Re: Repeat syntax

[Alex Vong <alexvong1995@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1015 bytes --]

Christopher Howard <christopher.howard@qlfiles.net> writes:

> Hi list, I want to have a function
>
>   (repeat n exp exp* ...)
>
> That calls the expressions n times for side effect, like for-each, but
> without the bother of dealing with a list. It seems like somebody else
> must have thought of this before, but I couldn't find the equivalent
> procedure. After reading 6.10.2 I came up with this
>
> (define-syntax repeat
>   (syntax-rules (repeat)
>     ((_ n exp exp* ...)
>      '(unless (<= n 0)
>        exp
>        exp*
>        ...
>        (repeat (- n 1) exp exp* ...)))))
>
> Which doesn't work I think because repeat gets expanded infinitely many
> times. I was pondering other ways to do this, but they all seem to end
> in either infinite expansion, or an important variable getting
> overshadowed. So, could somebody point me in the right direction?

Do you want to evaluate the expressions during macro-expand-time or
run-time?

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 832 bytes --]