;;;;  -*- Mode: Lisp; Syntax: Common-Lisp; Package: SYSTEM -*-
;;;;
;;;   -*- Mode: LISP; Syntax: Common-lisp; Base: 10; Lowercase:T -*-
;;;>
;;;> Portions of LOOP are Copyright (c) 1986 by the Massachusetts Institute of Technology.
;;;> All Rights Reserved.
;;;> 
;;;> Permission to use, copy, modify and distribute this software and its
;;;> documentation for any purpose and without fee is hereby granted,
;;;> provided that the M.I.T. copyright notice appear in all copies and that
;;;> both that copyright notice and this permission notice appear in
;;;> supporting documentation.  The names "M.I.T." and "Massachusetts
;;;> Institute of Technology" may not be used in advertising or publicity
;;;> pertaining to distribution of the software without specific, written
;;;> prior permission.  Notice must be given in supporting documentation that
;;;> copying distribution is by permission of M.I.T.  M.I.T. makes no
;;;> representations about the suitability of this software for any purpose.
;;;> It is provided "as is" without express or implied warranty.
;;;> 
;;;>      Massachusetts Institute of Technology
;;;>      77 Massachusetts Avenue
;;;>      Cambridge, Massachusetts  02139
;;;>      United States of America
;;;>      +1-617-253-1000
;;;>
;;;> Portions of LOOP are Copyright (c) 1989, 1990, 1991, 1992 by Symbolics, Inc.
;;;> All Rights Reserved.
;;;> 
;;;> Permission to use, copy, modify and distribute this software and its
;;;> documentation for any purpose and without fee is hereby granted,
;;;> provided that the Symbolics copyright notice appear in all copies and
;;;> that both that copyright notice and this permission notice appear in
;;;> supporting documentation.  The name "Symbolics" may not be used in
;;;> advertising or publicity pertaining to distribution of the software
;;;> without specific, written prior permission.  Notice must be given in
;;;> supporting documentation that copying distribution is by permission of
;;;> Symbolics.  Symbolics makes no representations about the suitability of
;;;> this software for any purpose.  It is provided "as is" without express
;;;> or implied warranty.
;;;> 
;;;> Symbolics, CLOE Runtime, and Minima are trademarks, and CLOE, Genera,
;;;> and Zetalisp are registered trademarks of Symbolics, Inc.
;;;>
;;;>      Symbolics, Inc.
;;;>      8 New England Executive Park, East
;;;>      Burlington, Massachusetts  01803
;;;>      United States of America
;;;>      +1-617-221-1000

;; $aclHeader: loop.cl,v 1.5 91/12/04 01:13:48 cox acl4_1 $

#+cmu
(ext:file-comment
 "$Header$")

;;;; LOOP Iteration Macro

#+allegro
(in-package :excl)
#+mkcl
(in-package "SI")

#-(or allegro mkcl)
(in-package :ansi-loop)

#-mkcl
(provide :loop)

#+Cloe-Runtime					;Don't ask.
(car (push "%Z% %M% %I% %E% %U%" system::*module-identifications*))

;;; Technology.
;;;
;;; The LOOP iteration macro is one of a number of pieces of code
;;; originally developed at MIT for which free distribution has been
;;; permitted, as long as the code is not sold for profit, and as long
;;; as notification of MIT's interest in the code is preserved.
;;;
;;; This version of LOOP, which is almost entirely rewritten both as
;;; clean-up and to conform with the ANSI Lisp LOOP standard, started
;;; life as MIT LOOP version 829 (which was a part of NIL, possibly
;;; never released).
;;;
;;; A "light revision" was performed by me (Glenn Burke) while at
;;; Palladian Software in April 1986, to make the code run in Common
;;; Lisp.  This revision was informally distributed to a number of
;;; people, and was sort of the "MIT" version of LOOP for running in
;;; Common Lisp.
;;;
;;; A later more drastic revision was performed at Palladian perhaps a
;;; year later.  This version was more thoroughly Common Lisp in style,
;;; with a few miscellaneous internal improvements and extensions.  I
;;; have lost track of this source, apparently never having moved it to
;;; the MIT distribution point.  I do not remember if it was ever
;;; distributed.
;;;
;;; This revision for the ANSI standard is based on the code of my April
;;; 1986 version, with almost everything redesigned and/or rewritten.


;;; The design of this LOOP is intended to permit, using mostly the same
;;; kernel of code, up to three different "loop" macros:
;;; 
;;; (1) The unextended, unextensible ANSI standard LOOP;
;;;
;;; (2) A clean "superset" extension of the ANSI LOOP which provides
;;; functionality similar to that of the old LOOP, but "in the style of"
;;; the ANSI LOOP.  For instance, user-definable iteration paths, with a
;;; somewhat cleaned-up interface.
;;;
;;; (3) Extensions provided in another file which can make this LOOP
;;; kernel behave largely compatibly with the Genera-vintage LOOP macro,
;;; with only a small addition of code (instead of two whole, separate,
;;; LOOP macros).
;;;
;;; Each of the above three LOOP variations can coexist in the same LISP
;;; environment.
;;; 


