skint/src/k.sf

;---------------------------------------------------------------------------------------------
;
;  Stack-Based Model compiler/vm, derived from
;
;  Three Implementation Models for Scheme
;  TR87-0ll
;  1987
;  R. Kent Dybvig 
;
;  https://www.cs.unc.edu/techreports/87-011.pdf
;
;
;---------------------------------------------------------------------------------------------

(load "n.sf")


;---------------------------------------------------------------------------------------------
; 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-inline (string-cmp x y)
  (%prim? "fixnum(strcmp(stringchars(obj_from_$arg), stringchars(obj_from_$arg)))" x y))

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

(define (list1? x) (and (pair? x) (null? (cdr x))))
(define (list2? x) (and (pair? x) (list1? (cdr x))))
(define (list3? x) (and (pair? x) (list2? (cdr x))))
(define (list4? x) (and (pair? x) (list3? (cdr x))))


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

;  <core> -> (quote <object>)
;  <core> -> (ref <id>)
;  <core> -> (set! <id> <core>)
;  <core> -> (lambda <ids> <core>) where <ids> -> (<id> ...) | (<id> ... . <id>) | <id>
;  <core> -> (lambda* (<arity> <core>) ...) where <arity> -> (<cnt> <rest?>) 
;  <core> -> (begin <core> ...)
;  <core> -> (if <core> <core> <core>)
;  <core> -> (call <core> <core> ...)

;  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 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 unbound identifier is
; its name (as a symbol).  A bound identifier's denotation 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 den>
; <denotation>  ->  <symbol> | <binding>
; <binding>     ->  (<symbol> . <value>)
; <value>       ->  <special> | <core>
; <special>     ->  <builtin> | <transformer>
; <builtin>     ->  syntax | define | define-syntax |
;                   quote | set! | begin | if | lambda | body
; <transformer> ->  <procedure of exp and env returning exp>

(define-inline (val-core? val)            (pair? val))
(define-inline (val-special? val)         (not (pair? val)))

(define-inline (binding? x)               (pair? x))
(define-inline (make-binding s v)         (cons s v))
(define-inline (binding-val bnd)          (cdr bnd))
(define-inline (binding-special? bnd)     (val-special? (cdr bnd)))
(define-inline (binding-sym bnd)          (car bnd))
(define-inline (binding-set-val! bnd val) (set-cdr! bnd val))
(define-inline (find-top-binding s blist) (assq s blist))

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

(define (empty-xenv id)            (if (symbol? id) id (old-den 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))))

; 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)

(define (xform appos? sexp env)
  (cond [(id? sexp) 
         (let ([hval (xform-ref sexp env)])
           (if (and (procedure? hval) (not appos?))
               (xform appos? (hval sexp env) env) ; id-syntax
               hval))]
        [(not (pair? sexp)) (xform-quote sexp env)]
        [else (let* ([head (car sexp)] [tail (cdr sexp)] [hval (xform #t head env)])
                (case hval
                  [(syntax)        (car tail)]
                  [(quote)         (xform-quote (car tail) env)]
                  [(set!)          (xform-set! (car tail) (cadr tail) env)]
                  [(begin)         (xform-begin tail env)]
                  [(if)            (xform-if tail env)]
                  [(lambda)        (xform-lambda tail env)]
                  [(lambda*)       (xform-lambda* tail env)]
                  [(body)          (xform-body tail env)]
                  [(define)        (xform-define (car tail) (cadr tail) env)]
                  [(define-syntax) (xform-define-syntax (car tail) (cadr tail) env)]
                  [else            (if (procedure? hval)
                                       (xform appos? (hval sexp env) env)
                                       (xform-call hval tail env))]))]))

(define (xform-quote sexp env)
  (list 'quote 
    (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 (xform-ref id env)
  (let ([den (env id)])
    (cond [(symbol? den) (list 'ref den)]
          [else (binding-val den)])))

(define (xform-set! id exp env)
  (let ([den (env id)] [xexp (xform #f exp env)])
    (cond [(symbol? den) (list 'set! den xexp)]
          [(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)
                      (error 'transform "set! to non-identifier form")))])))

(define (xform-begin tail env)
  (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)))
      (error 'transform "improper begin form")))

(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 (error 'transform "malformed if form")]))
      (error 'transform "improper if form")))

(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)))
      (error 'transform "improper application")))

(define (xform-lambda tail env)
  (if (list? 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)))]))
      (error 'transform "improper lambda body")))

(define (xform-lambda* tail env)
  (if (list? tail)
      (cons 'lambda*
         (map (lambda (aexp)
                 (if (list2? aexp)
                     (list (normalize-arity (car aexp))
                           (xform #f (cadr aexp) env))
                     (error 'transform "improper lambda* clause")))
              tail))
      (error 'transform "improper lambda* form")))

