iskm/learnxinyminutes-docs
1
0
Fork 0
mirror of https://github.com/adambard/learnxinyminutes-docs.git synced 2024-12-23 09:41:36 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

corrections and suggestions

Browse Source
This commit is contained in:
Manu 2013-07-15 14:44:48 +12:00
parent 150b232b9b
commit 13604e7932
1 changed files with 116 additions and 43 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

159
racket.html.markdown
View File

@ -11,11 +11,19 @@ Feedback is appreciated! You can reach me at [@th3rac25](http://twitter.com/th3r
```racket
#lang racket ; defines the language we are using
;;; Comments
; Single line comments start with a semicolon
#| Multiline strings can be written
using three "'s, and are often used
as comments
#| Block comments
can span multiple lines and...
#|
they can be nested !
|#
|#
; S-expression comments discard the following expression
#; "this expression will be discarded" "2nd expression" ; => "2nd expression"
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 1. Primitive Datatypes and Operators
@ -46,12 +54,10 @@ Feedback is appreciated! You can reach me at [@th3rac25](http://twitter.com/th3r
;;; Booleans
#t ; for true
#f ; for false
#f ; for false -- any value other than #f is true
(not #t) ; => #f
; Equality for numbers is =
(= 1 1.0) ; => #t
(= 2 1) ; => #f
(and 0 #f (error "doesn't get here")) ; => #f
(or #f 0 (error "doesn't get here")) ; => 0
;;; Characters
#\A ; => #\A
@ -83,9 +89,9 @@ Feedback is appreciated! You can reach me at [@th3rac25](http://twitter.com/th3r
(define some-var 5)
some-var ; => 5
; Use set! to assign a new value to an existing variable
(set! some-var 6)
some-var ; => 6
; You can also use unicode characters
(define ⊆ subset?)
(⊆ (set 3 2) (set 1 2 3)); => #t
; Accessing a previously unassigned variable is an exception
;x ; => x: undefined ...
@ -107,18 +113,17 @@ my-pet ; => #<dog>
(dog? my-pet) ; => #t
(dog-name my-pet) ; => "lassie"
; Pairs
;;; Pairs (immutable)
; "cons" constructs pairs, "car" and "cdr" extract the first
; and second elements
(cons 1 2) ; => '(1 . 2)
(car (cons 1 2)) ; => 1
(cdr (cons 1 2)) ; => 2
; Lists are linked-list data structures
'(1 2 3) ; => '(1 2 3)
;;; Lists
; Vectors are fixed-length arrays
#(1 2 3) ; => '#(1 2 3)
; Lists are linked-list data structures
(list 1 2 3) ; => '(1 2 3)
; Use "cons" to add an item to the beginning of a list
(cons 4 '(1 2 3)) ; => (4 1 2 3)
@ -126,14 +131,13 @@ my-pet ; => #<dog>
; Use "append" to add lists together
(append '(1 2) '(3 4)) ; => (1 2 3 4)
; Use "filter", "map" to interact with collections
(map add1 '(1 2 3)) ; => (2 3 4)
(filter even? '(1 2 3)) ; => (2)
;;; Vectors
; Use "fold" to reduce them
(foldl + 0 '(1 2 3 4))
; = (+ 1 (+ 2 (+ 3 (+ 4 0)))
; => 10
; Vectors are fixed-length arrays
#(1 2 3) ; => '#(1 2 3)
; Use "vector-append" to add vectors together
(vector-append #(1 2 3) #(4 5 6)) ; => #(1 2 3 4 5 6)
;;; Sets
@ -218,7 +222,24 @@ m ; => '#hash((b . 2) (a . 1) (c . 3))
; => "Hello Finn, you passed 3 extra args"
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 4. Control Flow
;; 4. Equality
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; for numbers use "="
(= 3 3.0) ; => #t
(= 2 1) ; => #f
; for object identity use "eq?"
(eq? 3 3) ; => #t
(eq? 3 3.0) ; => #f
(eq? (list 3) (list 3)) ; => #f
; for collections use "equal?"
(equal? (list 'a 'b) (list 'a 'b)) ; => #t
(equal? (list 'a 'b) (list 'b 'a)) ; => #f
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 5. Control Flow
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Conditionals
@ -254,6 +275,7 @@ m ; => '#hash((b . 2) (a . 1) (c . 3))
;;; Loops
; looping can be done through recursion
(define (loop i)
(when (< i 10)
(printf "i:~a~n" i)
@ -261,11 +283,26 @@ m ; => '#hash((b . 2) (a . 1) (c . 3))
(loop 5) ; => i:5 i:6 ...
