;---------------------------------------------------------------------------------------------
; Transformer and Compiler
;---------------------------------------------------------------------------------------------

(load "s.scm")

;---------------------------------------------------------------------------------------------
; Utils
;---------------------------------------------------------------------------------------------

(define set-member?
  (lambda (x s)
    (cond
      [(null? s) #f]
      [(eq? x (car s)) #t]
      [else (set-member? x (cdr s))])))

(define set-cons
  (lambda (x s) 
    (if (set-member? x s) 
        s 
        (cons x s))))

(define set-union
  (lambda (s1 s2)
    (if (null? s1) 
        s2 
        (set-union (cdr s1) (set-cons (car s1) s2)))))

(define set-minus
  (lambda (s1 s2)
    (if (null? s1)
        '()
        (if (set-member? (car s1) s2)
            (set-minus (cdr s1) s2)
            (cons (car s1) (set-minus (cdr s1) s2))))))

(define set-intersect
  (lambda (s1 s2)
    (if (null? s1)
        '()
        (if (set-member? (car s1) s2)
            (cons (car s1) (set-intersect (cdr s1) s2))
            (set-intersect (cdr s1) s2)))))

(define-syntax record-case
  (syntax-rules (else)
    [(record-case (pa . ir) clause ...)
     (let ([id (pa . ir)]) 
       (record-case id clause ...))]
    [(record-case id)
     'record-case-miss]
    [(record-case id [else exp ...])
     (begin exp ...)]
    [(record-case id [key ids exp ...] clause ...)
     (if (eq? (car id) 'key)
         (apply (lambda ids exp ...) (cdr id))
         (record-case id clause ...))]))

(define syntax-match?
  (lambda (pat exp)
    (or (eq? pat '*)
        (equal? exp pat)
        (and (pair? pat)
             (cond
              [(and (eq? (car pat) '$)
                    (pair? (cdr pat))
                    (null? (cddr pat)))
               (eq? exp (cadr pat))]
              [(and (pair? (cdr pat))
                    (eq? (cadr pat) '...)
                    (null? (cddr pat)))
               (let ([pat (car pat)])
                 (define (f lst)
                   (or (null? lst)
                       (and (pair? lst)
                            (syntax-match? pat (car lst))
                            (f (cdr lst)))))  
                 (f exp))]
              [else
               (and (pair? exp)
                    (syntax-match? (car pat) (car exp))
                    (syntax-match? (cdr pat) (cdr exp)))])))))

; unique symbol generator (poor man's version)
(define gensym
  (let ([gsc 0])
    (lambda args ; (), (symbol), or (#f) for gsc reset
      (set! gsc (fx+ gsc 1))
      (if (null? args)
          (string->symbol 
            (string-append "#" (fixnum->string gsc 10)))
          (if (symbol? (car args))
              (string->symbol 
                (string-append (symbol->string (car args))
                  (string-append "#" (fixnum->string gsc 10))))
              (set! gsc 0))))))

(define posq
  (lambda (x l)
    (let loop ([l l] [n 0])
      (cond [(null? l) #f]
            [(eq? x (car l)) n]
            [else (loop (cdr l) (fx+ n 1))]))))

(define list-diff
  (lambda (l t)
    (if (or (null? l) (eq? l t))
        '()
        (cons (car l) (list-diff (cdr l) t)))))

(define (pair* x . more)
  (let loop ([x x] [rest more])
    (if (null? rest) x 
        (cons x (loop (car rest) (cdr rest))))))

(define (andmap p l)
  (if (pair? l) (and (p (car l)) (andmap p (cdr l))) #t))

(define (list1? x) (and (pair? x) (null? (cdr x))))
(define (list1+? x) (and (pair? x) (list? (cdr x))))
(define (list2? x) (and (pair? x) (list1? (cdr x))))
(define (list2+? x) (and (pair? x) (list1+? (cdr x))))


;---------------------------------------------------------------------------------------------
; Syntax of the Scheme Core language
;---------------------------------------------------------------------------------------------

