Re: Need help with a macro

[Andy Wingo <wingo@pobox.com>]

Hello,

On Sun 15 Nov 2009 17:33, Josef Wolf <jw@raven.inka.de> writes:

> Hello,
>
> I am trying to work through the little schemer book. In order to make it
> easier to go through the examples, I've come up with the following macro:
>
>   ;;; Helper to visualize
>
>   (define-macro (disp exp)
>     (display exp)   (newline)
>     `(display ,exp)
>   ;  (newline)  (newline)
>   )

Does the little schemer book actually use defmacro?

Anyway the issue is that defmacro needs to return Scheme code as an
s-expression. The last expression in a function is its return value.
That would be the `(display ,exp) bit there. But if you uncomment the
newlines, well, you return whatever newline returns, which is actually
unspecified.

Good luck,

Andy
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