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| -rw-r--r-- | racket.html.markdown | 45 |
1 files changed, 36 insertions, 9 deletions
diff --git a/racket.html.markdown b/racket.html.markdown index dfd30438..d3403ff8 100644 --- a/racket.html.markdown +++ b/racket.html.markdown @@ -204,44 +204,71 @@ m ; => '#hash((b . 2) (a . 1) (c . 3)) <-- no `d' ;; 3. Functions ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; -;; Use lambda to create new functions. -;; A function always returns its last statement. +;; Use `lambda' to create functions. +;; A function always returns the value of its last expression (lambda () "Hello World") ; => #<procedure> +;; Can also use a unicode `λ' +(λ () "Hellow World") ; => same function -;; (You need extra parens to call it) +;; Use parens to call all functions, including a lambda expression ((lambda () "Hello World")) ; => "Hello World" +((λ () "Hello World")) ; => "Hello World" ;; Assign a function to a var (define hello-world (lambda () "Hello World")) (hello-world) ; => "Hello World" -;; You can shorten this to: +;; You can shorten this using the function definition syntatcic sugae: (define (hello-world2) "Hello World") -;; The () is the list of arguments for the function. +;; The () in the above is the list of arguments for the function (define hello (lambda (name) (string-append "Hello " name))) (hello "Steve") ; => "Hello Steve" +;; ... or equivalently, using a sugared definition: +(define (hello2 name) + (string-append "Hello " name)) -;; You can have multi-variadic functions, too -(define hello2 +;; You can have multi-variadic functions too, using `case-lambda' +(define hello3 (case-lambda [() "Hello World"] [(name) (string-append "Hello " name)])) -(hello2 "Jake") ; => "Hello Jake" -(hello2) ; => "Hello World" +(hello3 "Jake") ; => "Hello Jake" +(hello3) ; => "Hello World" +;; ... or specify optional arguments with a default value expression +(define (hello4 [name "World"]) + (string-append "Hello " name)) ;; Functions can pack extra arguments up in a list (define (count-args . args) (format "You passed ~a args: ~a" (length args) args)) (count-args 1 2 3) ; => "You passed 3 args: (1 2 3)" +;; ... or with the unsugared `lambda' form: +(define count-args2 + (lambda args + (format "You passed ~a args: ~a" (length args) args))) ;; You can mix regular and packed arguments (define (hello-count name . args) (format "Hello ~a, you passed ~a extra args" name (length args))) (hello-count "Finn" 1 2 3) ; => "Hello Finn, you passed 3 extra args" +;; ... unsugared: +(define hello-count2 + (lambda (name . args) + (format "Hello ~a, you passed ~a extra args" name (length args)))) + +;; And with keywords +(define (hello-k #:name [name "World"] #:greeting [g "Hello"] . args) + (format "~a ~a, ~a extra args" g name (length args))) +(hello-k) ; => "Hello World, 0 extra args" +(hello-k 1 2 3) ; => "Hello World, 3 extra args" +(hello-k #:greeting "Hi") ; => "Hi World, 0 extra args" +(hello-k #:name "Finn" #:greeting "Hey") ; => "Hey Finn, 0 extra args" +(hello-k 1 2 3 #:greeting "Hi" #:name "Finn" 4 5 6) + ; => "Hi Finn, 6 extra args" ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;; 4. Equality |