;;;; Miscellaneous Environment Things



;;;The LOOP-Prefer-POP feature makes LOOP generate code which "prefers" to use POP or
;;; its obvious expansion (prog1 (car x) (setq x (cdr x))).  Usually this involves
;;; shifting fenceposts in an iteration or series of carcdr operations.  This is
;;; primarily recognized in the list iterators (FOR .. {IN,ON}), and LOOP's
;;; destructuring setq code.
(eval-when (compile load eval)
  #+(or Genera Minima) (pushnew :LOOP-Prefer-POP *features*)
  )


;;; The uses of this macro are retained in the CL version of loop, in
;;; case they are needed in a particular implementation.  Originally
;;; dating from the use of the Zetalisp COPYLIST* function, this is used
;;; in situations where, were cdr-coding in use, having cdr-NIL at the
;;; end of the list might be suboptimal because the end of the list will
;;; probably be RPLACDed and so cdr-normal should be used instead.
(defmacro loop-copylist* (l)
  #+Genera `(lisp:copy-list ,l nil t)		; arglist = (list &optional area force-dotted)
  ;;Explorer??
  #-Genera `(copy-list ,l)
  )

(defvar *loop-real-data-type* 'real)

(defun loop-optimization-quantities (env)
  ;; The ANSI conditionalization here is for those lisps that implement
  ;; DECLARATION-INFORMATION (from cleanup SYNTACTIC-ENVIRONMENT-ACCESS).
  ;; It is really commentary on how this code could be written.  I don't
  ;; actually expect there to be an ANSI #+-conditional -- it should be
  ;; replaced with the appropriate conditional name for your
  ;; implementation/dialect.
  (declare #-ANSI (ignore env)
	   #+Genera (values speed space safety compilation-speed debug))
  #+ANSI (let ((stuff (declaration-information 'optimize env)))
	   (values (or (cdr (assoc 'speed stuff)) 1)
		   (or (cdr (assoc 'space stuff)) 1)
		   (or (cdr (assoc 'safety stuff)) 1)
		   (or (cdr (assoc 'compilation-speed stuff)) 1)
		   (or (cdr (assoc 'debug stuff)) 1)))
  #+CLOE-Runtime (values compiler::time compiler::space
			 compiler::safety compiler::compilation-speed 1)
  #-(or ANSI CLOE-Runtime) (values 1 1 1 1 1))


;;; The following form takes a list of variables and a form which presumably
;;; references those variables, and wraps it somehow so that the compiler does not
;;; consider those variables have been referenced.  The intent of this is that
;;; iteration variables can be flagged as unused by the compiler, e.g. I in
;;; (loop for i from 1 to 10 do (print t)), since we will tell it when a usage
;;; of it is "invisible" or "not to be considered".
;;;We implicitly assume that a setq does not count as a reference.  That is, the
;;; kind of form generated for the above loop construct to step I, simplified, is
;;; `(SETQ I ,(HIDE-VARIABLE-REFERENCES '(I) '(1+ I))).
(defun hide-variable-references (variable-list form)
  (declare #-Genera (ignore variable-list))
  #+Genera (if variable-list `(compiler:invisible-references ,variable-list ,form) form)
  #-Genera form)


;;; The following function takes a flag, a variable, and a form which presumably
;;; references that variable, and wraps it somehow so that the compiler does not
;;; consider that variable to have been referenced.  The intent of this is that
;;; iteration variables can be flagged as unused by the compiler, e.g. I in
;;; (loop for i from 1 to 10 do (print t)), since we will tell it when a usage
;;; of it is "invisible" or "not to be considered".
;;;We implicitly assume that a setq does not count as a reference.  That is, the
;;; kind of form generated for the above loop construct to step I, simplified, is
;;; `(SETQ I ,(HIDE-VARIABLE-REFERENCES T 'I '(1+ I))).
;;;Certain cases require that the "invisibility" of the reference be conditional upon
;;; something.  This occurs in cases of "named" variables (the USING clause).  For instance,
;;; we want IDX in (LOOP FOR E BEING THE VECTOR-ELEMENTS OF V USING (INDEX IDX) ...)
;;; to be "invisible" when it is stepped, so that the user gets informed if IDX is
;;; not referenced.  However, if no USING clause is present, we definitely do not
;;; want to be informed that some random gensym is not used.
;;;It is easier for the caller to do this conditionally by passing a flag (which
;;; happens to be the second value of NAMED-VARIABLE, q.v.) to this function than
;;; for all callers to contain the conditional invisibility construction.
(defun hide-variable-reference (really-hide variable form)
  (declare #-Genera (ignore really-hide variable))
  #+Genera (if (and really-hide variable (atom variable))	;Punt on destructuring patterns
	       `(compiler:invisible-references (,variable) ,form)
	       form)
  #-Genera form)


;;;; List Collection Macrology


(defmacro with-loop-list-collection-head ((head-var tail-var &optional user-head-var)
					  &body body)
  ;; TI? Exploder?
  #+LISPM (let ((head-place (or user-head-var head-var)))
	    `(let* ((,head-place nil)
		    (,tail-var
		      ,(hide-variable-reference
			 user-head-var user-head-var
			 `(progn #+Genera (scl:locf ,head-place)
				 #-Genera (system:variable-location ,head-place)))))
	       ,@body))
  #-LISPM (let ((l (and user-head-var (list (list user-head-var nil)))))
	    #+CLOE `(sys::with-stack-list* (,head-var nil nil)
		      (let ((,tail-var ,head-var) ,@l)
			,@body))
	    #-CLOE `(let* ((,head-var (list nil)) (,tail-var ,head-var) ,@l)
		      ,@body)))


