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+;"mwexpand.scm" macro expander
+; Copyright 1992 William Clinger
+;
+; Permission to copy this software, in whole or in part, to use this
+; software for any lawful purpose, and to redistribute this software
+; is granted subject to the restriction that all copies made of this
+; software must include this copyright notice in full.
+;
+; I also request that you send me a copy of any improvements that you
+; make to this software so that they may be incorporated within it to
+; the benefit of the Scheme community.
+
+; The external entry points and kernel of the macro expander.
+;
+; Part of this code is snarfed from the Twobit macro expander.
+
+(define mw:define-syntax-scope
+  (let ((flag 'letrec))
+    (lambda args
+      (cond ((null? args) flag)
+	    ((not (null? (cdr args)))
+	     (apply mw:warn
+		    "Too many arguments passed to define-syntax-scope"
+		    args))
+	    ((memq (car args) '(letrec letrec* let*))
+	     (set! flag (car args)))
+	    (else (mw:warn "Unrecognized argument to define-syntax-scope"
+			  (car args)))))))
+
+(define mw:quit             ; assigned by macwork:expand
+  (lambda (v) v))
+
+(define (macwork:expand def-or-exp)
+  (call-with-current-continuation
+   (lambda (k)
+     (set! mw:quit k)
+     (set! mw:renaming-counter 0)
+     (mw:desugar-definitions def-or-exp mw:global-syntax-environment))))
+
+(define (mw:desugar-definitions exp env)
+  (letrec 
+    ((define-loop 
+       (lambda (exp rest first)
+	 (cond ((and (pair? exp)
+		     (eq? (mw:syntax-lookup env (car exp))
+			  mw:denote-of-begin)
+		     (pair? (cdr exp)))
+		(define-loop (cadr exp) (append (cddr exp) rest) first))
+	       ((and (pair? exp)
+		     (eq? (mw:syntax-lookup env (car exp))
+			  mw:denote-of-define))
+		(let ((exp (desugar-define exp env)))
+		  (cond ((and (null? first) (null? rest))
+			 exp)
+			((null? rest)
+			 (cons mw:begin1 (reverse (cons exp first))))
+			(else (define-loop (car rest)
+					   (cdr rest)
+					   (cons exp first))))))
+	       ((and (pair? exp)
+		     (eq? (mw:syntax-lookup env (car exp))
+			  mw:denote-of-define-syntax)
+		     (null? first))
+		(define-syntax-loop exp rest))
+	       ((and (null? first) (null? rest))
+		(mw:expand exp env))
+	       ((null? rest)
+		(cons mw:begin1 (reverse (cons (mw:expand exp env) first))))
+	       (else (cons mw:begin1
+			   (append (reverse first)
+				   (map (lambda (exp) (mw:expand exp env))
+					(cons exp rest))))))))
+     
+     (desugar-define
+      (lambda (exp env)
+	(cond 
+	 ((null? (cdr exp)) (mw:error "Malformed definition" exp))
+	 ; (define foo) syntax is transformed into (define foo (undefined)).
+	 ((null? (cddr exp))
+	  (let ((id (cadr exp)))
+	    (redefinition id)
+	    (mw:syntax-bind-globally! id (mw:make-identifier-denotation id))
+	    (list mw:define1 id mw:undefined)))
+	 ((pair? (cadr exp))
+	  ; mw:lambda0 is an unforgeable lambda, needed here because the
+	  ; lambda expression will undergo further expansion.
+	  (desugar-define `(,mw:define1 ,(car (cadr exp))
+				     (,mw:lambda0 ,(cdr (cadr exp))
+					       ,@(cddr exp)))
+			  env))
+	 ((> (length exp) 3) (mw:error "Malformed definition" exp))
+	 (else (let ((id (cadr exp)))
+		 (redefinition id)
+		 (mw:syntax-bind-globally! id (mw:make-identifier-denotation id))
+		 `(,mw:define1 ,id ,(mw:expand (caddr exp) env)))))))
+     
+     (define-syntax-loop 
+       (lambda (exp rest)
+	 (cond ((and (pair? exp)
+		     (eq? (mw:syntax-lookup env (car exp))
+			  mw:denote-of-begin)
+		     (pair? (cdr exp)))
+		(define-syntax-loop (cadr exp) (append (cddr exp) rest)))
+	       ((and (pair? exp)
+		     (eq? (mw:syntax-lookup env (car exp))
+			  mw:denote-of-define-syntax))
+		(if (pair? (cdr exp))
+		    (redefinition (cadr exp)))
+		(if (null? rest)
+		    (mw:define-syntax exp env)
+		    (begin (mw:define-syntax exp env)
+			   (define-syntax-loop (car rest) (cdr rest)))))
+	       ((null? rest)
+		(mw:expand exp env))
+	       (else (cons mw:begin1
+			   (map (lambda (exp) (mw:expand exp env))
+					(cons exp rest)))))))
+     
+     (redefinition
+      (lambda (id)
+	(if (symbol? id)
+	    (if (not (mw:identifier?
