Added comments to continuation words.

[scheme.forth.jl.git] / src / scheme.4th

vocabulary scheme
scheme definitions

include term-colours.4th
include defer-is.4th
include goto.4th
include catch-throw.4th
include integer.4th
include float.4th

include debugging.4th

defer read
defer expand
defer analyze
defer eval
defer print

defer collect-garbage

\ ---- Types ---- {{{

variable nexttype
0 nexttype !
: make-type
    create nexttype @ ,
    1 nexttype +!
    does> @ ;

make-type fixnum-type
make-type flonum-type
make-type ratnum-type
make-type boolean-type
make-type character-type
make-type string-type
make-type nil-type
make-type none-type
make-type pair-type
make-type symbol-type
make-type primitive-proc-type
make-type compound-proc-type
make-type continuation-type
make-type port-type
: istype? ( obj type -- obj bool )
    over = ;

\ }}}

\ ---- Exceptions ---- {{{

variable nextexception
1 nextexception !
: make-exception 
    create nextexception @ ,
    1 nextexception +!
    does> @ ;

: except-message:
    bold fg red
    ." Exception: "
;

make-exception recoverable-exception
make-exception unrecoverable-exception

: throw reset-term cr throw ;

\ }}}

\ ---- List-structured memory ---- {{{

20000 constant scheme-memsize

create car-cells scheme-memsize allot
create car-type-cells scheme-memsize allot
create cdr-cells scheme-memsize allot
create cdr-type-cells scheme-memsize allot

create nextfrees scheme-memsize allot
:noname
    scheme-memsize 0 do
        i 1+ nextfrees i + !
    loop
; execute
        
variable nextfree
0 nextfree !

: inc-nextfree
    nextfrees nextfree @ + @
    nextfree !

    nextfree @ scheme-memsize >= if
      collect-garbage
    then

    nextfree @ scheme-memsize >= if
        except-message: ." Out of memory!" unrecoverable-exception throw
    then
;

: cons ( car-obj cdr-obj -- pair-obj )
    cdr-type-cells nextfree @ + !
    cdr-cells nextfree @ + !
    car-type-cells nextfree @ + !
    car-cells nextfree @ + !

    nextfree @ pair-type
    inc-nextfree
;

: car ( pair-obj -- car-obj )
    drop
    dup car-cells + @ swap
    car-type-cells + @
;

: cdr ( pair-obj -- car-obj )
    drop
    dup cdr-cells + @ swap
    cdr-type-cells + @
;

: set-car! ( obj pair-obj -- )
    drop dup
    rot swap  car-type-cells + !
    car-cells + !
;

: set-cdr! ( obj pair-obj -- )
    drop dup
    rot swap  cdr-type-cells + !
    cdr-cells + !
;

variable object-stack-base
: init-object-stack-base
  depth object-stack-base ! ;

: nil 0 nil-type ;
: nil? nil-type istype? ;

: none 0 none-type ;
: none? none-type istype? ;

: objvar create nil swap , , ;

: value@ ( objvar -- val ) @ ;
: type@ ( objvar -- type ) 1+ @ ;
: value! ( newval objvar -- ) ! ;
: type! ( newtype objvar -- ) 1+ ! ;
: obj! ( newobj objvar -- ) dup rot swap 1+ ! ! ; 
: obj@ ( objvar -- obj ) dup @ swap 1+ @ ; 

: objeq? ( obj obj -- bool )
    rot = -rot = and ;

: 2rot ( a1 a2 b1 b2 c1 c2 -- b1 b2 c1 c2 a1 a2 )
    >R >R ( a1 a2 b1 b2 )
    2swap ( b1 b2 a1 a2 )
    R> R> ( b1 b2 a1 a2 c1 c2 )
    2swap
;

: -2rot ( a1 a2 b1 b2 c1 c2 -- c1 c2 a1 a2 b1 b2 )
    2swap ( a1 a2 c1 c2 b1 b2 )
    >R >R ( a1 a2 c1 c2 )
    2swap ( c1 c2 a1 a2 )
    R> R>
;

: 2pick ( an bn an-1 bn-1 ... a0 b0 n -- an bn an-1 bn-1 ... a0 b0 an bn )
    2* 1+ dup
    >R pick R> pick ;

\ }}}

\ ---- Pre-defined symbols ---- {{{

objvar symbol-table

: duplicate-charlist ( charlist -- copy )
    nil? false = if
        2dup car 2swap cdr recurse cons
    then ;

: charlist-equiv ( charlist charlist -- bool )

    2over 2over

    \ One or both nil
    nil? -rot 2drop
    if
        nil? -rot 2drop
        if
            2drop 2drop true exit
        else
            2drop 2drop false exit
        then
    else
        nil? -rot 2drop
        if
            2drop 2drop false exit
        then
    then

    2over 2over

    \ Neither nil
    car drop -rot car drop = if
            cdr 2swap cdr recurse
        else
            2drop 2drop false
    then
;

