1 files changed, 117 insertions, 0 deletions
diff --git a/ice-9/poe.scm b/ice-9/poe.scm
new file mode 100644
index 000000000..b594ebe13
--- /dev/null
+++ b/ice-9/poe.scm
@@ -0,0 +1,117 @@
+;;; installed-scm-file
+
+;;;; 	Copyright (C) 1996 Free Software Foundation, Inc.
+;;;; 
+;;;; This program 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, or (at your option)
+;;;; any later version.
+;;;; 
+;;;; This program 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 this software; see the file COPYING.  If not, write to
+;;;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+;;;; 
+
+
+(define-module  #/ice-9/poe
+  :use-module #/ice-9/hcons)
+
+
+
+
+;;; {Pure Functions}
+;;; 
+;;; A pure function (of some sort) is characterized by two equality
+;;; relations: one on argument lists and one on return values.
+;;; A pure function is one that when applied to equal arguments lists
+;;; yields equal results.
+;;;
+;;; If the equality relationship on return values can be eq?, it may make
+;;; sense to cache values returned by the function.  Choosing the right
+;;; equality relation on arguments is tricky.
+;;;
+
+
+;;; {pure-funcq}
+;;;
+;;; The simplest case of pure functions are those in which results
+;;; are only certainly eq? if all of the arguments are.  These functions
+;;; are called "pure-funcq", for obvious reasons.
+;;;
+
+
+(define funcq-memo (make-weak-hash-table 523)) ; !!! randomly selected values
+(define funcq-buffer (make-gc-buffer 256))
+
+(define (funcq-hash arg-list n)
+  (let ((it (let loop ((x 0)
+		       (arg-list arg-list))
+	      (if (null? arg-list)
+		  (modulo x n)
+		  (loop (logior x (hashq (car arg-list) 4194303))
+			(cdr arg-list))))))
+    it))
+
+(define (funcq-assoc arg-list alist)
+  (let ((it (and alist
+		 (let and-map ((key arg-list)
+			       (entry (caar alist)))
+		   (or (and (and (not key) (not entry))
+			    (car alist))
+		       (and key entry
+			    (eq? (car key) (car entry))
+			    (and-map (cdr key) (cdr entry))))))))
+    it))
+
+
+
+(define-public (pure-funcq base-func)
+  (lambda args
+    (let ((cached (hashx-get-handle funcq-hash funcq-assoc funcq-memo (cons base-func args))))
+      (if cached
+	  (begin
+	    (funcq-buffer (car cached))
+	    (cdr cached))
+	    
+	  (let ((val (apply base-func args))
+		(key (cons base-func args)))
+	    (funcq-buffer key)
+	    (hashx-set! funcq-hash funcq-assoc funcq-memo key val)
+	    val)))))
+
+
+
+;;; {Perfect funq}
+;;;
+;;; A pure funq may sometimes forget its past but a perfect
+;;; funcq never does.
+;;;
+
+(define-public (perfect-funcq size base-func)
+  (define funcq-memo (make-hash-table size))
+
+  (lambda args
+    (let ((cached (hashx-get-handle funcq-hash funcq-assoc funcq-memo (cons base-func args))))
+      (if cached
+	  (begin
+	    (funcq-buffer (car cached))
+	    (cdr cached))
+	    
+	  (let ((val (apply base-func args))
+		(key (cons base-func args)))
+	    (funcq-buffer key)
+	    (hashx-set! funcq-hash funcq-assoc funcq-memo key val)
+	    val)))))
+
+
+
+
+
+
+
+