;  <core> -> (quote <object>)
;  <core> -> (ref <id>)
;  <core> -> (set! <id> <core>)
;  <core> -> (set& <id>)
;  <core> -> (lambda <ids> <core>) where <ids> -> (<id> ...) | (<id> ... . <id>) | <id>
;  <core> -> (lambda* (<arity> <core>) ...) where <arity> -> (<cnt> <rest?>) 
;  <core> -> (syntax-lambda (<id> ...) <core>)
;  <core> -> (letcc <id> <core>) 
;  <core> -> (withcc <core> <core>) 
;  <core> -> (begin <core> ...)
;  <core> -> (if <core> <core> <core>)
;  <core> -> (call <core> <core> ...) 
;  <core> -> (integrable <ig> <core> ...) where <ig> is an index in the integrables table

;  NB: (begin) is legit, returns unspecified value
;  on top level, these two extra core forms are legal:

;  <core> -> (define <id> <core>)
;  <core> -> (define-syntax <id> <transformer>)

(define idslist?
  (lambda (x)
    (cond [(null? x) #t]
          [(pair? x) (and (id? (car x)) (idslist? (cdr x)))]
          [else (id? x)])))

(define normalize-arity
  (lambda (arity)
    (if (and (list2? arity) (fixnum? (car arity)) (boolean? (cadr arity)))
        arity
        (let loop ([cnt 0] [l arity])
          (cond [(pair? l) (loop (fx+ 1 cnt) (cdr l))]
                [(null? l) (list cnt #f)]
                [else (list cnt #t)])))))

; convention for 'flattened' <ids> is to put rest arg if any at the front
(define flatten-idslist
  (lambda (ilist)
    (if (list? ilist) ilist
        (let loop ([l ilist] [r '()])
          (cond [(pair? l) (loop (cdr l) (cons (car l) r))]
                [else (if (null? l) (reverse! r) (cons l (reverse! r)))])))))

(define idslist-req-count
  (lambda (ilist)
    (if (pair? ilist)
        (fx+ 1 (idslist-req-count (cdr ilist)))
        0)))

;---------------------------------------------------------------------------------------------
; Macro transformer (from Scheme to Scheme Core) derived from Al Petrofsky's EIOD 1.17
;---------------------------------------------------------------------------------------------

; An environment is a procedure that accepts any identifier and
; returns a denotation. The denotation of an identifier is its
; binding, which is a pair of the current value and the identifier's 
; name (needed by quote). Biding's value can be changed later.

; Special forms are either a symbol naming a builtin, or a transformer procedure 
; that takes two arguments: a macro use and the environment of the macro use.

; <identifier>  ->  <symbol> | <thunk returning (sym . den)>
; <denotation>  ->  <binding>
; <binding>     ->  (<symbol> . <value>)
; <value>       ->  <special> | <core>
; <special>     ->  <builtin> | <transformer>
; <builtin>     ->  syntax | quote | set! | set& | if | lambda | lambda* |
;                   letcc | withcc | body | begin | define | define-syntax |
;                   syntax-lambda | syntax-rules | syntax-length | syntax-error  
; <transformer> ->  <procedure of exp and env returning exp>

(define-syntax   val-core?               pair?)
(define-syntax   binding?                pair?)
(define-syntax   make-binding            cons)
(define-syntax   binding-val             cdr)
(define          (binding-special? bnd)  (not (pair? (cdr bnd))))
(define-syntax   binding-sym             car)
(define-syntax   binding-set-val!        set-cdr!)

(define (new-id sym den)           (define p (cons sym den)) (lambda () p))
(define (old-sym id)               (car (id)))
(define (old-den id)               (cdr (id)))
(define (id? x)                    (or (symbol? x) (procedure? x)))
(define (id->sym id)               (if (symbol? id) id (old-sym id)))

(define (extend-xenv env id bnd)   (lambda (i) (if (eq? id i) bnd (env i))))

(define (add-binding key val env) ; adds as-is     
  (extend-xenv env key (make-binding (id->sym key) val)))

(define (add-var var val env) ; adds renamed var as <core>
  (extend-xenv env var (make-binding (id->sym var) (list 'ref val))))

(define (xform-sexp->datum sexp)
  (let conv ([sexp sexp])
    (cond [(id? sexp) (id->sym sexp)]
          [(pair? sexp) (cons (conv (car sexp)) (conv (cdr sexp)))]
          [(vector? sexp) (list->vector (map conv (vector->list sexp)))]
          [else sexp])))

(define (x-error msg . args)
  (error* (string-append "transformer: " msg) args))

; xform receives Scheme s-expressions and returns either Core Scheme <core>
; (always a pair) or special-form, which is either a builtin (a symbol) or
; a transformer (a procedure). Appos? flag is true when the context can
; allow xform to return a transformer; otherwise, only <core> is accepted. 