+		      (mw:syntax-lookup mw:global-syntax-environment id)))
+		(mw:warn "Redefining keyword" id))
+	    (mw:error "Malformed variable or keyword" id)))))
+    
+    ; body of letrec
+    
+    (define-loop exp '() '())))
+
+; Given an expression and a syntactic environment,
+; returns an expression in core Scheme.
+
+(define (mw:expand exp env)
+  (if (not (pair? exp))
+      (mw:atom exp env)
+      (let ((keyword (mw:syntax-lookup env (car exp))))
+	(case (mw:denote-class keyword)
+	  ((special)
+	   (cond
+	    ((eq? keyword mw:denote-of-quote)         (mw:quote exp))
+	    ((eq? keyword mw:denote-of-lambda)        (mw:lambda exp env))
+	    ((eq? keyword mw:denote-of-if)            (mw:if exp env))
+	    ((eq? keyword mw:denote-of-set!)          (mw:set exp env))
+	    ((eq? keyword mw:denote-of-begin)         (mw:begin exp env))
+	    ((eq? keyword mw:denote-of-let-syntax)    (mw:let-syntax exp env))
+	    ((eq? keyword mw:denote-of-letrec-syntax)
+	     (mw:letrec-syntax exp env))
+	    ; @@ let, let*, letrec, paint within quasiquotation -- kend
+	    ((eq? keyword mw:denote-of-let)           (mw:let    exp env))
+	    ((eq? keyword mw:denote-of-let*)          (mw:let*   exp env))
+	    ((eq? keyword mw:denote-of-letrec)        (mw:letrec exp env))
+	    ((eq? keyword mw:denote-of-quasiquote)    (mw:quasiquote exp env))
+	    ((eq? keyword mw:denote-of-do)            (mw:do     exp env))
+	    ((or (eq? keyword mw:denote-of-define)
+		 (eq? keyword mw:denote-of-define-syntax))
+	     ;; slight hack to allow expansion into defines -KenD
+	     (if mw:in-define? 
+	       (mw:error "Definition out of context" exp)
+	       (begin
+		 (set! mw:in-define? #t)
+		 (let ( (result (mw:desugar-definitions exp env)) )
+		   (set! mw:in-define? #f)
+		   result))
+	    ))
+	    (else (mw:bug "Bug detected in mw:expand" exp env))))
+	  ((macro) (mw:macro exp env))
+	  ((identifier) (mw:application exp env))
+	  (else (mw:bug "Bug detected in mw:expand" exp env))
+      ) )
+) )
+
+(define mw:in-define? #f)  ; should be fluid
+
+(define (mw:atom exp env)
+  (cond ((not (symbol? exp))
+	 ; Here exp ought to be a boolean, number, character, or string,
+	 ; but I'll allow for non-standard extensions by passing exp
+	 ; to the underlying Scheme system without further checking.
