CODEWITHSUNDEEP
lispracket
Kero
Kero

Reputation: 1954

convert strings in list to numbers in racket?

Calling all racket developers, I am a newbie to racket language and function languages in general. Long story short, I have a nested list that contains numbers and string and I want to convert string elements to numbers.

Example: If I have list like this '( 3 "3"( 1 "1"()( 2 "2" () ()))( 5 "5" () () ))

I want to converted to '( 3 3( 1 1()( 2 2 () ()))( 5 5 () () ))
While maintaining the same shape, therefore I wrote this function 

(define (mapBst BST someFunct )
 (if (null? BST) '()
      (someFunct (car(cdr BST)) (mapBST someFunct (cdr (car BST))))
      )
  )
(mapBst  '( 3 "3"( 1 "1"()( 2 "2" () ()))( 5 "5" () () )) string->number)

But I am getting this error : cdr: contract violation expected: pair? given: 3

Any clue why I am getting this error or what I did wrong, any suggestions will help. Thank you in advance

Upvotes: 0

Views: 1714

Answers (1)

Brendan Cannell
Brendan Cannell

Reputation: 679

I suggest this:

(define (mapBST BST someFunct)
  (cond [(null? BST)
         '()]
        [(list? (car BST))
         (cons (mapBST (car BST) someFunct)
               (mapBST (cdr BST) someFunct))]
        [else
         (cons (someFunct (car BST))
               (mapBST (cdr BST) someFunct))]))

Example:

> (mapBST '( 3 "3"( 1 "1"()( 2 "2" () ()))( 5 "5" () () ))
          (λ (x) (if (string? x) (string->number x) x)))
'(3 3 (1 1 () (2 2 () ())) (5 5 () ()))

Upvotes: 1

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