(define (xform appos? sexp env)
  (cond [(id? sexp) 
         (let ([hval (xform-ref sexp env)])
           (cond [appos? ; app position: anything goes
                  hval]
                 [(integrable? hval) ; integrable id-syntax
                  (list 'ref (integrable-global hval))]
                 [(procedure? hval) ; id-syntax
                  (xform appos? (hval sexp env) env)]
                 [(not (pair? hval)) ; special used out of context 
                  (x-error "improper use of syntax form" hval)]
                 [else ; core 
                  hval]))]
        [(not (pair? sexp))
         (xform-quote (list sexp) env)]
        [else 
         (let* ([head (car sexp)] [tail (cdr sexp)] [hval (xform #t head env)])
           (case hval
             [(syntax)        (car tail)] ; internal use only
             [(quote)         (xform-quote         tail env)]
             [(set!)          (xform-set!          tail env)]
             [(set&)          (xform-set&          tail env)]
             [(if)            (xform-if            tail env)]
             [(lambda)        (xform-lambda        tail env)]
             [(lambda*)       (xform-lambda*       tail env)]
             [(letcc)         (xform-letcc         tail env)]
             [(withcc)        (xform-withcc        tail env)]
             [(body)          (xform-body          tail env)]
             [(begin)         (xform-begin         tail env)]
             [(define)        (xform-define        tail env)]
             [(define-syntax) (xform-define-syntax tail env)]
             [(syntax-lambda) (xform-syntax-lambda tail env)]
             [(syntax-rules)  (xform-syntax-rules  tail env)]
             [(syntax-length) (xform-syntax-length tail env)]
             [(syntax-error)  (xform-syntax-error  tail env)]
             [else            (if (integrable? hval)
                                  (xform-integrable hval tail env)
                                  (if (procedure? hval)
                                      (xform appos? (hval sexp env) env)
                                      (xform-call hval tail env)))]))]))

(define (xform-ref id env)
  (let ([den (env id)])
    (cond [(eq? (binding-val den) '...) (x-error "improper use of ...")]
          [else (binding-val den)])))

(define (xform-quote tail env)
  (if (list1? tail)
      (list 'quote (xform-sexp->datum (car tail)))
      (x-error "improper quote form" (cons 'quote tail))))

(define (xform-set! tail env)
  (if (and (list2? tail) (id? (car tail)))
      (let ([den (env (car tail))] [xexp (xform #f (cadr tail) env)])
        (cond [(binding-special? den) (binding-set-val! den xexp) '(begin)]
              [else (let ([val (binding-val den)])
                      (if (eq? (car val) 'ref)
                          (list 'set! (cadr val) xexp)
                          (x-error "set! to non-identifier form")))]))
      (x-error "improper set! form" (cons 'set! tail))))

(define (xform-set& tail env)
  (if (list1? tail)
      (let ([den (env (car tail))])      
        (cond [(binding-special? den) (x-error "set& of a non-variable")]
              [else (let ([val (binding-val den)])
                      (if (eq? (car val) 'ref)
                          (list 'set& (cadr val))
                          (x-error "set& of a non-variable")))]))
      (x-error "improper set& form" (cons 'set& tail))))

(define (xform-if tail env)
  (if (list? tail)
      (let ([xexps (map (lambda (sexp) (xform #f sexp env)) tail)])
        (case (length xexps)
          [(2) (cons 'if (append xexps '((begin))))]
          [(3) (cons 'if xexps)]
          [else (x-error "malformed if form" (cons 'if tail))]))
      (x-error "improper if form" (cons 'if tail))))

(define (xform-call xexp tail env)
  (if (list? tail)
      (let ([xexps (map (lambda (sexp) (xform #f sexp env)) tail)])
        (if (and (null? xexps) (eq? (car xexp) 'lambda) (null? (cadr xexp)))
            (caddr xexp) ; ((let () x)) => x
            (pair* 'call xexp xexps)))
      (x-error "improper application" (cons xexp tail))))