(define (xform-body tail env)
  (if (null? tail)
      (list 'begin)
      (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)] [hval (xform #t head env)])
                (case hval
                  [(begin)
                   (loop env ids inits nids (append (cdr first) rest))]
                  [(define)
                   (let* ([id (cadr first)] [init (caddr first)]
                          [nid (gensym (id->sym id))] [env (add-var id nid env)])
                     (loop env (cons id ids) (cons init inits) (cons nid nids) rest))]
                  [(define-syntax)
                   (let* ([id (cadr first)] [init (caddr first)]
                          [env (add-binding id '(undefined) env)])
                     (loop env (cons id ids) (cons init inits) (cons #t nids) rest))]
                  [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 (sexp) (xform #f sexp env)) body))]
                  [xexp (if (and (pair? xexps) (null? (cdr xexps)))
                            (car xexps)
                            (cons 'begin xexps))])
             (if (null? lids)
                 xexp
                 (pair* 'call (list 'lambda (reverse lids) xexp)
                   (map (lambda (lid) '(begin)) lids))))]
          [(symbol? (car nids)) ; define
           (loop (cdr ids) (cdr inits) (cdr nids)
             (cons (xform-set! (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-define id exp env) ; top-level only
  (if (id? id)
      (list 'define (id->sym id) (xform #f exp env))
      (error 'transform "define of non-identifier form")))

(define (xform-define-syntax id exp env) ; top-level only
  (if (id? id)
      (list 'define-syntax (id->sym id) (xform #t exp env))
      (error 'transform "define-syntax of non-identifier form")))


; ellipsis denotation is used for comparisons only

(define denotation-of-default-ellipsis 
  (make-binding '... (lambda (sexp env) (error '... sexp))))

(define *transformers* 
  (list
    (make-binding 'syntax 'syntax) 
    (make-binding 'define 'define)
    (make-binding 'define-syntax 'define-syntax)
    (make-binding 'quote 'quote)
    (make-binding 'set! 'set!)
    (make-binding 'begin 'begin)
    (make-binding 'if 'if)
    (make-binding 'lambda 'lambda)
    (make-binding 'lambda* 'lambda*)
    (make-binding 'body 'body)
    denotation-of-default-ellipsis))

(define (top-transformer-env id)
  (let ([bnd (find-top-binding id *transformers*)])
    (cond [(binding? bnd)
           ; special case: syntax-rules in sexp form (left by init)
           (let ([val (binding-val bnd)])
             (if (and (pair? val) (eq? (car val) 'syntax-rules))  
                 (binding-set-val! bnd (transform #t val))))
           bnd]
          [(symbol? id)
           (let ([bnd (make-binding id (list 'ref id))])
             (set! *transformers* (cons bnd *transformers*))
             bnd)]
          [else (old-den id)])))

(define (install-transformer! s t)
  (binding-set-val! (top-transformer-env s) t))

(define (install-transformer-rules! s ell lits rules)
  (install-transformer! s
    (syntax-rules* top-transformer-env ell lits rules)))

(define (transform appos? sexp . optenv)
  (gensym #f) ; reset gs counter to make results reproducible
  (xform appos? sexp (if (null? optenv) top-transformer-env (car optenv))))


; 'syntax-rules' transformer produces another transformer 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? x)
    (if ellipsis
        (eq? x ellipsis)
        (and (id? x) (eq? (mac-env x) denotation-of-default-ellipsis))))

  ; 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 (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)))]
          [(pair? tmpl)
           (if (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)))
                 (let ([val-lists (map lookup vars-to-iterate)])
                   (append
                     (apply map (cons expand-using-vals val-lists))
                     (expand-part (cddr tmpl)))))
               (cons (expand-part (car tmpl)) (expand-part (cdr tmpl))))]
          [else tmpl]))))

  (lambda (use use-env)
    (let loop ([rules rules])
      (if (null? rules) (error 'transform "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))])))))

(install-transformer! 'syntax-rules
  (lambda (sexp env)
    (define syntax-id (new-id (make-binding 'syntax 'syntax)))
    ; sexp can be either
    (if (id? (cadr sexp))
        ; (_ ellipsis (litname ...) . rules)
        (list syntax-id (syntax-rules* env (cadr sexp) (caddr sexp) (cdddr sexp)))
        ; or (_ (litname ...) . rules)
        (list syntax-id (syntax-rules* env #f (cadr sexp) (cddr sexp))))))

; non-recursive transformer for define relies on old definition

(install-transformer! 'define
  (let ([env (add-binding 'define 'define top-transformer-env)])
    (syntax-rules* env #f '() '(
      [(_ (name . args) . forms)
       (define name (lambda args . forms))]
      [(_ name exp)
       (define name exp)]))))

; Remaining transformers are made with the help of syntax-rules*
; NB: order of installation is important -- each transformer can
; be self-recursive but can't use transformers defined later!

