printf "tmp = ~a; a = ~a; b = ~a" tmp a b) ; tmp is unaffected by swap
```
;; Further Reading