(define (integrable-argc-match? igt n)
  (case igt
    [(#\0) (=  n 0)]   [(#\1) (=  n 1)]   [(#\2) (=  n 2)]   [(#\3) (=  n 3)] 
    [(#\p) (>= n 0)]   [(#\m) (>= n 1)]   [(#\c) (>= n 2)]   [(#\x) (>= n 1)]
    [(#\u) (<= 0 n 1)] [(#\b) (<= 1 n 2)] [(#\t) (<= 2 n 3)]
    [(#\#) (>= n 0)]   [(#\@) #f]
    [else  #f])) 

(define (xform-integrable ig tail env)
  (if (integrable-argc-match? (integrable-type ig) (length tail))
      (cons 'integrable (cons ig (map (lambda (sexp) (xform #f sexp env)) tail)))
      (xform-call (list 'ref (integrable-global ig)) tail env)))

(define (xform-lambda tail env)
  (if (and (list1+? tail) (idslist? (car tail)))
      (let loop ([vars (car tail)] [ienv env] [ipars '()])
        (cond [(pair? vars)
               (let* ([var (car vars)] [nvar (gensym (id->sym var))])
                 (loop (cdr vars) (add-var var nvar ienv) (cons nvar ipars)))]
              [(null? vars)
               (list 'lambda (reverse ipars) (xform-body (cdr tail) ienv))]
              [else ; improper 
               (let* ([var vars] [nvar (gensym (id->sym var))] 
                      [ienv (add-var var nvar ienv)])
                 (list 'lambda (append (reverse ipars) nvar)
                   (xform-body (cdr tail) ienv)))]))
      (x-error "improper lambda body" (cons 'lambda tail))))

(define (xform-lambda* tail env)
  (if (list? tail)
      (cons 'lambda*
         (map (lambda (aexp)
                 (if (and (list2? aexp) 
                          (or (and (list2? (car aexp)) 
                                   (fixnum? (caar aexp)) 
                                   (boolean? (cadar aexp)))
                              (idslist? (car aexp))))
                     (list (normalize-arity (car aexp))
                           (xform #f (cadr aexp) env))
                     (x-error "improper lambda* clause" aexp)))
              tail))
      (x-error "improper lambda* form" (cons 'lambda* tail))))

(define (xform-letcc tail env)
  (if (and (list2+? tail) (id? (car tail)))
      (let* ([var (car tail)] [nvar (gensym (id->sym var))])
        (list 'letcc nvar 
          (xform-body (cdr tail) (add-var var nvar env))))
      (x-error "improper letcc form" (cons 'letcc tail))))

(define (xform-withcc tail env)
  (if (list2+? tail)
      (list 'withcc (xform #f (car tail) env)
        (xform-body (cdr tail) env))
      (x-error "improper withcc form" (cons 'withcc tail))))

(define (xform-body tail env)
  (cond
    [(null? tail) 
     (list 'begin)]
    [(list1? tail) ; can't have defines there
     (xform #f (car tail) env)]
    [(not (list? tail))
     (x-error "improper body form" (cons 'body tail))]
    [else
     (let loop ([env env] [ids '()] [inits '()] [nids '()] [body tail])
       (if (and (pair? body) (pair? (car body)))
           (let ([first (car body)] [rest (cdr body)])
             (let* ([head (car first)] [tail (cdr first)] [hval (xform #t head env)])
               (case hval
                 [(begin) ; internal
                  (if (list? tail) 
                      (loop env ids inits nids (append tail rest))
                      (x-error "improper begin form" first))]
                 [(define) ; internal
                  (cond [(and (list2? tail) (null? (car tail))) ; idless
                         (let ([init (cadr tail)])
                           (loop env (cons #f ids) (cons init inits) (cons #f nids) rest))]
                        [(and (list2? tail) (id? (car tail)))
                         (let* ([id (car tail)] [init (cadr tail)]
                                [nid (gensym (id->sym id))] [env (add-var id nid env)])
                           (loop env (cons id ids) (cons init inits) (cons nid nids) rest))]
                        [(and (list2+? tail) (pair? (car tail)) (id? (caar tail)) (idslist? (cdar tail)))
                         (let* ([id (caar tail)] [lambda-id (new-id 'lambda (make-binding 'lambda 'lambda))] 
                                [init (cons lambda-id (cons (cdar tail) (cdr tail)))]
                                [nid (gensym (id->sym id))] [env (add-var id nid env)])
                           (loop env (cons id ids) (cons init inits) (cons nid nids) rest))]
                        [else (x-error "improper define form" first)])]
                 [(define-syntax) ; internal
                  (if (and (list2? tail) (id? (car tail))) 
                      (let* ([id (car tail)] [init (cadr tail)]
                             [env (add-binding id '(undefined) env)])
                        (loop env (cons id ids) (cons init inits) (cons #t nids) rest))
                      (x-error "improper define-syntax form" first))]
                 [else
                  (if (procedure? hval)
                      (loop env ids inits nids (cons (hval first env) rest))
                      (xform-labels (reverse ids) (reverse inits) (reverse nids) body env))])))
           (xform-labels (reverse ids) (reverse inits) (reverse nids) body env)))]))