(defmacro loop-collect-rplacd (&environment env
			       (head-var tail-var &optional user-head-var) form)
  (declare
    #+LISPM (ignore head-var user-head-var)	;use locatives, unconditionally update through the tail.
    )
  (setq form (macroexpand form env))
  (flet ((cdr-wrap (form n)
	   (declare (fixnum n))
	   (do () ((<= n 4) (setq form `(,(case n
					    (1 'cdr)
					    (2 'cddr)
					    (3 'cdddr)
					    (4 'cddddr))
					 ,form)))
	     (setq form `(cddddr ,form) n (- n 4)))))
    (let ((tail-form form) (ncdrs nil))
      ;;Determine if the form being constructed is a list of known length.
      (when (consp form)
	(cond ((eq (car form) 'list)
	       (setq ncdrs (1- (length (cdr form))))
	       ;; Because the last element is going to be RPLACDed,
	       ;; we don't want the cdr-coded implementations to use
	       ;; cdr-nil at the end (which would just force copying
	       ;; the whole list again).
	       #+LISPM (setq tail-form `(list* ,@(cdr form) nil)))
	      ((member (car form) '(list* cons))
	       (when (and (cddr form) (member (car (last form)) '(nil 'nil)))
		 (setq ncdrs (- (length (cdr form)) 2))))))
      (let ((answer
	      (cond ((null ncdrs)
		     `(when (setf (cdr ,tail-var) ,tail-form)
			(setq ,tail-var (last (cdr ,tail-var)))))
		    ((< ncdrs 0) (return-from loop-collect-rplacd nil))
		    ((= ncdrs 0)
		     ;; Here we have a choice of two idioms:
		     ;; (rplacd tail (setq tail tail-form))
		     ;; (setq tail (setf (cdr tail) tail-form)).
		     ;;Genera and most others I have seen do better with the former.
		     `(rplacd ,tail-var (setq ,tail-var ,tail-form)))
		    (t `(setq ,tail-var ,(cdr-wrap `(setf (cdr ,tail-var) ,tail-form)
						   ncdrs))))))
	;;If not using locatives or something similar to update the user's
	;; head variable, we've got to set it...  It's harmless to repeatedly set it
	;; unconditionally, and probably faster than checking.
	#-LISPM (when user-head-var
		  (setq answer `(progn ,answer (setq ,user-head-var (cdr ,head-var)))))
	answer))))


(defmacro loop-collect-answer (head-var &optional user-head-var)
  (or user-head-var
      (progn
	;;If we use locatives to get tail-updating to update the head var,
	;; then the head var itself contains the answer.  Otherwise we
	;; have to cdr it.
	#+LISPM head-var
	#-LISPM `(cdr ,head-var))))



;;;; Maximization Technology

#|
The basic idea of all this minimax randomness here is that we have to
have constructed all uses of maximize and minimize to a particular
"destination" before we can decide how to code them.  The goal is to not
have to have any kinds of flags, by knowing both that (1) the type is
something which we can provide an initial minimum or maximum value for
and (2) know that a MAXIMIZE and MINIMIZE are not being combined.

SO, we have a datastructure which we annotate with all sorts of things,
incrementally updating it as we generate loop body code, and then use
a wrapper and internal macros to do the coding when the loop has been
constructed.
|#


(defstruct (loop-minimax
	     #+mkcl (:type vector)
	     (:constructor make-loop-minimax-internal)
	     #+nil (:copier nil)
	     #+nil (:predicate nil))
  answer-variable
  type
  temp-variable
  flag-variable
  operations
  infinity-data)


(defvar *loop-minimax-type-infinities-alist*
	;; This is the sort of value this should take on for a Lisp that has
	;; "eminently usable" infinities.  n.b. there are neither constants nor
	;; printed representations for infinities defined by CL.
	;; This grotesque read-from-string below is to help implementations
	;; which croak on the infinity character when it appears in a token, even
	;; conditionalized out.
; 	#+Genera
; 	  '#.(read-from-string
; 	      "((fixnum 	most-positive-fixnum	 most-negative-fixnum)
; 		(short-float 	+1s			 -1s)
; 		(single-float	+1f			 -1f)
; 		(double-float	+1d			 -1d)
; 		(long-float	+1l			 -1l))")
	;;This is how the alist should look for a lisp that has no infinities.  In
	;; that case, MOST-POSITIVE-x-FLOAT really IS the most positive.
	#+(or CLOE-Runtime Minima)
	  '((fixnum   		most-positive-fixnum		most-negative-fixnum)
	    (short-float	most-positive-short-float	most-negative-short-float)
	    (single-float	most-positive-single-float	most-negative-single-float)
	    (double-float	most-positive-double-float	most-negative-double-float)
	    (long-float		most-positive-long-float	most-negative-long-float))
	;; CMUCL has infinities so let's use them.
	#+CMU
	  '((fixnum		most-positive-fixnum			most-negative-fixnum)
	    (short-float	ext:single-float-positive-infinity	ext:single-float-negative-infinity)
	    (single-float	ext:single-float-positive-infinity	ext:single-float-negative-infinity)
	    (double-float	ext:double-float-positive-infinity	ext:double-float-negative-infinity)
	    (long-float		ext:long-float-positive-infinity	ext:long-float-negative-infinity))
	;; If we don't know, then we cannot provide "infinite" initial values for any of the
	;; types but FIXNUM:
	#-(or Genera CLOE-Runtime Minima CMU)
	  '((fixnum   		most-positive-fixnum		most-negative-fixnum))
	  )


