I came to the following result as conversion function :
#lang typed/racket
(: string2value (-> String Integer))
(define (string2value astring)
(define (fun [val : Char] [res : Integer])
(+ (* 10 res) (- (char->integer val) 48)))
(foldl fun 0 (string->list astring))
)
(print (string2value "12345"))
On Tuesday, February 11, 2020 at 11:34:16 AM UTC+1, Alain De Vos wrote:
>
> I tried the following function to conver a String to an Integer.
>
> #lang typed/racket
> (: myconversion (-> String Integer))
> (define (myconversion str)
> (string->number str))
>
> The error given is :
> Type Checker: type mismatch
> expected: Integer
> given: (U Complex False) in: (string->number str)
>
> I guess this is because a number is not an Integer.
>
> How to proceed?
>
> I found the following code on internet , but this looks like a real
> overkill for this simple problem ,
>
> (: numerical-char->integer (-> Char
> Integer))(define (numerical-char->integer char)
> (let ([num (- (char->integer char) 48)]) ; 48 = (char->integer #\0)
> (if
> (or (< num 0) (> num 9))
> (raise 'non-numerical-char #t)
> num)))
> (: string->integer (-> String
> Integer))(define (string->integer str)
> (let ([char-list (string->list str)])
> (if (null? char-list)
> (raise 'empty-string #t)
> (foldl
> (λ([x : Integer] [y : Integer])
> (+ (* y 10) x))
> 0
> (map numerical-char->integer char-list)))))
>
>
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