(Nils' Scheme Snippets)

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(filter proc¹ list) => list

Purpose

Extract elements from a list. The predicate p describes the property of the elements to be extracted.

Arguments

p	predicate
a	source list

Example

(filter number? '(a 1 b 2 c 3)) => (1 2 3)

(define (filter p a)
  (letrec
    ((filter2
       (lambda (a r)
         (cond
           ((null? a) r)
           ((p (car a)) (filter2 (cdr a) (cons (car a) r)))
           (else (filter2 (cdr a) r))))))
    (filter2 (reverse a) '())))

(Nils' Scheme Snippets)

(filter proc1 list) => list

(filter proc¹ list) => list