+	 exp)
+	(else (let ((denotation (mw:syntax-lookup env exp)))
+		(case (mw:denote-class denotation)
+		  ((special macro)
+		   (mw:error "Syntactic keyword used as a variable" exp env))
+		  ((identifier) (mw:identifier-name denotation))
+		  (else (mw:bug "Bug detected by mw:atom" exp env)))))))
+
+(define (mw:quote exp)
+  (if (= (mw:safe-length exp) 2)
+      (list mw:quote1 (mw:strip (cadr exp)))
+      (mw:error "Malformed quoted constant" exp)))
+
+(define (mw:lambda exp env)
+  (if (> (mw:safe-length exp) 2)
+      (let* ((formals (cadr exp))
+	     (alist (mw:rename-vars (mw:make-null-terminated formals)))
+	     (env (mw:syntax-rename env alist))
+	     (body (cddr exp)))
+	(list mw:lambda1
+	      (mw:rename-formals formals alist)
+	      (mw:body body env)))
+      (mw:error "Malformed lambda expression" exp)))
+
+(define (mw:body body env)
+  (define (loop body env defs)
+    (if (null? body)
+	(mw:error "Empty body"))
+    (let ((exp (car body)))
+      (if (and (pair? exp)
+	       (symbol? (car exp)))
+	  (let ((denotation (mw:syntax-lookup env (car exp))))
+	    (case (mw:denote-class denotation)
+	      ((special)
+	       (cond ((eq? denotation mw:denote-of-begin)
+		      (loop (append (cdr exp) (cdr body)) env defs))
+		     ((eq? denotation mw:denote-of-define)
+		      (loop (cdr body) env (cons exp defs)))
+		     (else (mw:finalize-body body env defs))))
+	      ((macro)
+	       (mw:transcribe exp
+			     env
+			     (lambda (exp env)
+			       (loop (cons exp (cdr body))
+				     env
+				     defs))))
+	      ((identifier)
+	       (mw:finalize-body body env defs))
+	      (else (mw:bug "Bug detected in mw:body" body env))))
+	  (mw:finalize-body body env defs))))
+  (loop body env '()))
+
+(define (mw:finalize-body body env defs)
+  (if (null? defs)
+      (let ((body (map (lambda (exp) (mw:expand exp env))
+		       body)))
+	(if (null? (cdr body))
+	    (car body)
+	    (cons mw:begin1 body)))
+      (let* ((alist (mw:rename-vars '(quote lambda set!)))
+	     (env (mw:syntax-alias env alist mw:standard-syntax-environment))
+	     (new-quote  (cdr (assq 'quote alist)))
+	     (new-lambda (cdr (assq 'lambda alist)))
+	     (new-set!   (cdr (assq 'set!   alist))))
+	(define (desugar-definition def)
+	  (if (> (mw:safe-length def) 2)
+	      (cond ((pair? (cadr def))
+		     (desugar-definition
+		      `(,(car def)
+			,(car (cadr def))
+			(,new-lambda
+			  ,(cdr (cadr def))
+			  ,@(cddr def)))))
+		    ((= (length def) 3)
+		     (cdr def))
+		    (else (mw:error "Malformed definition" def env)))
+	      (mw:error "Malformed definition" def env)))
+	(mw:letrec
+	 `(letrec ,(map desugar-definition (reverse defs)) ,@body)
+	  env)))
+  )
+
+(define (mw:if exp env)
+  (let ((n (mw:safe-length exp)))
+    (if (or (= n 3) (= n 4))
+	(cons mw:if1 (map (lambda (exp) (mw:expand exp env)) (cdr exp)))
+	(mw:error "Malformed if expression" exp env))))
+
+(define (mw:set exp env)
+  (if (= (mw:safe-length exp) 3)
+      `(,mw:set!1 ,(mw:expand (cadr exp) env) ,(mw:expand (caddr exp) env))
+      (mw:error "Malformed assignment" exp env)))
+
+(define (mw:begin exp env)
+  (if (positive? (mw:safe-length exp))
+      `(,mw:begin1 ,@(map (lambda (exp) (mw:expand exp env)) (cdr exp)))
+      (mw:error "Malformed begin expression" exp env)))
+
+(define (mw:application exp env)
+  (if (> (mw:safe-length exp) 0)
+      (map (lambda (exp) (mw:expand exp env))
+	   exp)
+      (mw:error "Malformed application")))
+
+; I think the environment argument should always be global here.
+
+(define (mw:define-syntax exp env)
+  (cond ((and (= (mw:safe-length exp) 3)
+	      (symbol? (cadr exp)))
+	 (mw:define-syntax1 (cadr exp)
+			   (caddr exp)
+			   env
+			   (mw:define-syntax-scope)))
+	((and (= (mw:safe-length exp) 4)
+	      (symbol? (cadr exp))
+	      (memq (caddr exp) '(letrec letrec* let*)))
+	 (mw:define-syntax1 (cadr exp)
+			   (cadddr exp)
+			   env
+			   (caddr exp)))
+	(else (mw:error "Malformed define-syntax" exp env))))
+
+(define (mw:define-syntax1 keyword spec env scope)
+  (case scope
+    ((letrec)  (mw:define-syntax-letrec keyword spec env))
+    ((letrec*) (mw:define-syntax-letrec* keyword spec env))
+    ((let*)    (mw:define-syntax-let* keyword spec env))
+    (else      (mw:bug "Weird scope" scope)))
+  (list mw:quote1 keyword))
+
+(define (mw:define-syntax-letrec keyword spec env)
+  (mw:syntax-bind-globally!
