Terminology, neither exact nor complete: Python Lisp APL Perl Haskell map mapcar ? map map filter remove-if-not ? grep filter reduce reduce reduce ? foldl
(This table was made with tablify from http://lists.canonical.org/pipermail/kragen-hacks/2000-September/000263.html and M-h C-u M-| tablify RET in Emacs) I was arguing that 'reduce' was in fact very general, in that any computable function whose domain was an ordered list of things could be expressed in terms of 'reduce', with special ease if the function didn't care about the position of items within the list. It follows that 'map' and 'filter' should be easily expressible in terms of 'reduce', and it turns out they are. Python's 'reduce' works from left to right, like Haskell's foldl. class mapper: def __init__(self, func): self.func = func def __call__(self, list, item): return list + [self.func(item)] squares = reduce(mapper(lambda x: x * x), range(10), []) class filterer: def __init__(self, func): self.func = func def __call__(self, list, item): if self.func(item): return list + [item] else: return list threes = reduce(filterer(lambda x: x % 3 == 0), range(20), []) Here's a Common Lisp version of the same that works from right to left: (defun mapper (fn) (lambda (item list) (cons (funcall fn item) list))) (reduce (mapper (lambda (x) (* x x))) '(1 2 3 4 5 6 7 8 9 10) :from-end t :initial-value '()) (defun filterer (fn) (lambda (item list) (if (funcall fn item) (cons item list) list))) (reduce (filterer (lambda (x) (zerop (mod x 3)))) '(1 2 3 4 5 6 7 8 9 10) :from-end t :initial-value '()) -- /* By Kragen Sitaker, http://pobox.com/~kragen/puzzle2.html */ char a[99]=" KJ",d[999][16];main(){int s=socket(2,1,0),n=0,z,l,i;*(short*)a=2; if(!bind(s,a,16))for(;;){z=16;if((l=recvfrom(s,a,99,0,d[n],&z))>0){for(i=0;i<n; i++){z=(memcmp(d[i],d[n],8))?z:0;while(sendto(s,a,l,0,d[i],16)&0);}z?n++:0;}}}