(defun make-loop-minimax (answer-variable type)
  (let ((infinity-data (cdr (assoc type *loop-minimax-type-infinities-alist* :test #'subtypep))))
    (make-loop-minimax-internal
      :answer-variable answer-variable
      :type type
      :temp-variable (gensym "LOOP-MAXMIN-TEMP-")
      :flag-variable (and (not infinity-data) (gensym "LOOP-MAXMIN-FLAG-"))
      :operations nil
      :infinity-data infinity-data)))


(defun loop-note-minimax-operation (operation minimax)
  (pushnew (the symbol operation) (loop-minimax-operations minimax))
  (when (and (cdr (loop-minimax-operations minimax))
	     (not (loop-minimax-flag-variable minimax)))
    (setf (loop-minimax-flag-variable minimax) (gensym "LOOP-MAXMIN-FLAG-")))
  operation)


(defmacro with-minimax-value (lm &body body)
  (let ((init (loop-typed-init (loop-minimax-type lm)))
	(which (car (loop-minimax-operations lm)))
	(infinity-data (loop-minimax-infinity-data lm))
	(answer-var (loop-minimax-answer-variable lm))
	(temp-var (loop-minimax-temp-variable lm))
	(flag-var (loop-minimax-flag-variable lm))
	(type (loop-minimax-type lm)))
    (if flag-var
	`(let ((,answer-var ,init) (,temp-var ,init) (,flag-var nil))
	   (declare (type ,type ,answer-var ,temp-var))
	   ,@body)
	`(let ((,answer-var ,(if (eq which 'min) (first infinity-data) (second infinity-data)))
	       (,temp-var ,init))
	   (declare (type ,type ,answer-var ,temp-var))
	   ,@body))))


(defmacro loop-accumulate-minimax-value (lm operation form)
  (let* ((answer-var (loop-minimax-answer-variable lm))
	 (temp-var (loop-minimax-temp-variable lm))
	 (flag-var (loop-minimax-flag-variable lm))
	 (test
	   (hide-variable-reference
	     t (loop-minimax-answer-variable lm)
	     `(,(ecase operation
		  (min '<)
		  (max '>))
	       ,temp-var ,answer-var))))
    `(progn
       (setq ,temp-var ,form)
       (when ,(if flag-var `(or (not ,flag-var) ,test) test)
	 (setq ,@(and flag-var `(,flag-var t))
	       ,answer-var ,temp-var)))))



;;;; Loop Keyword Tables

#|
LOOP keyword tables are hash tables string keys and a test of EQUAL.

The actual descriptive/dispatch structure used by LOOP is called a "loop
universe" contains a few tables and parameterizations.  The basic idea is
that we can provide a non-extensible ANSI-compatible loop environment,
an extensible ANSI-superset loop environment, and (for such environments
as CLOE) one which is "sufficiently close" to the old Genera-vintage
LOOP for use by old user programs without requiring all of the old LOOP
code to be loaded.
|#


;;;; Token Hackery


;;;Compare two "tokens".  The first is the frob out of *LOOP-SOURCE-CODE*,
;;; the second a symbol to check against.
(defun loop-tequal (x1 x2)
  (and (symbolp x1) (string= x1 x2)))


(defun loop-tassoc (kwd alist)
  (and (symbolp kwd) (assoc kwd alist :test #'string=)))


(defun loop-tmember (kwd list)
  (and (symbolp kwd) (member kwd list :test #'string=)))


(defun loop-lookup-keyword (loop-token table)
  (and (symbolp loop-token)
       (values (gethash (symbol-name loop-token) table))))


(defmacro loop-store-table-data (symbol table datum)
  `(setf (gethash (symbol-name ,symbol) ,table) ,datum))


(defstruct (loop-universe
	     #+mkcl (:type vector)
	     #-mkcl (:print-function print-loop-universe)
	     #+nil (:copier nil)
	     #+nil (:predicate nil))
  keywords					;hash table, value = (fn-name . extra-data).
  iteration-keywords				;hash table, value = (fn-name . extra-data).
  for-keywords					;hash table, value = (fn-name . extra-data).
  path-keywords					;hash table, value = (fn-name . extra-data).
  type-symbols					;hash table of type SYMBOLS, test EQ, value = CL type specifier.
  type-keywords					;hash table of type STRINGS, test EQUAL, value = CL type spec.
  ansi						;NIL, T, or :EXTENDED.
  implicit-for-required				;see loop-hack-iteration
  )


