Op 2-3-2012 9:51, Danny Yoo schreef:
> I did some study on that chapter but I cannnot make it work,
> This is what I have so far :
>
> ;;String -> String
> ;; Get the first character of a string (s) if there is one. error
otherwise.
> ;; given "aaaa" expected "a"
> ;; given "" expected "
> (define (first-string s)
> (cond
> [(eq? s "") (error "first-string" "Empty string found")] ;;
check for a empty string.if so put a error message
> [(and (string? s) (not(eq? s ""))) (string-ith s 0)]
;; if it's a non-empty string then do the trick.
> [(number? s) (error "first-string" "No string found")] ;; if
it's a number then put a error message
> [(boolean? s) (error "first-string" "No string found")] ;; if
it's a boolean then put a error message
> [(image? s) (error "first string" "No string found")] ;;
if it's a image put a error message
> ))
>
> But when I do (first-string ") then still DrRacket gives his own
error message instead of the one I made.
> Any tips are welcome here.
What is the exact content of the error message that DrRacket gives you?
Very wierd.
On my windows box I see this message appear : string-ith: expected an
exact integer in [0, length of the given string] for the second
argument, but received 0
On my linux box it worked well and I see what I expected.
Roelof
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