+   keyword
+   (mw:compile-transformer-spec spec env)))
+
+(define (mw:define-syntax-letrec* keyword spec env)
+  (let* ((env (mw:syntax-extend (mw:syntax-copy env)
+				(list keyword)
+				'((fake denotation))))
+	 (transformer (mw:compile-transformer-spec spec env)))
+    (mw:syntax-assign! env keyword transformer)
+    (mw:syntax-bind-globally! keyword transformer)))
+
+(define (mw:define-syntax-let* keyword spec env)
+  (mw:syntax-bind-globally!
+   keyword
+   (mw:compile-transformer-spec spec (mw:syntax-copy env))))
+
+(define (mw:let-syntax exp env)
+  (if (and (> (mw:safe-length exp) 2)
+	   (comlist:every (lambda (binding)
+		    (and (pair? binding)
+			 (symbol? (car binding))
+			 (pair? (cdr binding))
+			 (null? (cddr binding))))
+		    (cadr exp)))
+      (mw:body (cddr exp)
+	      (mw:syntax-extend env
+				(map car (cadr exp))
+				(map (lambda (spec)
+				       (mw:compile-transformer-spec
+					spec
+					env))
+				     (map cadr (cadr exp)))))
+      (mw:error "Malformed let-syntax" exp env)))
+
+(define (mw:letrec-syntax exp env)
+  (if (and (> (mw:safe-length exp) 2)
+	   (comlist:every (lambda (binding)
+		    (and (pair? binding)
+			 (symbol? (car binding))
+			 (pair? (cdr binding))
+			 (null? (cddr binding))))
+		    (cadr exp)))
+      (let ((env (mw:syntax-extend env
+				   (map car (cadr exp))
+				   (map (lambda (id)
+					  '(fake denotation))
+					(cadr exp)))))
+	(for-each (lambda (id spec)
+		    (mw:syntax-assign!
+		     env
+		     id
+		     (mw:compile-transformer-spec spec env)))
+		  (map car (cadr exp))
+		  (map cadr (cadr exp)))
+	(mw:body (cddr exp) env))
+      (mw:error "Malformed let-syntax" exp env)))
+
+(define (mw:macro exp env)
+  (mw:transcribe exp
+		env
+		(lambda (exp env)
+		  (mw:expand exp env))))
+
+; To do:
+; Clean up alist hacking et cetera.
+
+;;-----------------------------------------------------------------
+;; The following was added to allow expansion without flattening 
+;; LETs to LAMBDAs so that the origianl structure of the program 
+;; is preserved by macro expansion.  I.e. so that usual.scm is not 
+;; required. -- added KenD 
+
+(define (mw:process-let-bindings alist binding-list env)  ;; helper proc
+  (map (lambda (bind)
+	 (list (cdr (assq (car bind) alist)) ; renamed name
+	       (mw:body (cdr bind) env)))     ; alpha renamed value expression
+       binding-list)
+)
+
+(define (mw:strip-begin exp) ;; helper proc: mw:body sometimes puts one in
+  (if (and (pair? exp) (eq? (car exp) 'begin))
+    (cdr exp)
+    exp)
+)
+
+; LET
+(define (mw:let exp env)
+  (let* ( (name (if (or (pair? (cadr exp)) (null? (cadr exp)))
+		    #f 
+		    (cadr exp)))  ; named let?
+	  (binds (if name (caddr exp) (cadr exp)))
+	  (body  (if name (cdddr exp) (cddr exp)))
+	  (vars  (if (null? binds) #f (map car binds)))
+	  (alist (if vars (mw:rename-vars vars) #f))
+	  (newenv (if alist (mw:syntax-rename env alist) env))
+	)
+    (if name  ;; extend env with new name
+	(let ( (rename (mw:rename-vars (list name))) )
+	  (set! alist (append rename alist))
+	  (set! newenv (mw:syntax-rename newenv rename))
+    )   )
+    `(let
+	 ,@(if name (list (cdr (assq name alist))) '())
+	 ,(mw:process-let-bindings alist binds env)
+	 ,(mw:body body newenv))
+) )
+
+
+; LETREC differs from LET in that the binding values are processed in the
+; new rather than the original environment.
+
+(define (mw:letrec exp env)
+  (let* ( (binds (cadr exp))
+	  (body  (cddr exp))
+	  (vars  (if (null? binds) #f (map car binds)))
+	  (alist (if vars (mw:rename-vars vars) #f))
+	  (newenv (if alist (mw:syntax-rename env alist) env))
+	)
+    `(letrec
+	  ,(mw:process-let-bindings alist binds newenv)
+	  ,(mw:body body newenv))
+) )
+
+
+; LET* adds to ENV for each new binding.