#-mkcl
(defun print-loop-universe (u stream level)
  (declare (ignore level))
  (let ((str (case (loop-universe-ansi u)
	       ((nil) "Non-ANSI")
	       ((t) "ANSI")
	       (:extended "Extended-ANSI")
	       (t (loop-universe-ansi u)))))
    ;;Cloe could be done with the above except for bootstrap lossage...
    #+CLOE
    (format stream "#<~S ~A ~X>" (type-of u) str (sys::address-of u))
    #+Genera					; This is reallly the ANSI definition.
    (print-unreadable-object (u stream :type t :identity t)
      (princ str stream))
    #-(or Genera CLOE)
    (format stream "#<~S ~A>" (type-of u) str)
    ))


;;;This is the "current" loop context in use when we are expanding a
;;;loop.  It gets bound on each invocation of LOOP.
(defvar *loop-universe*)


(defun make-standard-loop-universe (&key keywords for-keywords iteration-keywords path-keywords
				    type-keywords type-symbols ansi)
  #-(and CLOE Source-Bootstrap mkcl) (check-type ansi (member nil t :extended))
  (flet ((maketable (entries)
	   (let* ((size (length entries))
		  (ht (make-hash-table :size (if (< size 10) 10 size) :test #'equal)))
	     (dolist (x entries) (setf (gethash (symbol-name (car x)) ht) (cadr x)))
	     ht)))
    (make-loop-universe
      :keywords (maketable keywords)
      :for-keywords (maketable for-keywords)
      :iteration-keywords (maketable iteration-keywords)
      :path-keywords (maketable path-keywords)
      :ansi ansi
      :implicit-for-required (not (null ansi))
      :type-keywords (maketable type-keywords)
      :type-symbols (let* ((size (length type-symbols))
			   (ht (make-hash-table :size (if (< size 10) 10 size) :test #'eq)))
		      (dolist (x type-symbols)
			(if (atom x) (setf (gethash x ht) x) (setf (gethash (car x) ht) (cadr x))))
		      ht)))) 


;;;; Setq Hackery


(defvar *loop-destructuring-hooks*
	nil
  "If not NIL, this must be a list of two things:
a LET-like macro, and a SETQ-like macro, which perform LOOP-style destructuring.")


(defun loop-make-psetq (frobs)
  (and frobs
       (loop-make-desetq
	 (list (car frobs)
	       (if (null (cddr frobs)) (cadr frobs)
		   `(prog1 ,(cadr frobs)
			   ,(loop-make-psetq (cddr frobs))))))))


(defun loop-make-desetq (var-val-pairs)
  (if (null var-val-pairs)
      nil
      (cons (if *loop-destructuring-hooks*
		(cadr *loop-destructuring-hooks*)
		'loop-really-desetq)
	    var-val-pairs)))


(defvar *loop-desetq-temporary*
	(make-symbol "LOOP-DESETQ-TEMP"))


(defmacro loop-really-desetq (&environment env &rest var-val-pairs)
  (labels ((find-non-null (var)
	     ;; see if there's any non-null thing here
	     ;; recurse if the list element is itself a list
	     (do ((tail var)) ((not (consp tail)) tail)
	       (when (find-non-null (pop tail)) (return t))))
	   (loop-desetq-internal (var val &optional temp)
	     ;; returns a list of actions to be performed
	     (typecase var
	       (null
		 (when (consp val)
		   ;; don't lose possible side-effects
		   (if (eq (car val) 'prog1)
		       ;; these can come from psetq or desetq below.
		       ;; throw away the value, keep the side-effects.
		       ;;Special case is for handling an expanded POP.
		       (mapcan #'(lambda (x)
				   (and (consp x)
					(or (not (eq (car x) 'car))
					    (not (symbolp (cadr x)))
					    (not (symbolp (setq x (macroexpand x env)))))
					(cons x nil)))
			       (cdr val))
		       `(,val))))
	       (cons
		 (let* ((car (car var))
			(cdr (cdr var))
			(car-non-null (find-non-null car))
			(cdr-non-null (find-non-null cdr)))
		   (when (or car-non-null cdr-non-null)
		     (if cdr-non-null
			 (let* ((temp-p temp)
				(temp (or temp *loop-desetq-temporary*))
				(body #+LOOP-Prefer-POP `(,@(loop-desetq-internal
							      car
							      `(prog1 (car ,temp)
								      (setq ,temp (cdr ,temp))))
							  ,@(loop-desetq-internal cdr temp temp))
				      #-LOOP-Prefer-POP `(,@(loop-desetq-internal car `(car ,temp))
							  (setq ,temp (cdr ,temp))
							  ,@(loop-desetq-internal cdr temp temp))))
			   (if temp-p
			       `(,@(unless (eq temp val)
				     `((setq ,temp ,val)))
				 ,@body)
			       `((let ((,temp ,val))
				   ,@body))))
			 ;; no cdring to do
			 (loop-desetq-internal car `(car ,val) temp)))))
	       (otherwise
		 (unless (eq var val)
		   `((setq ,var ,val)))))))
    (do ((actions))
	((null var-val-pairs)
	 (if (null (cdr actions)) (car actions) `(progn ,@(nreverse actions))))
      (setq actions (revappend
		      (loop-desetq-internal (pop var-val-pairs) (pop var-val-pairs))
		      actions)))))


;;;; LOOP-local variables

;;;This is the "current" pointer into the LOOP source code.
(defvar *loop-source-code*)


;;;This is the pointer to the original, for things like NAMED that
;;;insist on being in a particular position
(defvar *loop-original-source-code*)