(define-syntax install-sr-transformer!
  (syntax-rules (quote syntax-rules)
    [(_ 'name (syntax-rules (lit ...) . rules))
     (install-transformer-rules! 'name #f '(lit ...) 'rules)]
    [(_ 'name (syntax-rules ellipsis (lit ...) . rules))
     (install-transformer-rules! 'name 'ellipsis '(lit ...) 'rules)]))    

(install-sr-transformer! 'letrec-syntax
  (syntax-rules ()
    [(_ ([key trans] ...) . forms) ; non-splicing!
     (body (define-syntax key trans) ... . forms)]))

(install-sr-transformer! 'let-syntax
  (syntax-rules ()
    [(_ () . forms) 
     (body . forms)]
    [(_ ([key trans] . bindings) . forms)
     (letrec-syntax ([temp trans])
       (let-syntax bindings 
         (letrec-syntax ([key temp]) . forms)))]))

(install-sr-transformer! 'letrec
  (syntax-rules ()
    [(_ ([var init] ...) . forms)
     (body (define var init) ... . forms)]))

(install-sr-transformer! 'let
  (syntax-rules ()
    [(_ ([var init] ...) . forms)
     ((lambda (var ...) . forms) init ...)]
    [(_ name ([var init] ...) . forms)
     ((letrec ((name (lambda (var ...) . forms))) name) init ...)]))

(install-sr-transformer! 'let*
  (syntax-rules ()
    [(_ () . forms) 
     (body . forms)]
    [(_ (first . more) . forms)
     (let (first) (let* more . forms))]))

(install-sr-transformer! 'and
  (syntax-rules ()
    [(_) #t]
    [(_ test) test]
    [(_ test . tests) (if test (and . tests) #f)]))

(install-sr-transformer! 'or
  (syntax-rules ()
    [(_) #f]
    [(_ test) test]
    [(_ test . tests) (let ([x test]) (if x x (or . tests)))]))

(install-sr-transformer! 'cond
  (syntax-rules (else =>)
    [(_) #f]
    [(_ (else . exps)) (begin . exps)]
    [(_ (x) . rest) (or x (cond . rest))]
    [(_ (x => proc) . rest) (let ([tmp x]) (cond [tmp (proc tmp)] . rest))]
    [(_ (x . exps) . rest) (if x (begin . exps) (cond . rest))]))

(install-sr-transformer! 'case-test
  (syntax-rules (else) 
    [(_ k else) #t]
    [(_ k atoms) (memv k 'atoms)]))

(install-sr-transformer! 'case
  (syntax-rules ()
    [(_ x (test . exprs) ...)
     (let ([key x]) (cond ((case-test key test) . exprs) ...))]))

(install-sr-transformer! 'do
  (syntax-rules ()
    [(_ ((var init . step) ...) ending expr ...)
     (let loop ([var init] ...)
       (cond ending [else expr ... (loop (begin var . step) ...)]))]))

(install-sr-transformer! 'quasiquote
  (syntax-rules (unquote unquote-splicing quasiquote)
    [(_ ,x) x]
    [(_ (,@x . y)) (append x `y)]
    [(_ `x . d) (cons 'quasiquote (quasiquote (x) d))]
    [(_ ,x   d) (cons 'unquote (quasiquote (x) . d))]
    [(_ ,@x  d) (cons 'unquote-splicing (quasiquote (x) . d))]
    [(_ (x . y) . d) (cons (quasiquote x . d) (quasiquote y . d))]
    [(_ #(x ...) . d) (list->vector (quasiquote (x ...) . d))]
    [(_ x . d) 'x]))

(install-sr-transformer! 'delay
  (syntax-rules ()
    [(_ exp)
     (make-delayed (lambda () exp))]))

(install-sr-transformer! 'when
  (syntax-rules ()
    [(_ test . rest) (if test (begin . rest))]))

(install-sr-transformer! 'unless
  (syntax-rules ()
    [(_ test . rest) (if (not test) (begin . rest))]))

(install-sr-transformer! 'case-lambda
  (syntax-rules ()
    [(_ [args . body] ...) (lambda* [args (lambda args . body)] ...)]))


;---------------------------------------------------------------------------------------------
; Runtime
;---------------------------------------------------------------------------------------------

(%localdef "#include \"i.h\"")

(define *globals* '())

(define global-location
  (lambda (sym)
    (let ([loc (assq sym *globals*)])
      (if (pair? loc)
          loc
          (let ([loc (cons sym 'undefined)])
            (set! *globals* (cons loc *globals*))
            loc)))))

(define-syntax index-global cdr)
(define-syntax index-set-global! set-cdr!)


