[plt-scheme] stupid Swindle tricks

On May 26, Doug Orleans wrote:
> Candidates for swindle/misc.ss, in decreasing order of usefulness:
> 
>   (defsyntax* set-if!
>     (syntax-rules ()
>       ((_ condition then-place else-place val)
>        (if condition (set! then-place val) (set! else-place val)))))

I thought about adding that at the time, but there was some reason not
to do it.  Possibly the double code output in `val'.


>   (defsyntax* last-of
>     (syntax-rules ()
>       ((_ successor first clause ...)
>        (collect (x first (successor x)) clause ...))))
> 
>   (define* (nth-of n successor first)
>     (last-of successor first (i <- 0 ..< n)))
> 
>   (defsyntax* set-nth-of!
>     (syntax-rules ()
>       ((_ n successor first val)
>        (let ((nn n))
> 	 (set! (if (zero? nn)
> 		   first
> 		   (successor (nth-of (1- nn) successor first)))
> 	       val)))))

(These seem too specific.)


>   (defsyntax* push-at-end!
>     (syntax-rules ()
>       ((_ val place)
>        (set! (nth-of (length place) cdr place) (list val)))))
> 
>   (defsyntax* pop-at-end!
>     (syntax-rules ()
>       ((_ place)
>        (begin0 (last place)
> 	       (set! (nth-of (1- (length place)) cdr place) null)))))

Again, they seem too specific, and easy to implement yourself.  BTW,
I'd use a simple `append!' for the first, and a simple loop for the
second.

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                  http://www.barzilay.org/                 Maze is Life!