Re: Learning Lisp in Linux?

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.