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;;; isomorph.scm - check isomorphism
;;;
;;; Copyright (c) 2000-2016 Shiro Kawai <shiro@acm.org>
;;;
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;;; modification, are permitted provided that the following conditions
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;;; notice, this list of conditions and the following disclaimer.
;;;
;;; 2. Redistributions in binary form must reproduce the above copyright
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;;; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
;;; "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
;;; LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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;;;
(define-module util.isomorph
(use srfi-1)
(use srfi-43)
(export isomorphic? object-isomorphic?)
)
(select-module util.isomorph)
(define (isomorphic? a b :optional (ctx (make-hash-table)))
(define (iso? a b)
(cond [(or (boolean? a) (null? a) (char? a) (number? a) (symbol? a)
(keyword? a) (undefined? a) (eof-object? a))
(eqv? a b)]
[(hash-table-get ctx a #f) ;node has been appeared
=> (^[bb] (eq? bb b))]
[else
(hash-table-put! ctx a b)
(cond [(pair? a) (and (pair? b)
(iso? (car a) (car b))
(iso? (cdr a) (cdr b)))]
[(string? a) (and (string? b) (string=? a b))]
[(vector? a) (vector-iso? a b)]
[else (object-isomorphic? a b ctx)])]))
(define (vector-iso? a b)
(and (vector? b)
(= (vector-length a) (vector-length b))
(vector-every iso? a b)))
(define (hash-iso? a b)
(and (hash-table? b)
(let loop ([la (hash-table-map a cons)]
[lb (hash-table-map b cons)])
(cond [(null? a) (null? b)]
[(null? b) #f]
[(assq (caar la) lb)
=> (^p (and (iso? (cdar la) (cdr p))
(loop (cdr la) (alist-delete (caar la) lb))))]
[else #f]))))
(unless (hash-table? ctx)
(error "hash table required, but got" ctx))
(iso? a b))
(define-method object-isomorphic? (a b context)
(equal? a b)) ;default
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