;---------------------------------------------------------------------------------------------
; String representation of S-expressions and code arguments
;---------------------------------------------------------------------------------------------

(define (write-serialized-char x port)
  (cond [(or (char=? x #\%) (char=? x #\") (char=? x #\\) (char<? x #\space) (char>? x #\~))
         (write-char #\% port)
         (let ([s (fixnum->string (char->integer x) 16)])
           (if (fx=? (string-length s) 1) (write-char #\0 port))
           (write-string s port))]
        [else (write-char x port)]))

(define (write-serialized-size n port)         
  (write-string (fixnum->string n 10) port)
  (write-char #\: port))

(define (write-serialized-element x port)
  (write-serialized-sexp x port)
  (write-char #\; port))

(define (write-serialized-sexp x port)
  (cond [(eq? x #f) 
         (write-char #\f port)]
        [(eq? x #t) 
         (write-char #\t port)]
        [(eq? x '()) 
         (write-char #\n port)]
        [(char? x)
         (write-char #\c port)
         (write-serialized-char x port)]
        [(number? x)
         (write-char (if (exact? x) #\i #\j) port)
         (write-string (number->string x 10) port)]
        [(list? x)
         (write-char #\l port)
         (write-serialized-size (length x) port)
         (do ([x x (cdr x)]) [(null? x)]
           (write-serialized-element (car x) port))]
        [(pair? x)
         (write-char #\p port)
         (write-serialized-element (car x) port) 
         (write-serialized-element (cdr x) port)]
        [(vector? x)
         (write-char #\v port)
         (write-serialized-size (vector-length x) port)
         (do ([i 0 (fx+ i 1)]) [(fx=? i (vector-length x))]
           (write-serialized-element (vector-ref x i) port))]
        [(string? x)
         (write-char #\s port)
         (write-serialized-size (string-length x) port)
         (do ([i 0 (fx+ i 1)]) [(fx=? i (string-length x))]
           (write-serialized-char (string-ref x i) port))]
        [(symbol? x)
         (write-char #\y port)
         (let ([x (symbol->string x)])
           (write-serialized-size (string-length x) port)
           (do ([i 0 (fx+ i 1)]) [(fx=? i (string-length x))]
             (write-serialized-char (string-ref x i) port)))]
        [else (error 'encode-sexp "cannot encode literal: ~s" x)]))

(define (write-serialized-arg arg port)
  (if (and (number? arg) (exact? arg) (fx<=? 0 arg) (fx<=? arg 9))
      (write-char (string-ref "0123456789" arg) port)
      (begin (write-char #\( port)
            (write-serialized-sexp arg port)
            (write-char #\) port))))


;---------------------------------------------------------------------------------------------
; Compiler producing serialized code
;---------------------------------------------------------------------------------------------

(define find-free*
  (lambda (x* b)
    (if (null? x*)
        '()
        (set-union 
          (find-free (car x*) b) 
          (find-free* (cdr x*) b)))))

(define find-free
  (lambda (x b)
    (record-case x
      [quote (obj) 
       '()]
      [ref (id)
       (if (set-member? id b) '() (list id))]
      [set! (id exp)
       (set-union
         (if (set-member? id b) '() (list id))
         (find-free exp b))]
      [lambda (idsi exp)
       (find-free exp (set-union (flatten-idslist idsi) b))]
      [lambda* clauses
       (find-free* (map cadr clauses) b)]
      [if (test then else)
       (set-union
         (find-free test b)
         (set-union (find-free then b) (find-free else b)))]
      [begin exps
       (find-free* exps b)]
      [call (exp . args)
       (set-union (find-free exp b) (find-free* args b))])))

(define find-sets*
  (lambda (x* v)
    (if (null? x*)
        '()
        (set-union 
          (find-sets (car x*) v) 
          (find-sets* (cdr x*) v)))))

(define find-sets
  (lambda (x v)
    (record-case x
      [quote (obj) 
       '()]
      [ref (id)
       '()]
      [set! (id x)
       (set-union
         (if (set-member? id v) (list id) '())
         (find-sets x v))]
      [lambda (idsi exp)
       (find-sets exp (set-minus v (flatten-idslist idsi)))]
      [lambda* clauses
       (find-sets* (map cadr clauses) v)]
      [begin exps
       (find-sets* exps v)]
      [if (test then else)
       (set-union
         (find-sets test v)
         (set-union (find-sets then v) (find-sets else v)))]
      [call (exp . args)
       (set-union (find-sets exp v) (find-sets* args v))])))


(define find-integrable-encoding
  (%prim "{ /* define find-integrable-encoding */
    static obj c[] = { obj_from_objptr(vmcases+4) };
    $return objptr(c); }"))

(define encode-integrable
  (%prim "{ /* define encode-integrable */
    static obj c[] = { obj_from_objptr(vmcases+5) };
    $return objptr(c); }"))


