Novice question about Scheme

Question

When I try to run (define-type on DrScheme, I got error "reference to an identifier before its definition: define-type", what is it happening?

I input:

(define-type GUI
    [label (text string?)]
    [button (text string?)
            (enabled? boolean?)])

and I get result:

reference to an identifier before its definition: define-type

thanks.

Robert

Answer 1

define-type is not part of "basic" Scheme, it is part of "Typed Scheme". To use this language in Dr Scheme:

Make sure "Module" is selected in the dropdown at the bottom left of the window. Then in the top window, enter:

#lang typed-scheme

and press the "run" button.