+
+(define (mw:let* exp env)
+  (let ( (binds (cadr exp))
+	 (body  (cddr exp))
+       )
+    (let bind-loop ( (bindings binds) (newbinds '()) (newenv env) )
+       (if (null? bindings)
+	  `(let* ,(reverse newbinds) ,(mw:body body newenv))
+	   (let* ( (bind (car bindings))
+		   (var    (car bind)) 
+		   (valexp (cdr bind))
+		   (rename (mw:rename-vars (list var)))
+		   (next-newenv (mw:syntax-rename newenv rename))
+		 )
+	     (bind-loop (cdr bindings) 
+			(cons (list (cdr (assq var rename))
+				    (mw:body valexp newenv))
+			      newbinds)
+			next-newenv))
+) ) ) )
+
+
+; DO
+
+(define (mw:process-do-bindings var-init-steps alist oldenv newenv)  ;; helper proc
+  (map (lambda (vis)
+	 (let ( (v (car vis))
+		(i (cadr vis))
+		(s (if (null? (cddr vis)) (car vis) (caddr vis))))
+	   `( ,(cdr (assq v alist)) ; renamed name
+	      ,(mw:body (list i) oldenv)     ; init in outer/old env
+	      ,(mw:body (list s) newenv) ))) ; step in letrec/inner/new env
+       var-init-steps)
+)
+
+(define (mw:do exp env)
+  (let* ( (vis  (cadr exp))  ; (Var Init Step ...)
+	  (ts   (caddr exp)) ; (Test Sequence ...)
+	  (com  (cdddr exp)) ; (COMmand ...)
+	  (vars (if (null? vis) #f (map car vis)))
+	  (rename (if vars (mw:rename-vars vars) #f))
+	  (newenv (if vars (mw:syntax-rename env rename) env))
+	)
+    `(do ,(if vars (mw:process-do-bindings vis rename env newenv) '())
+	 ,(if  (null? ts)  '() (mw:strip-begin (mw:body (list ts) newenv)))
+	 ,@(if (null? com) '() (list (mw:body com newenv))))
+) )
+
+;
+; Quasiquotation (backquote)           
+;
+; At level 0, unquoted forms are left painted (not mw:strip'ed).
+; At higher levels, forms which are unquoted to level 0 are painted.
+; This includes forms within quotes.  E.g.:
+;   (lambda (a) 
+;     (quasiquote 
+;       (a (unquote a) b (quasiquote (a (unquote (unquote a)) b)))))
+;or equivalently:
+;  (lambda (a) `(a ,a b `(a ,,a b)))
+;=>
+;  (lambda (a|1) `(a ,a|1 b `(a ,,a|1 b)))
+
+(define (mw:quasiquote exp env)
+
+  (define (mw:atom exp env)
+    (if (not (symbol? exp))
+	exp
+	(let ((denotation (mw:syntax-lookup env exp)))
+	  (case (mw:denote-class denotation)
+	    ((special macro identifier) (mw:identifier-name denotation))
+	    (else (mw:bug "Bug detected by mw:atom" exp env))))
+  ) )
+
+  (define (quasi subexp level)
+     (cond
+	((null? subexp) subexp)
+	((not (or (pair? subexp) (vector? subexp)))
+	 (if (zero? level) (mw:atom subexp env) subexp) ; the work is here
+	)
+	((vector? subexp)
+	 (let* ((l (vector-length subexp))
+		(v (make-vector l)))
+	   (do ((i 0 (+ i 1)))
+	       ((= i l) v)
+	     (vector-set! v i (quasi (vector-ref subexp i) level))
+	     )
+	   )
+	 )
+	(else
+	  (let ( (keyword (mw:syntax-lookup env (car subexp))) )
+	    (cond
+	      ((eq? keyword mw:denote-of-unquote)
+	       (cons 'unquote (quasi (cdr subexp) (- level 1)))
+	      )
+	      ((eq? keyword mw:denote-of-unquote-splicing)
+	       (cons 'unquote-splicing (quasi (cdr subexp) (- level 1)))
+	      )
+	      ((eq? keyword mw:denote-of-quasiquote)
+	       (cons 'quasiquote (quasi (cdr subexp) (+ level 1)))
+	      )
+	      (else 
+	       (cons (quasi (car subexp) level) (quasi (cdr subexp) level)) 
+	      )
+	    )
+	) ) ; end else, let
+     ) ; end cond 
+  )
+
+  (quasi exp 0) ; need to unquote to level 0 to paint
+)
+
+;;                                      --- E O F ---