(define codegen
  ; x: Scheme Core expression to compile
  ; l: local var list (with #f placeholders for nonvar slots)
  ; f: free var list
  ; s: set! var set
  ; g: global var set
  ; k: #f: x goes to ac, N: x is to be returned after (sdrop n)
  ; port: output code goes here
  (lambda (x l f s g k port)
    (record-case x
      [quote (obj)
       (case obj
          [(#t) (write-char #\t port)]
          [(#f) (write-char #\f port)]
          [(()) (write-char #\n port)]
          [else (write-char #\' port) (write-serialized-arg obj port)])
       (when k (write-char #\] port) (write-serialized-arg k port))]
      [ref (id)
       (cond [(posq id l) => ; local
              (lambda (n) 
                (write-char #\. port)
                (write-serialized-arg n port)
                (if (set-member? id s) (write-char #\^ port)))]
             [(posq id f) => ; free
              (lambda (n) 
                (write-char #\: port)
                (write-serialized-arg n port)
                (if (set-member? id s) (write-char #\^ port)))]
             [else ; global
              (write-char #\@ port)
              (write-serialized-arg id port)])
       (when k (write-char #\] port) (write-serialized-arg k port))]
      [set! (id x)
       (codegen x l f s g #f port)
       (cond [(posq id l) => ; local
              (lambda (n) 
                (write-char #\. port) (write-char #\! port)
                (write-serialized-arg n port))]
             [(posq id f) => ; free
              (lambda (n) 
                (write-char #\: port) (write-char #\! port)
                (write-serialized-arg n port))]
             [else ; global
              (write-char #\@ port) (write-char #\! port)
              (write-serialized-arg id port)])
       (when k (write-char #\] port) (write-serialized-arg k port))]
      [begin exps
       (let loop ([xl exps])
         (when (pair? xl)
           (let ([k (if (pair? (cdr xl)) #f k)])
             (codegen (car xl) l f s g k port)
             (loop (cdr xl)))))
       (when (and k (null? exps)) (write-char #\] port) (write-serialized-arg k port))]
      [if (test then else)
       (codegen test l f s g #f port)
       (write-char #\? port)
       (write-char #\{ port)
       (codegen then l f s g k port)
       (write-char #\} port)
       (cond [k ; tail call: 'then' arm exits, so br around is not needed
              (codegen else l f s g k port)]
             [(equal? else '(begin)) ; non-tail with void 'else' arm
              ] ; no code needed -- ac retains #f from failed test
             [else ; non-tail with 'else' expression; needs br 
              (write-char #\{ port)
              (codegen else l f s g k port)
              (write-char #\} port)])]              
      [lambda (idsi exp)
       (let* ([ids (flatten-idslist idsi)]
              [free (set-minus (find-free exp ids) g)]
              [sets (find-sets exp ids)])
         (do ([free (reverse free) (cdr free)] [l l (cons #f l)]) [(null? free)]
           ; note: called with empty set! var list
           ; to make sure no dereferences are generated
           (codegen (list 'ref (car free)) l f '() g #f port)
           (write-char #\, port))
         (write-char #\& port)
         (write-serialized-arg (length free) port)
         (write-char #\{ port)
         (cond [(list? idsi)
                (write-char #\% port)
                (write-serialized-arg (length idsi) port)]
               [else
                (write-char #\% port) (write-char #\! port)
                (write-serialized-arg (idslist-req-count idsi) port)])
         (do ([ids ids (cdr ids)] [n 0 (fx+ n 1)]) [(null? ids)]
           (when (set-member? (car ids) sets)
             (write-char #\# port)
             (write-serialized-arg n port)))
         (codegen exp ids free 
           (set-union sets (set-intersect s free))
           g (length ids) port)
         (write-char #\} port))
       (when k (write-char #\] port) (write-serialized-arg k port))]
      [lambda* clauses
       (do ([clauses (reverse clauses) (cdr clauses)] [l l (cons #f l)]) 
            [(null? clauses)]
         (codegen (cadr (car clauses)) l f s g #f port)
         (write-char #\, port))
       (write-char #\& port)
       (write-serialized-arg (length clauses) port)
       (write-char #\{ port)
       (do ([clauses clauses (cdr clauses)] [i 0 (fx+ i 1)]) 
            [(null? clauses)]
         (let* ([arity (caar clauses)] [cnt (car arity)] [rest? (cadr arity)])
           (write-char #\| port)
           (if rest? (write-char #\! port))
           (write-serialized-arg cnt port)
           (write-serialized-arg i port)))
       (write-char #\% port) (write-char #\% port)
       (write-char #\} port)
       (when k (write-char #\] port) (write-serialized-arg k port))]
      [call (exp . args)
       (cond [(and (eq? (car exp) 'lambda) (list? (cadr exp))
                   (fx=? (length args) (length (cadr exp))))
              ; let-like call; compile as special lambda + call combo
              (do ([args (reverse args) (cdr args)] [l l (cons #f l)]) 
                [(null? args)]
                (codegen (car args) l f s g #f port)
                (write-char #\, port))
              (let* ([ids (cadr exp)] [exp (caddr exp)]
                     [sets (find-sets exp ids)]
                     [news (set-union (set-minus s ids) sets)]
                     [newl (append ids l)]) ; with real names
                (do ([ids ids (cdr ids)] [n 0 (fx+ n 1)]) [(null? ids)]
                  (when (set-member? (car ids) sets)
                    (write-char #\# port)
                    (write-serialized-arg n port)))
                (if k 
                    (codegen exp newl f news g (fx+ k (length args)) port)
                    (begin 
                      (codegen exp newl f news g #f port)
                      (write-char #\_ port)
                      (write-serialized-arg (length args) port))))]
             [(and (eq? (car exp) 'ref) 
                   (not (posq (cadr exp) l)) (not (posq (cadr exp) f)) 
                   (find-integrable-encoding (cadr exp) (length args))) =>
              ; integrable function/procedure
              (lambda (ienc)
                ; regular convention is 1st arg in a, others on stack
                (do ([args (reverse args) (cdr args)] [l l (cons #f l)]) 
                  [(null? args)]
                  (codegen (car args) l f s g #f port)
                  (unless (null? (cdr args)) (write-char #\, port)))
                (encode-integrable (length args) ienc port)
                (when k (write-char #\] port) (write-serialized-arg k port)))]
             [k 
              ; tail call with k elements under arguments
              (do ([args (reverse args) (cdr args)] [l l (cons #f l)]) 
                [(null? args) (codegen exp l f s g #f port)]
                (codegen (car args) l f s g #f port)
                (write-char #\, port))
              (write-char #\[ port)
              (write-serialized-arg k port)
              (write-serialized-arg (length args) port)]
             [else
              ; non-tail call; 'save' puts 2 extra elements on the stack!
              (write-char #\$ port) (write-char #\{ port)
              (do ([args (reverse args) (cdr args)] [l (cons #f (cons #f l)) (cons #f l)]) 
                [(null? args) (codegen exp l f s g #f port)]
                (codegen (car args) l f s g #f port)
                (write-char #\, port))
              (write-char #\[ port)
              (write-serialized-arg 0 port)
              (write-serialized-arg (length args) port)
              (write-char #\} port)])])))