;;;This is *loop-source-code* as of the "last" clause.  It is used
;;;primarily for generating error messages (see loop-error, loop-warn).
(defvar *loop-source-context*)


;;;List of names for the LOOP, supplied by the NAMED clause.
(defvar *loop-names*)

;;;The macroexpansion environment given to the macro.
(defvar *loop-macro-environment*)

;;;This holds variable names specified with the USING clause.
;;; See LOOP-NAMED-VARIABLE.
(defvar *loop-named-variables*)

;;; LETlist-like list being accumulated for one group of parallel bindings.
(defvar *loop-variables*)

;;;List of declarations being accumulated in parallel with
;;;*loop-variables*.
(defvar *loop-declarations*)

;;;Used by LOOP for destructuring binding, if it is doing that itself.
;;; See loop-make-variable.
(defvar *loop-desetq-crocks*)

;;; List of wrapping forms, innermost first, which go immediately inside
;;; the current set of parallel bindings being accumulated in
;;; *loop-variables*.  The wrappers are appended onto a body.  E.g.,
;;; this list could conceivably has as its value ((with-open-file (g0001
;;; g0002 ...))), with g0002 being one of the bindings in
;;; *loop-variables* (this is why the wrappers go inside of the variable
;;; bindings).
(defvar *loop-wrappers*)

;;;This accumulates lists of previous values of *loop-variables* and the
;;;other lists  above, for each new nesting of bindings.  See
;;;loop-bind-block.
(defvar *loop-bind-stack*)

;;;This is a LOOP-global variable for the (obsolete) NODECLARE clause
;;;which inhibits  LOOP from actually outputting a type declaration for
;;;an iteration (or any) variable.
(defvar *loop-nodeclare*)

;;;This is simply a list of LOOP iteration variables, used for checking
;;;for duplications.
(defvar *loop-iteration-variables*)


;;;List of prologue forms of the loop, accumulated in reverse order.
(defvar *loop-prologue*)

(defvar *loop-before-loop*)
(defvar *loop-body*)
(defvar *loop-after-body*)

;;;This is T if we have emitted any body code, so that iteration driving
;;;clauses can be disallowed.   This is not strictly the same as
;;;checking *loop-body*, because we permit some clauses  such as RETURN
;;;to not be considered "real" body (so as to permit the user to "code"
;;;an  abnormal return value "in loop").
(defvar *loop-emitted-body*)


;;;List of epilogue forms (supplied by FINALLY generally), accumulated
;;; in reverse order.
(defvar *loop-epilogue*)

;;;List of epilogue forms which are supplied after the above "user"
;;;epilogue.  "normal" termination return values are provide by putting
;;;the return form in here.  Normally this is done using
;;;loop-emit-final-value, q.v.
(defvar *loop-after-epilogue*)

;;;The "culprit" responsible for supplying a final value from the loop.
;;;This  is so loop-emit-final-value can moan about multiple return
;;;values being supplied.
(defvar *loop-final-value-culprit*)

;;;If not NIL, we are in some branch of a conditional.  Some clauses may
;;;be disallowed.
(defvar *loop-inside-conditional*)

;;;If not NIL, this is a temporary bound around the loop for holding the
;;;temporary  value for "it" in things like "when (f) collect it".  It
;;;may be used as a supertemporary by some other things.
(defvar *loop-when-it-variable*)

;;;Sometimes we decide we need to fold together parts of the loop, but
;;;some part of the generated iteration  code is different for the first
;;;and remaining iterations.  This variable will be the temporary which 
;;;is the flag used in the loop to tell whether we are in the first or
;;;remaining iterations.
(defvar *loop-never-stepped-variable*)

;;;List of all the value-accumulation descriptor structures in the loop.
;;; See loop-get-collection-info.
(defvar *loop-collection-cruft*)		; for multiple COLLECTs (etc)


;;;; Code Analysis Stuff


(defun loop-constant-fold-if-possible (form &optional expected-type)
  #+Genera (declare (values new-form constantp constant-value))
  (let ((new-form form) (constantp nil) (constant-value nil))
    #+Genera (setq new-form (compiler:optimize-form form *loop-macro-environment*
						    :repeat t
						    :do-macro-expansion t
						    :do-named-constants t
						    :do-inline-forms t
						    :do-optimizers t
						    :do-constant-folding t
						    :do-function-args t)
		   constantp (constantp new-form *loop-macro-environment*)
		   constant-value (and constantp (lt:evaluate-constant new-form *loop-macro-environment*)))
    #-Genera (when (setq constantp (constantp new-form))
	       (setq constant-value (eval new-form)))
    (when (and constantp expected-type)
      (unless (typep constant-value expected-type)
	(loop-warn "The form ~S evaluated to ~S, which was not of the anticipated type ~S."
		   form constant-value expected-type)
	(setq constantp nil constant-value nil)))
    (values new-form constantp constant-value)))


(defun loop-constantp (form)
  #+Genera (constantp form *loop-macro-environment*)
  #-Genera (constantp form))


;;;; LOOP Iteration Optimization

(defvar *loop-duplicate-code*
	nil)


(defvar *loop-iteration-flag-variable*
	(make-symbol "LOOP-NOT-FIRST-TIME"))