(define (xform-labels ids inits nids body env)
  (let loop ([ids ids] [inits inits] [nids nids] [sets '()] [lids '()])
    (cond [(null? ids) 
           (let* ([xexps (append (reverse sets) (map (lambda (x) (xform #f x env)) body))]
                  [xexp (if (list1? xexps) (car xexps) (cons 'begin xexps))])
             (if (null? lids) xexp
                 (pair* 'call (list 'lambda (reverse lids) xexp)
                   (map (lambda (lid) '(begin)) lids))))]
          [(not (car ids)) ; idless define
           (loop (cdr ids) (cdr inits) (cdr nids)
             (cons (xform #f (car inits) env) sets) lids)]
          [(symbol? (car nids)) ; define
           (loop (cdr ids) (cdr inits) (cdr nids)
             (cons (xform-set! (list (car ids) (car inits)) env) sets)
             (cons (car nids) lids))]
          [else ; define-syntax
           (binding-set-val! (env (car ids)) (xform #t (car inits) env))
           (loop (cdr ids) (cdr inits) (cdr nids) sets lids)])))

(define (xform-begin tail env) ; top-level
  (if (list? tail)
      (let ([xexps (map (lambda (sexp) (xform #f sexp env)) tail)])
        (if (and (pair? xexps) (null? (cdr xexps)))
            (car xexps) ; (begin x) => x
            (cons 'begin xexps)))
      (x-error "improper begin form" (cons 'begin! tail))))

(define (xform-define tail env) ; top-level
  (cond [(and (list2? tail) (null? (car tail))) ; idless
         (xform #f (cadr tail) env)]
        [(and (list2? tail) (id? (car tail)))
         (list 'define (id->sym (car tail)) 
           (xform #f (cadr tail) env))]
        [(and (list2+? tail) (pair? (car tail)) (id? (caar tail)) (idslist? (cdar tail)))
         (list 'define (id->sym (caar tail))
           (xform-lambda (cons (cdar tail) (cdr tail)) env))] 
        [else 
         (x-error "improper define form" (cons 'define tail))]))

(define (xform-define-syntax tail env) ; top-level
  (if (and (list2? tail) (id? (car tail)))
      (list 'define-syntax (id->sym (car tail)) (xform #t (cadr tail) env))
      (x-error "improper define-syntax form" (cons 'define-syntax tail))))

(define (xform-syntax-lambda tail env)
  (if (and (list2+? tail) (andmap id? (car tail)))
      (let ([vars (car tail)] [macenv env] [forms (cdr tail)])
        ; return a transformer that wraps xformed body in (syntax ...)
        (lambda (use useenv)
          (if (and (list1+? use) (fx=? (length vars) (length (cdr use))))
              (let loop ([vars vars] [exps (cdr use)] [env macenv])
                (if (null? vars)
                    (list 'syntax (xform-body forms env))
                    (loop (cdr vars) (cdr exps)
                      (add-binding (car vars) 
                        (xform #t (car exps) useenv) env))))  
              (x-error "invalif syntax-lambda application" use))))  
      (x-error "improper syntax-lambda body" (cons 'syntax-lambda tail))))