(define (compile-to-string x)
  (let ([p (open-output-string)])
    (codegen x '() '() '() (find-free x '()) #f p)                   
    (get-output-string p)))


;---------------------------------------------------------------------------------------------
; Code deserializer and Evaluator (use built-ins)
;---------------------------------------------------------------------------------------------

(define execute-thunk-closure
  (%prim "{ /* define execute-thunk-closure */
    static obj c[] = { obj_from_objptr(vmcases+0) }; 
    $return objptr(c); }"))

(define make-closure
  (%prim "{ /* define make-closure */
    static obj c[] = { obj_from_objptr(vmcases+1) };
    $return objptr(c); }"))

(define execute
  (lambda (code)
    (execute-thunk-closure (make-closure code))))

(define decode-sexp
  (%prim "{ /* define decode-sexp */
    static obj c[] = { obj_from_objptr(vmcases+2) };
    $return objptr(c); }"))

(define decode
  (%prim "{ /* define decode */
    static obj c[] = { obj_from_objptr(vmcases+3) };
    $return objptr(c); }"))

(define (evaluate x)
  (execute (decode (compile-to-string (transform #f x)))))


;---------------------------------------------------------------------------------------------
; File processor (Scheme => Serialized code)
;---------------------------------------------------------------------------------------------

(define *hide-refs* '(
  define-inline nullary-unary-adaptor nullary-unary-binary-adaptor
  unary-binary-adaptor unary-binary-ternary-adaptor 
  unary-binary-ternary-quaternary-adaptor binary-ternary-adaptor
  cmp-reducer addmul-reducer subdiv-reducer append-reducer
))

(define (display-code cstr oport)
  (let loop ([i 0] [l (string-length cstr)])
    (let ([r (fx- l i)])
      (cond [(<= r 70)
             (display "  \"" oport)
             (display (substring cstr i l))
             (display "\"," oport)]
            [else
             (display "  \"" oport)
             (display (substring cstr i (fx+ i 70)))
             (display "\"\n" oport)             
             (loop (fx+ i 70) l)]))))  


(define (process-define-syntax id xval oport)
  (newline oport)
  (display "  \"" oport) (display id oport) (display "\",\n" oport)
  ; hack xval's define-inline leftovers
  (set! xval 
    (let hack ([v xval])
      (cond [(procedure? v) 'syntax-rules]
            [(eq? v 'define-inline) '_]
            [(pair? v) (cons (hack (car v)) (hack (cdr v)))]
            [else v])))
  ; wrap symbolic definitions so init code can use them
  (when (symbol? xval)
    (set! xval (list 'syntax-rules '() (list '(_ . args) (cons xval 'args)) (list '_ xval))))
  (let ([p (open-output-string)]) (write-serialized-sexp xval p)
    (display-code (get-output-string p) oport) (newline oport)))

(define (process-statement xval oport)
  (define cstr (compile-to-string xval))
  (newline oport)
  (display "  0,\n" oport)
  (display-code cstr oport) (newline oport))

(define (process-define id xlam oport)
  (process-statement (list 'set! id xlam) oport))

(define (scan-top-form x)
  (cond 
    [(and (list2? x) (eq? (car x) 'load) (string? (cadr x)))
     (let ([iport (open-input-file (cadr x))])
       (let loop ([x (read iport)])
         (unless (eof-object? x)
           (scan-top-form x)
           (loop (read iport))))
       (close-input-port iport))]
    [(pair? x)
     (let ([hval (transform #t (car x))])
       (cond
         [(eq? hval 'begin)
          (for-each scan-top-form (cdr x))]
         [(eq? hval 'define-syntax)
          (let ([xval (transform #t (caddr x))])
            (install-transformer! (cadr x) xval))]
         [(procedure? hval)
          (scan-top-form (hval x top-transformer-env))]))]))