(defun loop-code-duplication-threshold (env)
  (multiple-value-bind (speed space) (loop-optimization-quantities env)
    (+ 40 (* (- speed space) 10))))


(defmacro loop-body (&environment env
		     prologue
		     before-loop
		     main-body
		     after-loop
		     epilogue
		     &aux rbefore rafter flagvar)
  (unless (= (length before-loop) (length after-loop))
    (error "LOOP-BODY called with non-synched before- and after-loop lists."))
  ;;All our work is done from these copies, working backwards from the end:
  (setq rbefore (reverse before-loop) rafter (reverse after-loop))
  (labels ((psimp (l)
	     (let ((ans nil))
	       (dolist (x l)
		 (when x
		   (push x ans)
		   (when (and (consp x) (member (car x) '(go return return-from)))
		     (return nil))))
	       (nreverse ans)))
	   (pify (l) (if (null (cdr l)) (car l) `(progn ,@l)))
	   (makebody ()
	     (let ((form `(tagbody
			    ,@(psimp (append prologue (nreverse rbefore)))
			 next-loop
			    ,@(psimp (append main-body (nreconc rafter `((go next-loop)))))
			 end-loop
			    ,@(psimp epilogue))))
	       (if flagvar `(let ((,flagvar nil)) ,form) form))))
    (when (or *loop-duplicate-code* (not rbefore))
      (return-from loop-body (makebody)))
    ;; This outer loop iterates once for each not-first-time flag test generated
    ;; plus once more for the forms that don't need a flag test
    (do ((threshold (loop-code-duplication-threshold env))) (nil)
      (declare (fixnum threshold))
      ;; Go backwards from the ends of before-loop and after-loop merging all the equivalent
      ;; forms into the body.
      (do () ((or (null rbefore) (not (equal (car rbefore) (car rafter)))))
	(push (pop rbefore) main-body)
	(pop rafter))
      (unless rbefore (return (makebody)))
      ;; The first forms in rbefore & rafter (which are the chronologically
      ;; last forms in the list) differ, therefore they cannot be moved
      ;; into the main body.  If everything that chronologically precedes
      ;; them either differs or is equal but is okay to duplicate, we can
      ;; just put all of rbefore in the prologue and all of rafter after
      ;; the body.  Otherwise, there is something that is not okay to
      ;; duplicate, so it and everything chronologically after it in
      ;; rbefore and rafter must go into the body, with a flag test to
      ;; distinguish the first time around the loop from later times.
      ;; What chronologically precedes the non-duplicatable form will
      ;; be handled the next time around the outer loop.
      (do ((bb rbefore (cdr bb)) (aa rafter (cdr aa)) (lastdiff nil) (count 0) (inc nil))
	  ((null bb) (return-from loop-body (makebody)))	;Did it.
	(cond ((not (equal (car bb) (car aa))) (setq lastdiff bb count 0))
	      ((or (not (setq inc (estimate-code-size (car bb) env)))
		   (> (incf count inc) threshold))
	       ;; Ok, we have found a non-duplicatable piece of code.  Everything
	       ;; chronologically after it must be in the central body.
	       ;; Everything chronologically at and after lastdiff goes into the
	       ;; central body under a flag test.
	       (let ((then nil) (else nil))
		 (do () (nil)
		   (push (pop rbefore) else)
		   (push (pop rafter) then)
		   (when (eq rbefore (cdr lastdiff)) (return)))
		 (unless flagvar
		   (push `(setq ,(setq flagvar *loop-iteration-flag-variable*) t) else))
		 (push `(if ,flagvar ,(pify (psimp then)) ,(pify (psimp else)))
		       main-body))
	       ;; Everything chronologically before lastdiff until the non-duplicatable form (car bb) 
	       ;; is the same in rbefore and rafter so just copy it into the body
	       (do () (nil)
		 (pop rafter)
		 (push (pop rbefore) main-body)
		 (when (eq rbefore (cdr bb)) (return)))
	       (return)))))))



(defun duplicatable-code-p (expr env)
  (if (null expr) 0
      (let ((ans (estimate-code-size expr env)))
	(declare (fixnum ans))
	;; Use (DECLARATION-INFORMATION 'OPTIMIZE ENV) here to get an alist of
	;; optimize quantities back to help quantify how much code we are willing to
	;; duplicate.
	ans)))


(defvar *special-code-sizes*
	'((return 0) (progn 0)
	  (null 1) (not 1) (eq 1) (car 1) (cdr 1)
	  (when 1) (unless 1) (if 1)
	  (caar 2) (cadr 2) (cdar 2) (cddr 2)
	  (caaar 3) (caadr 3) (cadar 3) (caddr 3) (cdaar 3) (cdadr 3) (cddar 3) (cdddr 3)
	  (caaaar 4) (caaadr 4) (caadar 4) (caaddr 4)
	  (cadaar 4) (cadadr 4) (caddar 4) (cadddr 4)
	  (cdaaar 4) (cdaadr 4) (cdadar 4) (cdaddr 4)
	  (cddaar 4) (cddadr 4) (cdddar 4) (cddddr 4)))


(defvar *estimate-code-size-punt*
	'(block
	   do do* dolist
	   flet
	   labels lambda let let* locally
	   macrolet multiple-value-bind
	   prog prog*
	   symbol-macrolet
	   tagbody
	   unwind-protect
	   with-open-file))


