More dicking around. Stack friendly map.

(define (map func lst)
(if (null? lst) lst
(let ((newlis (list (func (first lst)))))
(let loop ((cur newlis) (lst (rest lst)))
(if (null? lst) newlis
(begin (set-cdr! cur (list (func (first lst))))
(loop (rest cur) (rest lst))))))))

Was trying to implement map with left fold. Wound up with this. The right fold implemention easily blows the stack in guile 1.8. Scheme48 copes perfectly well… with no perceptible difference in speed (which was basically instant) even with a 20k element list. Nice.

This works in both, though. I still have an hour to kill… hmm.


July 31, 2010 - Posted by | Programming, Scheme

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