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112 lines
2.9 KiB
Scheme
112 lines
2.9 KiB
Scheme
27 years ago
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;; library-set.ss
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; ----------------------------------------------------------------------
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; Copyright (C) 1995-97 Cormac Flanagan
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;
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; This program is free software; you can redistribute it and/or
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; modify it under the terms of the GNU General Public License
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; version 2 as published by the Free Software Foundation.
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;
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; This program is distributed in the hope that it will be useful,
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; but WITHOUT ANY WARRANTY; without even the implied warranty of
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; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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; GNU General Public License for more details.
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;
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; You should have received a copy of the GNU General Public License
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; along with this program; if not, write to the Free Software
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; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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; ----------------------------------------------------------------------
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;;
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;; Set operations implemented by lists.
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;; Identity of elements is based on eq?.
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;; These should probably be sped up some day.
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;; ----------------------------------------------------------------------
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(define empty-set '())
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(define empty-set? null?)
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;; construct a set
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(define set
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(lambda l
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(list->set l)))
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;; construct a set from a list by removing duplicates
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(define list->set
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(match-lambda
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[() '()]
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[(x . y) (if (memq x y)
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(list->set y)
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(cons x (list->set y)))]))
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(define list->set-equal?
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(match-lambda
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[() '()]
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[(x . y) (if (member x y)
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(list->set y)
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(cons x (list->set y)))]))
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;; test for membership
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(define element-of?
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(lambda (x set)
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(and (memq x set) #t)))
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(define (set-add x set)
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(if (memq x set) set (cons x set)))
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(define cardinality length)
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;; does s2 contain s1?
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(define set<=
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(lambda (a b)
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(and (andmap (lambda (x) (memq x b)) a) #t)))
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;; are two sets equal? (mutually containing)
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(define set-eq?
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(lambda (a b)
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(and (= (cardinality a) (cardinality b)) (set<= a b))))
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;; unite two sets
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(define union2
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(lambda (a b)
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(if (null? b)
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a
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(foldr (lambda (x b)
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(if (memq x b)
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b
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(cons x b)))
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b
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a))))
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;; unite any number of sets
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(define union
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(lambda l
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(foldr union2 '() l)))
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(define setdiff2
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(lambda (a b)
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(if (or (null? a) (null? b))
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a
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(if (memq (car a) b)
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(setdiff2 (cdr a) b)
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(cons (car a) (setdiff2 (cdr a) b))))))
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(define setdiff
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(lambda l
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(if (null? l)
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'()
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(setdiff2 (car l) (foldr union2 '() (cdr l))))))
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(define intersect2
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(lambda (a b)
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(cond [(or (null? a) (null? b)) '()]
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[(memq (car b) a) (cons (car b) (intersect2 a (cdr b)))]
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[else (intersect2 a (cdr b))])))
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(define intersect
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(lambda l
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(if (null? l)
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'()
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(foldl intersect2 (car l) l))))
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