Re: Repeat syntax

[Matt Wette]

> On Nov 24, 2017, at 9:05 PM, Christopher Howard <address@hidden> wrote:
> 
> 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?
> 
> -- 
> https://emailselfdefense.fsf.org/en/

you probably want named let

((_ n exp exp* ...)
 (let loop ((n n))
     (unless (<= n 0)
        exp exp* ...
        (loop (1- n)))