[racket] Is this a good design

[ROELOF WOBBEN]

Hello,

I am now in the book How to design a programm second edition at the point I have to design functions.

Now I wonder if I understand this part right so I have made this function.

;String -> String
;This function takes out the first character of a given string with the name s
; given "roelof" expect "r"
; given "example" expect "e"
(define (string_first s)
  ( if (eq? (string? s) true) (string-ith  s 0 )"You have not entered a string"))

So I hope somone can give me feedback on my first attempt so i can learn from it.

Regards,

Roelof

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