(Nils' Scheme Snippets)

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(intersection . list) => list

Purpose

Compute the intersection of a number of sets.

Arguments

a*	sets

Dependencies

fold-left

Example

(intersection '(v w x) '(w x y) '(x y z)) => (x)

(load "fold-left.scm")

(define (intersection . a*)
  (letrec
    ((intersection2
       (lambda (a b)
         (cond
           ((null? a) '())
           ((member (car a) b)
             (cons (car a) (intersection2 (cdr a) b)))
           (else (intersection2 (cdr a) b))))))
    (cond ((null? a*) '())
      (else (fold-left intersection2 (car a*) (cdr a*))))))