(provide 'ucons1)
;; (c) 1990, 1991, Richard J. Fateman
(in-package :mma)
;; alternative to ucons1 file
;; for non-Allegro CL. This is a much inferior version in
;; efficiency of the unique-ification, and any CL could do
;; better. But maybe not the same way.
;;Simplest way to make the substitution would be to rename this
;; file ucons1.lisp.
(defvar *uniq-table* (make-hash-table :test #'eq))
(defvar *uniq-atom-table* (make-hash-table :test #'equal))
(defun uniq (x)
"Return a canonical representation that is EQUAL to x,
such that (equal x y) => (eq (uniq x) (uniq y))"
(typecase x
((or fixnum symbol) x)
(atom (or (gethash x *uniq-atom-table*)
(setf (gethash x *uniq-atom-table*) x)))
(cons (ucons (uniq (car x)) ; this could check in
; *uniq-table* first...
(uniq (cdr x))))))
(defun ucons (x y)
"Unique cons: (eq (ucons x y) (ucons x y)) is always true."
;; Look up the car, x, in the hash-table *uniq-table*.
;; If there a table there, then we have already hashed an
;; item with this car in the table.
;; If it is missing, create a hash-table for the purpose of
;; storing the new (cons x y) in the next step.
(let ((car-table (or (gethash x *uniq-table*)
(setf (gethash x *uniq-table*)
(make-hash-table :test #'eq :size 10)))))
;; At this point, car-table is a hash-table that either has
;; (cons x y) in it, hashed under the key y, or we create
;; such an item and store it.
(or (gethash y car-table)
(setf (gethash y car-table) (cons x y)))))
(defun umapcar(f x)(cond((null x)nil)
(t (ucons (funcall f (car x))(umapcar f (cdr x))))))
(defmacro ulist(&rest l)(cond ((null l)nil)
(t `(ucons ,(car l) (ulist ,@(cdr l))))))
(defun uappend(r s)(cond ((null r)s)
(t (ucons (car r)(uappend (cdr r) s)))))