; similarly, with a named let
(let loop ((i 0))
(when (< i 10)
(printf "i:~a~n" i)
(loop (add1 i)))) ; => i:0 i:1 ...
;;; Comprehensions
(for/list ([i '(1 2 3)])
(add1 i)) ; => '(2 3 4)
(for/list ([i '(1 2 3)] #:when (even? i))
i) ; => '(2)
(for/hash ([i '(1 2 3)])
(values i (number->string i))) ; => '#hash((1 . "1") (2 . "2") (3 . "3"))
; To combine iteration results, use "for/fold"
(for/fold ([sum 0]) ([i '(1 2 3 4)])
(+ sum i)) ; => 10
;;; Sequences
@ -286,7 +323,6 @@ m ; => '#hash((b . 2) (a . 1) (c . 3))
(for ([(k v) (in-hash (hash 'a 1 'b 2 'c 3 ))])
(printf "key:~a value:~a ~n" k v))
;;; Exceptions
; To catch an exception, use the "with-handlers" form
@ -297,7 +333,25 @@ m ; => '#hash((b . 2) (a . 1) (c . 3))
(raise "infinity"))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 5. Modules
;; 6. Mutation
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Use set! to assign a new value to an existing variable
(define n 5)
(set! n 6)
n ; => 6
; Many Racket datatypes can be immutable or mutable
; (Pairs, Lists, Strings, Vectors, Hash Tables, etc...)
; Use "vector" to create a mutable vector
(define vec (vector 2 2 3 4))
; Use vector-set! to update a slot
(vector-set! vec 0 1)
vec ; => #(1 2 3 4)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 7. Modules
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Modules let you organize code into multiple files and reusable libraries
@ -322,7 +376,7 @@ m ; => '#hash((b . 2) (a . 1) (c . 3))
;(show "~a" 1 #\A) ; => error, "show" was not exported
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 6. Classes and Objects
;; 8. Classes and Objects
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Create a class fish%
@ -330,19 +384,12 @@ m ; => '#hash((b . 2) (a . 1) (c . 3))
(class object%
(init size) ; initialization argument
(super-new) ; superclass initialization
(define current-size size) ; field
; Field
(define current-size size)
; Public methods
(define/public (get-size)
current-size)
(define/public (grow amt)
(set! current-size (+ amt current-size)))
(define/public (eat other-fish)
(grow (send other-fish get-size)))))
(define/public (get-size) current-size)
(define/public (grow amt) (set! current-size (+ amt current-size)))
(define/public (eat other-fish) (grow (send other-fish get-size)))))
; Create an instance of fish%
(define charlie
@ -352,9 +399,8 @@ m ; => '#hash((b . 2) (a . 1) (c . 3))
(send charlie grow 6)
(send charlie get-size) ; => 16
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 7. Macros
;; 9. Macros
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Macros let you extend the syntax of the language
@ -363,7 +409,7 @@ m ; => '#hash((b . 2) (a . 1) (c . 3))
(unless (even? 10) "odd" "even") ; => "even"
; Macros are hygienic, there is no risk to clobber existing variables!
; Macros are hygienic, you cannot clobber existing variables!
(define-syntax-rule (swap x y)
(begin
(define tmp x)
@ -374,7 +420,34 @@ m ; => '#hash((b . 2) (a . 1) (c . 3))
(define a 2)
(define b 3)
(swap a b)
(printf "tmp = ~a; a = ~a; b = ~a" tmp a b) ; tmp is unaffected by swap
(printf "tmp = ~a; a = ~a; b = ~a~n" tmp a b) ; tmp is unaffected by swap
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 10. Contracts
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Contracts impose constraints on values exported from modules
(module bank-account racket
(provide (contract-out
[deposit (-> positive? any)] ; amount will always be a positive number
[balance (-> positive?)]))
(define amount 0)
(define (deposit a) (set! amount (+ amount a)))
(define (balance) amount)
)
(require 'bank-account)
(deposit 5)
(balance) ; => 5
; Any client that attempt to deposit a non-positive amount, will be blamed
; (deposit -5) ; => deposit: contract violation
; expected: positive?
; given: -5
; more details....
```
## Further Reading