Is there any way to make a lat using cons in scheme?

Question

I'm having this simple piece of code, constructing a list of numbers:

#lang scheme

(define pseudofizzbuzz (lambda (x)
             (cond
               ((zero? x) (quote ()))
               ((or (integer? (/ x 3)) (integer? (/ x 5))) (cons (quote ()) (pseudofizzbuzz (- x 1))))
               (else (cons x (pseudofizzbuzz (- x 1)))))))

(define reverselist (lambda (lat)
                  (cond
                    ((null? lat) (quote ()))
                    (else
                     (cons (reverselist (cdr lat)) (list (car lat))))))) 


(reverselist (pseudofizzbuzz 10))

And the result I get is:

 ((((((((((() 1) 2) ()) 4) ()) ()) 7) 8) ()) ())

But what I want of course is:

(1 2 4 7 8)

Is there any way to do it in scheme? I'm using DrRacket.

score 1 · Answer 1 · answered Dec 09 '16 at 17:59

1

Already found the answer:

 (define (flatten x)
    (cond ((null? x) '())
          ((not (pair? x)) (list x))
          (else (append (flatten (car x))
                        (flatten (cdr x))))))

answered Dec 09 '16 at 17:59

user7273921

43
4

score 1 · Accepted Answer · answered Dec 09 '16 at 18:07

Use (cons an-element a-list) to extend a-list with a new element an-element:

#lang racket

(define pseudofizzbuzz
  (lambda (x)
    (cond
      ((zero? x)
       (quote ()))
      ((or (integer? (/ x 3)) (integer? (/ x 5)))
       (pseudofizzbuzz (- x 1)))
      (else
       (cons x (pseudofizzbuzz (- x 1)))))))

(define reverselist
  (lambda (lat)
    (cond
      ((null? lat) 
       (quote ()))
      (else        
       (cons (reverselist (cdr lat)) (list (car lat))))))) 

(pseudofizzbuzz 10)

This produces the results in reverse order, so

(reverse (pseudofizzbuzz 10))

will give you the elements in the correct order.

Is there any way to make a lat using cons in scheme?

2 Answers2