--- /dev/null
+#| -*-Scheme-*-
+
+Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
+ 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
+ 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016,
+ 2017 Massachusetts Institute of Technology
+
+This file is part of MIT/GNU Scheme.
+
+MIT/GNU Scheme is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or (at
+your option) any later version.
+
+MIT/GNU Scheme is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with MIT/GNU Scheme; if not, write to the Free Software
+Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301,
+USA.
+
+|#
+
+;;;; Predicates: dispatch
+;;; package: (runtime predicate-dispatch)
+
+(declare (usual-integrations))
+\f
+(define predicate-dispatcher?)
+(define maybe-get-metadata)
+(define set-metadata!)
+(define delete-metadata!)
+(add-boot-init!
+ (lambda ()
+ (let ((table (make-hashed-metadata-table)))
+ (set! predicate-dispatcher? (table 'has?))
+ (set! maybe-get-metadata (table 'get-if-available))
+ (set! set-metadata! (table 'put!))
+ (set! delete-metadata! (table 'delete!)))
+ (register-predicate! predicate-dispatcher? 'predicate-dispatcher
+ '<= procedure?)))
+
+(define (get-metadata procedure caller)
+ (let ((metadata (maybe-get-metadata procedure #f)))
+ (if (not metadata)
+ (error:not-a predicate-dispatcher? procedure caller))
+ metadata))
+
+(define (make-predicate-dispatcher name arity make-handler-set)
+ (if (not (> (procedure-arity-min arity) 0))
+ (error:bad-range-argument arity 'make-predicate-dispatcher))
+ (let* ((metadata
+ (make-metadata name
+ arity
+ (make-handler-set (make-default-handler name))))
+ (procedure (make-procedure arity metadata)))
+ (set-metadata! procedure metadata)
+ procedure))
+
+(define (make-default-handler name)
+ (lambda args
+ (error "Inapplicable generic procedure:" name args)))
+
+(define (make-procedure arity metadata)
+ (let ((get-handler ((metadata-handler-set metadata) 'get-handler)))
+ (case (and (eqv? (procedure-arity-min arity) (procedure-arity-max arity))
+ (procedure-arity-min arity))
+ ((1)
+ (lambda (arg)
+ ((get-handler (list arg)) arg)))
+ ((2)
+ (lambda (arg1 arg2)
+ ((get-handler (list arg1 arg2)) arg1 arg2)))
+ ((3)
+ (lambda (arg1 arg2 arg3)
+ ((get-handler (list arg1 arg2 arg3)) arg1 arg2 arg3)))
+ ((4)
+ (lambda (arg1 arg2 arg3 arg4)
+ ((get-handler (list arg1 arg2 arg3 arg4)) arg1 arg2 arg3 arg4)))
+ (else
+ (lambda args
+ (apply (get-handler args) args))))))
+
+(define (simple-predicate-dispatcher name arity)
+ (make-predicate-dispatcher name arity simple-handler-set))
+
+(define (standard-predicate-dispatcher name arity)
+ (make-predicate-dispatcher name arity cached-most-specific-handler-set))
+
+(define (chaining-predicate-dispatcher name arity)
+ (make-predicate-dispatcher name arity cached-chaining-handler-set))
+\f
+(define-record-type <metadata>
+ (make-metadata name arity handler-set)
+ metadata?
+ (name metadata-name)
+ (arity metadata-arity)
+ (handler-set metadata-handler-set))
+
+(define (predicate-dispatcher-name dispatch)
+ (metadata-name (get-metadata dispatch 'predicate-dispatcher-name)))
+
+(define (predicate-dispatcher-arity dispatch)
+ (metadata-arity (get-metadata dispatch 'predicate-dispatcher-arity)))
+
+(define (predicate-dispatcher-rules dispatch)
+ (map list-copy
+ ((get-handler-set dispatch 'predicate-dispatcher-rules) 'get-rules)))
+
+(define (get-handler-set dispatch caller)
+ (metadata-handler-set (get-metadata dispatch caller)))
+
+(define (define-predicate-dispatch-handler dispatch predicates handler)
+ (let ((metadata (get-metadata dispatch 'define-predicate-dispatch-handler)))
+ (guarantee-list-of unary-procedure? predicates
+ 'define-predicate-dispatch-handler)
+ (guarantee-procedure-of-arity handler (metadata-arity metadata)
+ 'define-predicate-dispatch-handler)
+ ((metadata-handler-set metadata) 'set-handler! predicates handler)))
+
+(define (define-predicate-dispatch-default-handler dispatch handler)
+ ((get-handler-set dispatch 'define-predicate-dispatch-default-handler)
+ 'set-default-handler! handler))
+\f
+;;;; Handler set implementations
+
+(define (simple-handler-set default-handler)
+ (let ((rules '()))
+
+ (define (get-handler args)
+ (let loop ((rules rules))
+ (if (pair? rules)
+ (if (predicates-match? (cdar rules) args)
+ (caar rules)
+ (loop (cdr rules)))
+ default-handler)))
+
+ (define (set-handler! predicates handler)
+ (let ((rule
+ (find (lambda (rule)
+ (equal? (cdr rule) predicates))
+ rules)))
+ (if rule
+ (let ((handler* (car rule)))
+ (if handler
+ (set-car! rule handler)
+ (set! rules (delq rule rules)))
+ handler*)
+ (begin
+ (if handler
+ (set! rules
+ (cons (cons handler predicates)
+ rules)))
+ #f))))
+
+ (define (get-default-handler)
+ default-handler)
+
+ (define (set-default-handler! handler)
+ (set! default-handler handler)
+ unspecific)
+
+ (lambda (operator)
+ (case operator
+ ((get-handler) get-handler)
+ ((set-handler!) set-handler!)
