From 273fa8606b662dbec5b3b0b2fd0d3dfd648e00ab Mon Sep 17 00:00:00 2001 From: Geoffrey Liu Date: Sun, 26 Jun 2016 21:21:13 +0800 Subject: [racket/en] Add more details about Racket (#2278) * Add let* and letrec reference * More elaboration on structs * Add code about predefined car, cdr functions * Mention explicit typing, int to real conversion --- racket.html.markdown | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) (limited to 'racket.html.markdown') diff --git a/racket.html.markdown b/racket.html.markdown index 0fe3f030..96dcaf25 100644 --- a/racket.html.markdown +++ b/racket.html.markdown @@ -114,18 +114,42 @@ some-var ; => 5 "Alice" me) ; => "Bob" +;; let* is like let, but allows you to use previous bindings in creating later bindings +(let* ([x 1] + [y (+ x 1)]) + (* x y)) + +;; finally, letrec allows you to define recursive and mutually recursive functions +(letrec ([is-even? (lambda (n) + (or (zero? n) + (is-odd? (sub1 n))))] + [is-odd? (lambda (n) + (and (not (zero? n)) + (is-even? (sub1 n))))]) + (is-odd? 11)) + ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; 3. Structs and Collections ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; Structs +; By default, structs are immutable (struct dog (name breed age)) (define my-pet (dog "lassie" "collie" 5)) my-pet ; => # +; returns whether the variable was constructed with the dog constructor (dog? my-pet) ; => #t +; accesses the name field of the variable constructed with the dog constructor (dog-name my-pet) ; => "lassie" +; You can explicitly declare a struct to be mutable with the #:mutable option +(struct rgba-color (red green blue alpha) #:mutable) +(define burgundy + (rgba-color 144 0 32 1.0)) +(set-color-green! burgundy 10) +(color-green burgundy) ; => 10 + ;;; Pairs (immutable) ;; `cons' constructs pairs, `car' and `cdr' extract the first ;; and second elements @@ -143,6 +167,16 @@ my-pet ; => # ;; and a quote can also be used for a literal list value '(1 2 3) ; => '(1 2 3) +;; Racket has predefined functions on top of car and cdr, to extract parts of a list +(cadr (list 1 2 3)) ; => 2 +(car (cdr (list 1 2 3))) ; => 2 + +(cddr (list 1 2 3)) ; => '(3) +(cdr (cdr (list 1 2 3))) ; => '(3) + +(caddr (list 1 2 3)) ; => 3 +(car (cdr (cdr (list 1 2 3)))) ; => 3 + ;; Can still use `cons' to add an item to the beginning of a list (cons 4 '(1 2 3)) ; => '(4 1 2 3) -- cgit v1.2.3 From 51ce7fda40f3c951b807971587374c56fa9d7916 Mon Sep 17 00:00:00 2001 From: Derek Date: Wed, 30 Nov 2016 15:36:56 -0500 Subject: [racket/en] Expand list section (#2588) * Expand list section * Update backtick --- racket.html.markdown | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) (limited to 'racket.html.markdown') diff --git a/racket.html.markdown b/racket.html.markdown index 96dcaf25..38335bc1 100644 --- a/racket.html.markdown +++ b/racket.html.markdown @@ -164,10 +164,17 @@ my-pet ; => # (cons 1 (cons 2 (cons 3 null))) ; => '(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 +;; a quote can also be used for a literal list value '(1 2 3) ; => '(1 2 3) +;; a quasiquote (represented by the backtick character) with commas +;; can be used to evaluate functions +`(1 ,(+ 1 1) 3) ; => '(1 2 3) -;; Racket has predefined functions on top of car and cdr, to extract parts of a list +;; With lists, car/cdr work slightly differently +(car '(1 2 3)) ; => 1 +(cdr '(1 2 3)) ; => '(2 3) + +;; Racket also has predefined functions on top of car and cdr, to extract parts of a list (cadr (list 1 2 3)) ; => 2 (car (cdr (list 1 2 3))) ; => 2 -- cgit v1.2.3 From 51e14b0e341d5df2fb1bf9174e2c9b7016a4c07c Mon Sep 17 00:00:00 2001 From: Steve Chae Date: Thu, 27 Apr 2017 12:21:10 -0400 Subject: [racket/en] Fix Incorrect Names in Mutable Struct Examples (per Issue #2714) (#2715) * Fix wrong mutable struct namee * Re-added space after ; --- racket.html.markdown | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'racket.html.markdown') diff --git a/racket.html.markdown b/racket.html.markdown index 38335bc1..c6b1deba 100644 --- a/racket.html.markdown +++ b/racket.html.markdown @@ -147,8 +147,8 @@ my-pet ; => # (struct rgba-color (red green blue alpha) #:mutable) (define burgundy (rgba-color 144 0 32 1.0)) -(set-color-green! burgundy 10) -(color-green burgundy) ; => 10 +(set-rgba-color-green! burgundy 10) +(rgba-color-green burgundy) ; => 10 ;;; Pairs (immutable) ;; `cons' constructs pairs, `car' and `cdr' extract the first -- cgit v1.2.3