Indeed good question, but the following code works,
#lang typed/racket
(require typed/racket/gui)
(: fib (-> Integer Integer))
(define (fib n)
(if (< 2 n)
n
(+ (fib (- n 1))
(fib (- n 2)))))
(: numericalchar2integer (-> Char Integer))
(define (numericalchar2integer char)
(let ([num (- (char->integer char) 48)]) ; 48 = (char->integer #\0)
(if
(or (< num 0) (> num 9))
(raise 'non-numerical-char #t)
num)))
(: string2integer (-> String Integer))
(define (string2integer 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 numericalchar2integer char-list)))))
And the following code fails , just one the first line difference,
#lang
<https://docs.racket-lang.org/guide/Module_Syntax.html#%28part._hash-lang%29>
sweet-exp <https://docs.racket-lang.org/sweet/index.html> typed/racket
(: fib (-> Integer Integer))
(define (fib n)
(if (< 2 n)
n
(+ (fib (- n 1))
(fib (- n 2)))))
(: numericalchar2integer (-> Char Integer))
(define (numericalchar2integer char)
(let ([num (- (char->integer char) 48)]) ; 48 = (char->integer #\0)
(if
(or (< num 0) (> num 9))
(raise 'non-numerical-char #t)
num)))
(: string2integer (-> String Integer))
(define (string2integer 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 numericalchar2integer char-list)))))
Error, unbound identifier y.
Has sweet-exp a problem with lambda functions ?
On Tuesday, February 11, 2020 at 12:02:46 PM UTC+1, Ryan Culpepper wrote:
>
> What should `(myconversion "apple")` return?
> What should `(myconversion "12.3")` return?
> What does `string->number` do in each of those cases?
>
> Ryan
>
>
> On Tue, Feb 11, 2020 at 11:34 AM Alain De Vos <devosa...@gmail.com
> <javascript:>> 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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>> email to racket...@googlegroups.com <javascript:>.
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>>
>> <https://groups.google.com/d/msgid/racket-users/4a13bb2e-3107-4c5f-aee6-6d29e493c040%40googlegroups.com?utm_medium=email&utm_source=footer>
>> .
>>
>
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