(define (process-top-form x oport)
  (cond 
    [(and (list2? x) (eq? (car x) 'load) (string? (cadr x)))
     (let ([iport (open-input-file (cadr x))])
       (let loop ([x (read iport)])
         (unless (eof-object? x)
           (scan-top-form x)
           (loop (read iport))))
       (close-input-port iport))]
    [(pair? x)
     (let ([hval (transform #t (car x))])
       (cond
         [(eq? hval 'begin)
          (let loop ([x* (cdr x)])
            (when (pair? x*) 
              (process-top-form (car x*) oport)
              (loop (cdr x*))))]
         [(eq? hval 'define-syntax)
          (let ([xval (transform #t (caddr x))])
            (install-transformer! (cadr x) xval)
            (unless (memq (cadr x) *hide-refs*)  
              (process-define-syntax (cadr x) (caddr x) oport)))]
         [(eq? hval 'define)
          (let ([xval (transform #f (caddr x))])
            (process-define (cadr x) xval oport))]
         [(procedure? hval)
          (process-top-form (hval x top-transformer-env) oport)]
         [else
          (process-statement (transform #f x) oport)]))]
    [else
     (process-statement (transform #f x) oport)]))

(define (path-strip-directory filename)
  (let loop ([l (reverse (string->list filename))] [r '()])
    (cond [(null? l) (list->string r)]
          [(memv (car l) '(#\\ #\/ #\:)) (list->string r)]
          [else (loop (cdr l) (cons (car l) r))])))

(define (path-strip-extension filename)
  (let ([l (reverse (string->list filename))])
    (let ([r (memv #\. l)])
      (if r (list->string (reverse (cdr r))) filename))))

(define (module-name filename)
  (path-strip-extension (path-strip-directory filename)))

(define (process-file fname)
  (define iport (open-input-file fname))
  (define oport (current-output-port))
  (define mname (module-name fname))
  (display "/* " oport) (display mname oport) 
  (display ".c -- generated via skint -c " oport) 
  (display (path-strip-directory fname) oport) 
  (display " */" oport) (newline oport) (newline oport)
  (display "char *" oport) (display mname oport) 
  (display "_code[] = {" oport) (newline oport)
  (let loop ([x (read iport)])
    (unless (eof-object? x)
      (process-top-form x oport)
      (loop (read iport))))
  (display "\n  0, 0\n};\n" oport)
  (close-input-port iport))


;---------------------------------------------------------------------------------------------
; Initial environment
;---------------------------------------------------------------------------------------------

; NB: 'nuate' restores stack with fn arg on top of return triple
(define continuation-closure-code (decode "%1.0K2]1"))

; adapter closure for values/call-with-values pair
(define callmv-adapter-closure (make-closure (decode "K5")))

(define install-global-lambdas
  (%prim "{ /* define install-global-lambdas */
    static obj c[] = { obj_from_objptr(vmcases+6) };
    $return objptr(c); }"))

(install-global-lambdas)

(define initialize-modules
  (%prim "{ /* define initialize-modules */
    static obj c[] = { obj_from_objptr(vmcases+7) };
    $return objptr(c); }"))

(initialize-modules)


;---------------------------------------------------------------------------------------------
; Tests 
;---------------------------------------------------------------------------------------------

(define test1
 '(let ()
    (define (sort-list obj pred)
      (define (loop l)
        (if (and (pair? l) (pair? (cdr l))) (split l '() '()) l))
      (define (split l one two)
        (if (pair? l)
            (split (cdr l) two (cons (car l) one))
            (merge (loop one) (loop two))))
      (define (merge one two)
        (cond
          [(null? one) two]
          [(pred (car two) (car one))
           (cons (car two) (merge (cdr two) one))]
          [else (cons (car one) (merge (cdr one) two))]))
      (loop obj))
    (sort-list
      '("one" "two" "three" "four" "five" "six"
        "seven" "eight" "nine" "ten" "eleven" "twelve")
      string<?)))

(define test2
 '(let ()
    (define tak
      (lambda (x y z)
        (if (< y x)
            (tak (tak (- x 1) y z)
                (tak (- y 1) z x)
                (tak (- z 1) x y))
            z)))
    (define runtak
      (lambda (n r)
        (let loop ([n n] [r r] [s 7])
          (if (= n 0) r
              (let ([v (tak 18 12 (- s 1))])
                (loop (- n 1) (+ r v) v))))))
    (runtak 10 0)))