: charlist>symbol ( charlist -- symbol-obj )

    symbol-table obj@

    begin
        nil? false =
    while
        2over 2over
        car drop pair-type
        charlist-equiv if
            2swap 2drop
            car
            exit
        else
            cdr
        then
    repeat

    2drop
    drop symbol-type 2dup
    symbol-table obj@ cons
    symbol-table obj!
;


: cstr>charlist ( addr n -- charlist )
    dup 0= if
        2drop nil
    else
        2dup drop @ character-type 2swap
        swap 1+ swap 1-
        recurse

        cons
    then
;

: create-symbol ( -- )
    bl word
    count

    cstr>charlist
    charlist>symbol

    create swap , ,
    does> dup @ swap 1+ @
;

create-symbol quote             quote-symbol
create-symbol quasiquote        quasiquote-symbol
create-symbol unquote           unquote-symbol
create-symbol unquote-splicing  unquote-splicing-symbol
create-symbol define            define-symbol
create-symbol define-macro      define-macro-symbol
create-symbol set!              set!-symbol
create-symbol ok                ok-symbol
create-symbol if                if-symbol
create-symbol lambda            lambda-symbol
create-symbol λ                 λ-symbol
create-symbol eof               eof-symbol
create-symbol no-match          no-match-symbol

\ Symbol to be bound to welcome message procedure by library
create-symbol welcome           welcome-symbol

\ }}}

\ ---- Port I/O ----  {{{

( Ports are pairs with the fid in the car and the peek buffer in the cdr. )

: fileport>fid ( fileport -- fid )
    drop pair-type car drop ;

: get-last-peek ( fileport -- char/nil )
    drop pair-type cdr ;

: set-last-peek ( char/nil fileport -- )
    drop pair-type set-cdr!
;

: fid>fileport ( fid -- fileport )
    fixnum-type nil cons drop port-type ;

: open-input-file ( addr n -- fileport )
    r/o open-file drop fid>fileport
;

: close-port ( fileport -- )
    fileport>fid close-file drop
;

objvar console-i/o-port
0 fixnum-type nil cons drop port-type console-i/o-port obj!

objvar current-input-port
console-i/o-port obj@ current-input-port obj!

: read-char ( port -- char ) 
    2dup get-last-peek nil? if
        2drop
        2dup console-i/o-port obj@ objeq? if
            2drop
            key character-type
        else
            fileport>fid pad 1 rot read-file 0= if
                eof-symbol
            else
                pad @ character-type
            then
        then
    else
        nil 2rot set-cdr!
    then
;

: peek-char ( port -- char )
    2dup get-last-peek nil? if
        2drop 2dup read-char
        2dup 2rot set-last-peek
    else
        2swap 2drop
    then
;

variable read-line-buffer-span
variable read-line-buffer-offset

( Hack to save original read-line while we transition to new one. )
: orig-read-line immediate
    ['] read-line , ;

: read-line ( port -- string )

    2dup get-last-peek
    nil? if
        2drop
        0 read-line-buffer-offset !
    else
        2over nil 2swap set-last-peek
        2dup drop '\n' = if
            2drop nil nil cons exit
        else
            drop pad !
            1 read-line-buffer-offset !
        then
    then

    2dup console-i/o-port obj@ objeq? if
        2drop
        pad read-line-buffer-offset @ + 200 expect cr
        span @ read-line-buffer-offset @ + read-line-buffer-span !
    else
        pad read-line-buffer-offset @ + 200 2over fileport>fid orig-read-line
        drop swap read-line-buffer-offset @ + read-line-buffer-span !
    then

    nil
    
    begin
        read-line-buffer-span @ 0>
    while
        pad read-line-buffer-span @ 1- + @ character-type 2swap cons
        -1 read-line-buffer-span +!
    repeat

    nil? if
        nil cons drop string-type
    else
        drop string-type
    then
;

: read-port ( fileport -- obj )
    current-input-port obj!
    read ;

: read-console ( -- obj )
    console-i/o-port obj@ read-port ;

\ }}}

\ ---- Environments ---- {{{

: enclosing-env ( env -- env )
    cdr ;

: first-frame ( env -- frame )
    car ;

: make-frame ( vars vals -- frame )
    cons ;

: add-frame-to-env ( frame env -- env )
    cons ;

: frame-vars ( frame -- vars )
    car ;

: frame-vals ( frame -- vals )
    cdr ;

: add-binding ( var val frame -- )
    2swap 2over frame-vals cons
    2over set-cdr!
    2swap 2over frame-vars cons
    2swap set-car!
;

: extend-env ( vars vals env -- env )
    -2rot make-frame
    2swap add-frame-to-env
;

: get-vals-frame ( var frame -- vals | nil )
    2dup frame-vars 
    2swap frame-vals ( var vars vals )

    begin
        nil? false =
    while

        -2rot ( vals var vars )
        2over 2over car objeq? if
            2drop 2drop
            exit
        then

        cdr 2rot cdr
    repeat

    2drop 2drop 2drop
    nil
;

: get-vals ( var env -- vals | nil )

    begin
        nil? false =
    while
        2over 2over first-frame
        get-vals-frame nil? false = if
            2swap 2drop 2swap 2drop
            exit
        then