+ ((get-default-handler) get-default-handler)
+ ((set-default-handler!) set-default-handler!)
+ ((get-rules) (lambda () rules))
+ (else (error "Unknown operator:" operator))))))
+
+(define (predicates-match? predicates args)
+ (let loop ((predicates predicates) (args args))
+ (or (not (pair? predicates))
+ (and ((car predicates) (car args))
+ (loop (cdr predicates) (cdr args))))))
+\f
+(define (make-subsetting-handler-set make-effective-handler)
+ (lambda (default-handler)
+ (let* ((delegate (simple-handler-set default-handler))
+ (delegate-get-rules (delegate 'get-rules))
+ (delegate-get-default-handler (delegate 'get-default-handler)))
+
+ (define (get-handler args)
+ (let ((matching
+ (let loop ((rules (delegate-get-rules)) (matching '()))
+ (if (pair? rules)
+ (loop (cdr rules)
+ (if (predicates-match? (cdar rules) args)
+ (cons (car rules) matching)
+ matching))
+ matching))))
+ (if (pair? matching)
+ (make-effective-handler (map car (sort matching rule<?))
+ delegate-get-default-handler)
+ (delegate-get-default-handler))))
+
+ (lambda (operator)
+ (case operator
+ ((get-handler) get-handler)
+ (else (delegate operator)))))))
+
+(define (rule<? r1 r2)
+ (let loop ((ps1 (cdr r1)) (ps2 (cdr r2)))
+ (and (pair? ps1)
+ (cond ((eqv? (car ps1) (car ps2)) (loop (cdr ps1) (cdr ps2)))
+ ((predicate<= (car ps1) (car ps2)) #t)
+ ((predicate<= (car ps2) (car ps1)) #f)
+ (else (loop (cdr ps1) (cdr ps2)))))))
+
+(define most-specific-handler-set
+ (make-subsetting-handler-set
+ (lambda (handlers get-default-handler)
+ get-default-handler
+ (car handlers))))
+
+(define chaining-handler-set
+ (make-subsetting-handler-set
+ (lambda (handlers get-default-handler)
+ (let loop ((handlers handlers))
+ (if (pair? handlers)
+ (lambda args
+ (apply (car handlers)
+ (loop (cdr handlers))
+ args))
+ (get-default-handler))))))
+\f
+(define (cached-handler-set delegate get-key)
+ (let ((get-handler
+ (all-args-memoizer eqv?
+ (lambda (args) (map get-key args))
+ (delegate 'get-handler)))
+ (delegate-set-handler! (delegate 'set-handler!))
+ (delegate-set-default-handler! (delegate 'set-default-handler!)))
+
+ (define (set-handler! predicates handler)
+ (clear-memoizer! get-handler)
+ (delegate-set-handler! predicates handler))
+
+ (define (set-default-handler! handler)
+ (clear-memoizer! get-handler)
+ (delegate-set-default-handler! handler))
+
+ (lambda (operator)
+ (case operator
+ ((get-handler) get-handler)
+ ((set-handler!) set-handler!)
+ ((set-default-handler!) set-default-handler!)
+ (else (delegate operator))))))
+
+(define (cached-most-specific-handler-set)
+ (make-cached-handler-set (most-specific-handler-set) object->tag))
+
+(define (cached-chaining-handler-set)
+ (make-cached-handler-set (chaining-handler-set) object->tag))
\ No newline at end of file
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