XPost: comp.lang.scheme

Pascal Costanza wrote:

What about dealing with an arbitrary number of filters?

(defmacro predicate-collect (list &body predicates)
(let ((collectors (mapcar (lambda (predicate)
(declare (ignore predicate))
(gensym "COLLECT"))
predicates))
(collect-t (gensym "COLLECT")))
`(with-collectors (,@collectors ,collect-t)
(dolist (l ,list)
(cond ,@(mapcar (lambda (predicate collector)
`((funcall ,predicate l) (,collector l)))
predicates collectors)
(t (,collect-t l)))))))

An example:

(predicate-collect '(-5 -4 -3 -2 -1 0 1 2 3 4 5)

(function evenp)
(lambda (n) (< n 0))
(lambda (n) (> n 3)))
(-4 -2 0 2 4)
(-5 -3 -1)
(5)
(1 3)

I use the list collector macros by Tim Bradshaw here - see http://www.tfeb.org/lisp/hax.html#COLLECTING

Gauche Scheme

(define (multi-partition the-list . predicates)
(if (null? predicates)
(list the-list)
(receive (yes no)
(partition (car predicates) the-list)
(cons yes (apply multi-partition no (cdr predicates))))))

(multi-partition '(-5 -4 -3 -2 -1 0 1 2 3 4 5)
even?
(is < 0)
(is > 3))

((-4 -2 0 2 4) (-5 -3 -1) (5) (1 3))

Given:

(define-syntax is
(syntax-rules ()
[(is x)
(lambda (y) (equal? y x))]
[(is compare x)
(lambda (y) (compare y x))]
[(is key compare x)
(lambda (y) (compare (key y) x))]))

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Paul Rubin wrote:

Scheme
(define vector-fill!
(lambda (v x)
(let ((n (vector-length v)))
(do ((i 0 (+ i 1)))
((= i n))
(vector-set! v i x)))))

I think you could write the scheme code like this:

(define vector-fill! (v x)
(let ((i 0))
(while (< i (length v))
(vector-set! v i x)
(set! i (1+ i)))))

Gauche Scheme

(define myvec (vector 0 0 0 0 0))
(vector-fill! myvec 99)

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