[racket] Is this a good design

> 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?
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