(define (xform-syntax-rules tail env)
  (cond [(and (list2+? tail) (id? (car tail)) (andmap id? (cadr tail)))
         (syntax-rules* env (car tail) (cadr tail) (cddr tail))]
        [(and (list1+? tail) (andmap id? (car tail)))
         (syntax-rules* env #f (car tail) (cdr tail))]
        [else
         (x-error "improper syntax-rules form" (cons 'syntax-rules tail))]))

(define (xform-syntax-length tail env)
  (if (and (list1? tail) (list? (car tail)))
      (list 'quote (length (car tail)))
      (x-error "improper syntax-length form" (cons 'syntax-length tail))))

(define (xform-syntax-error tail env)
  (let ([args (map xform-sexp->datum tail)])
    (if (and (list1+? args) (string? (car args)))
        (apply x-error args)
        (x-error "improper syntax-error form" (cons 'syntax-error tail)))))


; make transformer procedure from the rules

(define (syntax-rules* mac-env ellipsis pat-literals rules)

  (define (pat-literal? id) (memq id pat-literals))
  (define (not-pat-literal? id) (not (pat-literal? id)))
  (define (ellipsis-pair? x)
    (and (pair? x) (ellipsis? (car x))))
  (define (ellipsis-denotation? den)
    (and (binding? den) (eq? (binding-val den) '...)))
  (define (ellipsis? x)
    (if ellipsis
        (eq? x ellipsis)
        (and (id? x) (ellipsis-denotation? (mac-env x)))))

  ; List-ids returns a list of the non-ellipsis ids in a
  ; pattern or template for which (pred? id) is true.  If
  ; include-scalars is false, we only include ids that are
  ; within the scope of at least one ellipsis.
  (define (list-ids x include-scalars pred?)
    (let collect ([x x] [inc include-scalars] [l '()])
      (cond [(id? x) (if (and inc (pred? x)) (cons x l) l)]
            [(vector? x) (collect (vector->list x) inc l)]
            [(pair? x)
             (if (ellipsis-pair? (cdr x))
                 (collect (car x) #t (collect (cddr x) inc l))
                 (collect (car x) inc (collect (cdr x) inc l)))]
            [else l])))

  ; Returns #f or an alist mapping each pattern var to a part of
  ; the input.  Ellipsis vars are mapped to lists of parts (or
  ; lists of lists ...).
  (define (match-pattern pat use use-env)
    (call-with-current-continuation
      (lambda (return)
        (define (fail) (return #f))
        (let match ([pat pat] [sexp use] [bindings '()])
          (define (continue-if condition)
            (if condition bindings (fail)))
          (cond
            [(id? pat)
              (if (pat-literal? pat)
                  (continue-if (and (id? sexp) (eq? (use-env sexp) (mac-env pat))))
                  (cons (cons pat sexp) bindings))]
            [(vector? pat)
             (or (vector? sexp) (fail))
             (match (vector->list pat) (vector->list sexp) bindings)]
            [(not (pair? pat))
             (continue-if (equal? pat sexp))]
            [(ellipsis-pair? (cdr pat))
             (let* ([tail-len (length (cddr pat))]
                    [sexp-len (if (list? sexp) (length sexp) (fail))]
                    [seq-len (fx- sexp-len tail-len)]
                    [sexp-tail (begin (if (negative? seq-len) (fail)) (list-tail sexp seq-len))]
                    [seq (reverse (list-tail (reverse sexp) tail-len))]
                    [vars (list-ids (car pat) #t not-pat-literal?)])
                     (define (match1 sexp)
                       (map cdr (match (car pat) sexp '())))
                     (append
                       (apply map (cons list (cons vars (map match1 seq))))
                       (match (cddr pat) sexp-tail bindings)))]
            [(pair? sexp)
             (match (car pat) (car sexp)
               (match (cdr pat) (cdr sexp) bindings))]
            [else (fail)])))))

  (define (expand-template pat tmpl top-bindings)
    ; New-literals is an alist mapping each literal id in the
    ; template to a fresh id for inserting into the output.  It
    ; might have duplicate entries mapping an id to two different
    ; fresh ids, but that's okay because when we go to retrieve a
    ; fresh id, assq will always retrieve the first one.
    (define new-literals
      (map (lambda (id) (cons id (new-id (id->sym id) (mac-env id))))
           (list-ids tmpl #t
             (lambda (id) (not (assq id top-bindings))))))

    (define ellipsis-vars
      (list-ids pat #f not-pat-literal?))

