Using string->number on a list containing strings and numbers

Question

I'm attempting to recursively parse through a list that contains numbers, strings, and null lists and convert any strings to numbers using string->number

(define tnode '(5 "5" () ()))

using the function

(define (test funct inlist)
    (cond((null? inlist) '())
         ((number? inlist) ((cons (car inlist) (test funct (cdr inlist)))))
         (else (cons (funct (car inlist)) (test funct (cdr inlist))))
         )
    )

as

(test string->number tnode)

however I am recieving a contract violation error on the first number 5 (and on the later null lists if I use a tnode with only strings and null lists). It seems as if the function is ignoring the first two conditions and going straight to the else statement. Why is this? I dont believe that there are any syntax errors as other cond functions ive tested have worked fine. I'm not quite sure what the issue is.

Scott Hunter · Accepted Answer · 2017-04-17 18:07:46Z

1

inlist is the whole list; you want to be checking the first element of it instead, just as you deal with the first element in your result.

answered Apr 17, 2017 at 18:07

Scott Hunter

50k12 gold badges64 silver badges107 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Hunter Tipton Over a year ago

Thank you, that helped with working around the numbers however the null lists are not appearing. I am getting an output of '(5 5) rather than '(5 5 () ()) as I need.

Hunter Tipton Over a year ago

I have figured out that the problem is, I needed both a condition for (null? inlist) and a condition for (null? (car inlist)) as there would need to be a final null value for it to work due to recurision final code is will be in another answer

Hunter Tipton · Accepted Answer · 2017-04-17 18:39:37Z

0

The funciton code that gave me the desired output was as follows

(define (test funct inlist)
    (cond((null? inlist) '())
         ((null? (car inlist)) (cons '() (test funct (cdr inlist))))
         ((number? (car inlist)) (cons (car inlist) (test funct (cdr inlist))))
         (else (cons (funct (car inlist)) (test funct (cdr inlist))))
         )
    )

answered Apr 17, 2017 at 18:39

Hunter Tipton

3331 gold badge4 silver badges12 bronze badges

Collectives™ on Stack Overflow

Using string->number on a list containing strings and numbers

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related