(define test3
 '(let ()
    (define (nqueens n)
      (define (one-to n)
        (let loop ((i n) (l '()))
          (cond
            ((zero? i) l)
            (else (loop (- i 1) (cons i l))))))
      (define (try-it x y z)
        (if (null? x)
            (if (null? y) 1 0)
            (+ (if (ok? (car x) 1 z)
                   (try-it (append (cdr x) y) '() (cons (car x) z))
                   0)
              (try-it (cdr x) (cons (car x) y) z))))
      (define (ok? row dist placed)
        (if (null? placed) #t
            (and (not (= (car placed) (+ row dist)))
                 (not (= (car placed) (- row dist)))
                 (ok? row (+ dist 1) (cdr placed)))))
      (try-it (one-to n) '() '()))
    (define (run-test count)
      (let loop ((n count) (v 92))
        (cond
          ((zero? n) v)
          (else (loop (- n 1) (nqueens (- v 84)))))))
    (run-test 10)))

(define test4
 '(let ()
    (define y
      (lambda (e) 
        ((call/cc call/cc) 
        (lambda (f) 
          (e (lambda (x) (((call/cc (call/cc call/cc)) f) x)))))))
    (define fakt
      (y (lambda (self) (lambda (x) (if (= x 0) 1 (* x (self (- x 1))))))))
    (fakt 10)))

(define test5
 '(let ()
    (define y
      (lambda (e) 
        ((call/cc call/cc) 
        (lambda (f) 
          (e (lambda (x) (((call/cc (call/cc call/cc)) f) x)))))))
    (define fakty
      (y (lambda (self) 
            (lambda (x) (if (= x 0) 1 (* x (self (- x 1))))))))
    (define (fakti x)
      (let loop ((n 1) (x x))
          (if (= x 1)
            n
            (loop (* n x) (- x 1)))))
    (define (faktr x)
      (if (= x 1)
          1
          (* x (faktr (- x 1)))))
    (define faktl
      (lambda (x)
          ((lambda (self) (self self x))
          (lambda (self x)
            (if (= x 1)
                x
                (* (self self (- x 1)) x))))))
    (let ([y (fakty 10)] [i (fakti 10)] [r (faktr 10)] [l (faktl 10)])
      (cons y (cons i (cons r (cons l '())))))))

; (evaluate test1) =>
; ("eight" "eleven" "five" "four" "nine" "one" "seven" "six" "ten" "three" "twelve" "two")     
;
; (evaluate test2) =>
; 70
;
; (evaluate test3) =>
; 92
;
; (evaluate test4) =>
; 3628800
;
; (evaluate test5) =>
; (3628800 3628800 3628800 3628800)
;


;---------------------------------------------------------------------------------------------
; REPL
;---------------------------------------------------------------------------------------------

(define (run-tests)
  (define start (current-jiffy))
  (display "Running tests ...") (newline)
  (write (evaluate test1)) (newline)
  (write (evaluate test2)) (newline)
  (write (evaluate test3)) (newline)
  (write (evaluate test4)) (newline)
  (write (evaluate test5)) (newline)
  (display "Elapsed time: ") (write (* 1000 (/ (- (current-jiffy) start) (jiffies-per-second))))
  (display " ms.") (newline))

(define (repl-eval x)
  (let ([xexp (transform #f x)])
    (display "TRANSFORM =>") (newline)
    (write xexp) (newline)
    (if (eq? (car xexp) 'define) (set-car! xexp 'set!))
    (display "COMPILE-TO-STRING =>") (newline)
    (let ([cstr (compile-to-string xexp)] [start #f])
      (display cstr) (newline)
      (display "DECODE+EXECUTE =>") (newline) 
      (set! start (current-jiffy))
      (let* ([thunk (decode cstr)]
             ;[foo (begin (display "decoded: ") (write thunk) (newline))]
             [res (execute thunk)])
        (write res) (newline))
      (display "Elapsed time: ") (write (* 1000 (/ (- (current-jiffy) start) (jiffies-per-second))))
      (display " ms.") (newline))))

(define (repl-eval-top-form x)
  (cond 
    [(and (list2? x) (eq? (car x) 'load) (string? (cadr x)))
     (let ([iport (open-input-file (cadr x))])
       (repl-from-port iport)
       (close-input-port iport))]
    [(pair? x)
     (let ([hval (transform #t (car x))])
       (cond
         [(eq? hval 'begin)
          (let loop ([x* (cdr x)])
            (when (pair? x*) 
              (repl-eval-top-form (car x*))
              (loop (cdr x*))))]
         [(eq? hval 'define-syntax)
          (let ([xval (transform #t (caddr x))])
            (install-transformer! (cadr x) xval))]
         [(procedure? hval)
          (repl-eval-top-form (hval x top-transformer-env))]
         [else
          (repl-eval x)]))]
    [else
     (repl-eval x)]))

(define (repl-read iport)
  (when (eq? iport (current-input-port))
    (display "\n3imp> "))
  (read iport))

(define (repl-from-port iport)
  (let loop ([x (repl-read iport)])
    (unless (eof-object? x)
        (repl-eval-top-form x)
        (loop (repl-read iport)))))

(define (run-repl)
  (repl-from-port (current-input-port)))

(define (main argv)
  (let ([args (cdr (command-line))])
    (cond
      [(syntax-match? '("-c" *) args)
       (process-file (cadr args))]
      [else
       ;(run-tests)
       (run-repl)])))