XPost: comp.lang.scheme
B. Pym wrote:
Pascal Costanza wrote:
I'm not advocating tail-recursion instead of specialized iteration mechanisms closer to the problem domain. I'm just saying tail-
recursion code isn't anywhere as low-level as you're making it up to
be.
It actually is, and your posting below shows it very nicely.
Here is a nice example using loop:
(loop for (key value) on property-list by #'cddr
unless (member key excluded-keys)
append (list key value)) ; [1]
As a function:
(defun filter (excluded-keys property-list)
(loop for (key value) on property-list by #'cddr
unless (member key excluded-keys)
nconc (list key value)))
(filter '(c d) '(a 1 b 2 b 3 c 4 d 5 c 6))
(A 1 B 2 B 3)
The result is a correct property list
Gauche Scheme
(define (remove-props bad-keys prop-list)
(concatenate
(remove (^p (member (car p) bad-keys))
(slices prop-list 2))))
(remove-props '(c d) '(a 1 b 2 b 3 c 4 d 5 c 6))
===>
(a 1 b 2 b 3)
Nicolas Neuss wrote:
does this look like assembly?
(define (! n)
(let loop ((x n) (r 1))
(if (zero? x) r
(loop (- x 1) (* x r)))))
Yes, it does compared with
(defun factorial (n)
(loop for n from 1 upto n
and f = 1 then (* f n)
finally (return f)))
It's shorter using "do".
(define (fac n)
(do ((i 1 (+ 1 i))
(f 1 (* f i)))
((> i n) f)))
(fac 5)
===>
120
Paul Graham:
I consider Loop one of the worst flaws in CL, and an example
to be borne in mind by both macro writers and language designers.
Paul Graham, May 2001:
A hacker's language is terse and hackable. Common Lisp is not.
The good news is, it's not Lisp that sucks, but Common Lisp.
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