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Use or not, of lambda to define a function in Racket


Use or not, of lambda to define a function in Racket

By : user2172646
Date : October 23 2020, 08:10 AM
Hope this helps As said in the comments, you don't need to use lambda. It is perhaps more conventional and convenient to use the non-lambda version to define a function
If you use the macro stepper in DrRacket, you can see how your program is expanded. (define (factorial1 number) etc.) becomes the following:
code :
(define-values (factorial1)
 (lambda (number)
   (if (#%app not (#%app number? number))
     (let-values () (#%app error 'factorial1 (quote "number is not a number")))
     (if (#%app equal? number (quote 0))
       (let-values () (quote 1))
       (let-values () (#%app * number (#%app factorial1 (#%app - number (quote 1)))))))))


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racket create function/lambda in let

racket create function/lambda in let


By : user3148761
Date : March 29 2020, 07:55 AM
may help you . For something like this, it's probably more idiomatic in Racket to just use define. You can declare a function within your existing function, then use it as normal.
code :
(define/public (get-rects)
  (define (wrap-edge coords)
    (append coords tetramino-wh))
  (case current-type
    [(0) (vector
          (wrap-edge (list 0 0))
          (wrap-edge (list tetramino-w 0))
          (wrap-edge (list (* 2 tetramino-w) 0))
          (wrap-edge (list (* 3 tetramino-w) 0)))]))
racket: (my-filter p lst) function with lambda and foldr

racket: (my-filter p lst) function with lambda and foldr


By : wang jie
Date : March 29 2020, 07:55 AM
this will help I am trying to implement a function (my-filter p lst) by using lambda, map and foldr. , First we need to see how foldr works.
code :
  (foldr k e '(1 2 3))
= (k 1 (k 2 (k 3 e)))
  (foldr cons empty '(1 2 3))
= (cons 1 (cons 2 (cons 3 empty)))
= (list 1 2 3)
(define (kons x xs)
  (if (p x)           ; where p is the predicate
      (cons x xs)
      xs))
 (foldr kons empty '(1 2 3))
#lang racket

(define p odd?)

(define (kons x xs)
  (if (p x)
      (cons x xs)
      xs))

(foldr kons empty '(1 2 3 4 5 6))
 '(1 3 5)
(define (my-filter p xs)
   (define (kons x xs) ...)
   (foldr ...))
Using λ to define function in Racket

Using λ to define function in Racket


By : Jagmeet singh
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , Yes, but you need to define it like you would with any other identifier.
code :
(define (testfn2)
  (define contains (λ (sl item) (ormap (λ(x)(equal? item x)) sl)))
  (if (contains (list 1 2 3) 2)    "yes" "no"))
Why define-values is not bound in a Racket macro with #lang racket/base?

Why define-values is not bound in a Racket macro with #lang racket/base?


By : patric
Date : March 29 2020, 07:55 AM
Hope this helps Use (require (for-syntax racket/base)) to import racket/base also at phase 1 (compile time). Using #lang racket/base provides define-values only at phase 0 (runtime).
Dr racket define error in student language. define: expected only one expression for the function body, but found 3 extr

Dr racket define error in student language. define: expected only one expression for the function body, but found 3 extr


By : Jamie
Date : March 29 2020, 07:55 AM
Hope this helps Your code is OK for Scheme/Racket. However Student Language is a subset of Scheme, highly limited so it's easier for beginners. It's also used in How To Design Programs book. You can read more about Student Languages (actually there is five of them) on https://docs.racket-lang.org/htdp-langs/index.html.
In case of define there are important limitations:
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