(defun destructuring-size (x)
  (do ((x x (cdr x)) (n 0 (+ (destructuring-size (car x)) n)))
      ((atom x) (+ n (if (null x) 0 1)))))


(defun estimate-code-size (x env)
  (catch 'estimate-code-size
    (estimate-code-size-1 x env)))


(defun estimate-code-size-1 (x env)
  (flet ((list-size (l)
	   (let ((n 0))
	     (declare (fixnum n))
	     (dolist (x l n) (incf n (estimate-code-size-1 x env))))))
    ;; ???? (declare (function list-size (list) fixnum))
    (cond ((constantp x #+Genera env) 1)
	  ((symbolp x) (multiple-value-bind (new-form expanded-p) (macroexpand-1 x env)
			 (if expanded-p (estimate-code-size-1 new-form env) 1)))
	  ((atom x) 1)				;??? self-evaluating???
	  ((symbolp (car x))
	   (let ((fn (car x)) (tem nil) (n 0))
	     (declare (symbol fn) (fixnum n))
	     (macrolet ((f (overhead &optional (args nil args-p))
			  `(the fixnum (+ (the fixnum ,overhead)
					  (the fixnum (list-size ,(if args-p args '(cdr x))))))))
	       (cond ((setq tem (get-sysprop fn 'estimate-code-size))
		      (typecase tem
			(fixnum (f tem))
			(t (funcall tem x env))))
		     ((setq tem (assoc fn *special-code-sizes*)) (f (second tem)))
		     #+Genera
		     ((eq fn 'compiler:invisible-references) (list-size (cddr x)))
		     ((eq fn 'cond)
		      (dolist (clause (cdr x) n) (incf n (list-size clause)) (incf n)))
		     ((eq fn 'desetq)
		      (do ((l (cdr x) (cdr l))) ((null l) n)
			(setq n (+ n (destructuring-size (car l)) (estimate-code-size-1 (cadr l) env)))))
		     ((member fn '(setq psetq))
		      (do ((l (cdr x) (cdr l))) ((null l) n)
			(setq n (+ n (estimate-code-size-1 (cadr l) env) 1))))
		     ((eq fn 'go) 1)
		     ((eq fn 'function)
		      ;;This skirts the issue of implementationally-defined lambda macros
		      ;; by recognizing CL function names and nothing else.
		      (if (or (symbolp (cadr x))
			      (and (consp (cadr x)) (eq (caadr x) 'setf)))
			  1
			  (throw 'duplicatable-code-p nil)))
		     ((eq fn 'multiple-value-setq) (f (length (second x)) (cddr x)))
		     ((eq fn 'return-from) (1+ (estimate-code-size-1 (third x) env)))
		     ((or (special-operator-p fn) (member fn *estimate-code-size-punt*))
		      (throw 'estimate-code-size nil))
		     (t (multiple-value-bind (new-form expanded-p) (macroexpand-1 x env)
			  (if expanded-p
			      (estimate-code-size-1 new-form env)
			      (f 3))))))))
	  (t (throw 'estimate-code-size nil)))))


;;;; Loop Errors


(defun loop-context ()
  (do ((l *loop-source-context* (cdr l)) (new nil (cons (car l) new)))
      ((eq l (cdr *loop-source-code*)) (nreverse new))))


(defun loop-error (format-string &rest format-args)
  (si::simple-program-error "~?~%Current LOOP context:~{ ~S~}."
			    format-string format-args (loop-context)))


(defun loop-warn (format-string &rest format-args)
  (warn "~?~%Current LOOP context:~{ ~S~}." format-string format-args (loop-context)))


(defun loop-check-data-type (specified-type required-type
			     &optional (default-type required-type))
  (if (null specified-type)
      default-type
      (multiple-value-bind (a b) (subtypep specified-type required-type)
	(cond ((not b)
	       (loop-warn "LOOP couldn't verify that ~S is a subtype of the required type ~S."
			  specified-type required-type))
	      ((not a)
	       (loop-error "Specified data type ~S is not a subtype of ~S."
			   specified-type required-type)))
	specified-type)))


;;;INTERFACE: Traditional, ANSI, Lucid.
(defmacro loop-finish () 
  "Causes the iteration to terminate \"normally\", the same as implicit
termination by an iteration driving clause, or by use of WHILE or
UNTIL -- the epilogue code (if any) will be run, and any implicitly
collected result will be returned as the value of the LOOP."
  '(go end-loop))



(defun subst-gensyms-for-nil (tree)
  (declare (special *ignores*))
  (cond
    ((null tree) (car (push (gensym) *ignores*)))
    ((atom tree) tree)
    (t (cons (subst-gensyms-for-nil (car tree))
	     (subst-gensyms-for-nil (cdr tree))))))
 
(defun loop-build-destructuring-bindings (crocks forms)
  (if crocks
      (let ((*ignores* ()))
	(declare (special *ignores*))
	`((destructuring-bind ,(subst-gensyms-for-nil (car crocks))
	      ,(cadr crocks)
	    (declare (ignore ,@*ignores*))
	    ,@(loop-build-destructuring-bindings (cddr crocks) forms))))
      forms))

(defun loop-translate (*loop-source-code* *loop-macro-environment* *loop-universe*)