    (define (list-ellipsis-vars subtmpl)
      (list-ids subtmpl #t 
        (lambda (id) (memq id ellipsis-vars))))

    (let expand ([tmpl tmpl] [bindings top-bindings])
      (let expand-part ([tmpl tmpl])
        (cond
          [(id? tmpl)
           (cdr (or (assq tmpl bindings)
                    (assq tmpl top-bindings)
                    (assq tmpl new-literals)))]
          [(vector? tmpl)
           (list->vector (expand-part (vector->list tmpl)))]
          [(and (pair? tmpl) (ellipsis-pair? (cdr tmpl)))
           (let ([vars-to-iterate (list-ellipsis-vars (car tmpl))])
             (define (lookup var)
               (cdr (assq var bindings)))
             (define (expand-using-vals . vals)
               (expand (car tmpl)
                 (map cons vars-to-iterate vals)))
             (if (null? vars-to-iterate)
                 ; ellipsis following non-repeatable part is an error, but we don't care
                 (cons (expand-part (car tmpl)) (expand-part (cddr tmpl))) ; repeat once
                 ; correct use of ellipsis
                 (let ([val-lists (map lookup vars-to-iterate)])
                   (append
                     (apply map (cons expand-using-vals val-lists))
                     (expand-part (cddr tmpl))))))]
          [(pair? tmpl)
           (cons (expand-part (car tmpl)) (expand-part (cdr tmpl)))]
          [else tmpl]))))

  (lambda (use use-env)
    (let loop ([rules rules])
      (if (null? rules) (x-error "invalid syntax" use))
      (let* ([rule (car rules)] [pat (car rule)] [tmpl (cadr rule)])
        (cond [(match-pattern pat use use-env) =>
               (lambda (bindings) (expand-template pat tmpl bindings))]
              [else (loop (cdr rules))])))))


; experimental lookup procedure for alist-like macro environments

(define (lookup-in-transformer-env id env) ;=> binding | #f
  (if (procedure? id)
      (old-den id) ; nonsymbolic ids can't be globally bound
      (let loop ([env env])
        (cond [(pair? env)
               (if (eq? (caar env) id)
                   (car env)
                   (loop (cdr env)))]
              [(eq? env #t) 
               ; implicitly append integrables and "naked" globals
               (let ([bnd (make-binding id (or (lookup-integrable id) (list 'ref id)))])
                 (set! *root-env* (cons bnd *root-env*))
                 bnd)]
              ;[(procedure? env)
              ; (env id)]
              [else ; finite env
               #f]))))

; make root env from a list of initial transformers

(define *root-env*
  (let loop ([l (initial-transformers)] [env #t])
    (if (null? l) env
        (let ([p (car l)] [l (cdr l)])
          (let ([k (car p)] [v (cdr p)])
            (cond
              [(or (symbol? v) (number? v)) 
               (loop l (cons (cons k v) env))]
              [(and (pair? v) (eq? (car v) 'syntax-rules))
               (body
                 (define (sr-env id) 
                   (lookup-in-transformer-env id *root-env*))
                 (define sr-v
                   (if (id? (cadr v))
                       (syntax-rules* sr-env (cadr v) (caddr v) (cdddr v))
                       (syntax-rules* sr-env #f (cadr v) (cddr v))))
                 (loop l (cons (cons k sr-v) env)))]
              [else 
               (loop l (cons (list k '? v) env))]))))))

(define (root-env id)
  (lookup-in-transformer-env id *root-env*))

(define (error* msg args)
  (apply error (cons msg args)))

(define (transform! x)
  (let ([t (xform #t x root-env)])
    (when (and (syntax-match? '(define-syntax * *) t) (id? (cadr t))) ; (procedure? (caddr t))
        (let ([b (lookup-in-transformer-env (cadr t) *root-env*)])
          (when b (binding-set-val! b (caddr t)))))
    t)) 
  
(define (visit f) 
  (define p (open-input-file f)) 
  (let loop ([x (read p)]) 
    (unless (eof-object? x)
      (let ([t (transform! x)])
        (write t) 
        (newline))
      (loop (read p)))) 
  (close-input-port p))