Re: records

[David Van Horn]

Ian Zimmerman wrote:
> Instead, I itch to write
>
> (let ((foo-rtd (make-record-type "foo" 'bar 'baz)))
>   (define foo? (record-predicate foo-rtd))
>   ...)
>
> but this of course doesn't work because the define is local. 

This is actually a Scheme FAQ:

   4.9 Is there a way to define top-level closures?
   http://www.schemers.org/Documents/FAQ/#N108F7

> What is the idiomatic way to do this?

You could use a macro:

   (define-syntax define-with
     (syntax-rules ()
       ((define-with ((i1 v1) ...) (i2 v2) ...)
        (begin
          (define i2 #f) ...
          (let ((i1 v1) ...)
            (set! i2 v2) ...)))))

Allowing you to write:

   (define-with ((foo-rtd (make-record-type "foo" 'bar 'baz)))
     (foo? (record-predicate foo-rtd))
     ...)

David