        2drop

        enclosing-env
    repeat

    2swap 2drop
;

objvar var \ Used only for error messages
: lookup-var ( var env -- val )
    2over var obj!
    
    get-vals nil? if
        except-message: ." tried to read unbound variable '" var obj@ print ." '."
        recoverable-exception throw
    then

    car
;

: set-var ( var val env -- )
    2rot 2dup var obj! ( val env var )
    2swap ( val var env )
    get-vals nil? if
        except-message: ." tried to set unbound variable '" var obj@ print ." '."
        recoverable-exception throw
    else
        ( val vals )
        set-car!
    then
;
hide var

: define-var ( var val env -- )
    first-frame ( var val frame )
    2rot 2swap 2over 2over ( val var frame var frame )

    get-vals-frame nil? if
        2drop
        -2rot 2swap 2rot
        add-binding
    else
        ( val var frame vals )
        2swap 2drop 2swap 2drop
        set-car!
    then
;

: make-procedure ( params body env -- proc )
    nil
    cons cons cons
    drop compound-proc-type
;

objvar global-env
nil nil nil extend-env
global-env obj!

\ }}}

\ ---- Continuations ---- {{{

: cons-return-stack ( -- listobj )
  rsp@ 1- rsp0  = if
    nil exit
  then

  nil rsp@ 1- rsp0 do
    i 1+ @ fixnum-type 2swap cons
  loop

  rsp@ 1- rsp0 - fixnum-type 2swap cons
;

: cons-param-stack ( -- listobj )
  nil 

  depth 2- object-stack-base @ = if
    exit
  then

  depth 2- object-stack-base @ do
        PSP0 i + 1 + @
        PSP0 i + 2 + @

        2swap cons
    2 +loop

  depth 2- 2/ fixnum-type 2swap cons
;

: make-continuation ( -- continuation true-obj )
    \ true-obj allows calling code to detect whether
    \ it is being called immediately following make-continuation
    \ or by a restore-continuation.

  cons-param-stack
  cons-return-stack
  cons drop continuation-type

  true boolean-type
;

: continuation->pstack-list
  drop pair-type car ;

: continuation->rstack-list
  drop pair-type cdr ;

: stack-list-len ( stack-list -- n )
    car drop
;

: restore-param-stack ( continuation -- obj_stack )
  continuation->pstack-list
  2dup >R >R

  ( Allocate stack space first using psp!,
    then copy objects from list. )

  car drop 2*
  object-stack-base @ psp0 + + psp!

  R> R> 2dup cdr
  2swap
  stack-list-len 1- 0 swap do

      2dup car
      PSP0 object-stack-base @ + i 2* + 2 + !
      PSP0 object-stack-base @ + i 2* + 1 + !
      cdr

  -1 +loop

  2drop
;

( This word restores the return stack to that contained in the
continuation object, and thus NEVER RETURNS. )
: restore-return-stack ( continuation -- )

    continuation->rstack-list

    2dup cdr 2swap stack-list-len ( list n )

    dup RSP0 + RSP! \ expand return stack to accommodate entries

    ( list n )

    1-  \ initial offset n-1
    0   \ final offset 0
    swap
    do
        2dup cdr 2swap car drop
        RSP0 i 1+ + !
    -1 +loop

    2drop
;

( This word restores the parameter and return stacks
to those in the continuation object. The restoration of the 
return stack means that execution continues at the point
described in the continuation object, so this word NEVER RETURNS.

Note that both obj and a false-obj are added to the parameter
stack before the return stack is restored, so that make-continuation
knows that this execution path is the result of a continuation
restoration rather than the original call to make-continuation. )
: restore-continuation-with-arg ( continuation obj -- )

    >R >R \ Store obj on return stack

    2dup >R >R \ Store copy of continuation on return stack

    restore-param-stack

    R> R> \ Pop continuation from return stack

    R> R> \ Pop obj from return stack

    2swap

    false boolean-type \ Add flag signifying continuation restore

    2swap

    restore-return-stack
;

\ }}}

\ ---- Primitives ---- {{{

: make-primitive ( cfa -- )
    bl word
    count

    cstr>charlist
    charlist>symbol
  
    rot primitive-proc-type ( var prim )
    global-env obj@ define-var
;

: ensure-arg-count ( args n -- )
    dup 0= if
        drop nil objeq? false = if
            except-message: ." Too many arguments for primitive procedure." recoverable-exception throw
        then
    else
        -rot nil? if
            except-message: ." Too few arguments for primitive procedure." recoverable-exception  throw
        then
        
        cdr rot 1- recurse
    then
;

: ensure-arg-type-and-count ( tn tn-1 ... t2 t1 args n -- )
    dup 0= if
        drop nil objeq? false = if
            except-message: ." Too many arguments for primitive procedure." recoverable-exception throw
        then
    else
        -rot nil? if
            except-message: ." Too few arguments for primitive procedure." recoverable-exception throw
        then

        2dup cdr 2swap car ( ... t1 n args' arg1 )
        2rot 1- swap 2swap rot ( ... args' n-1 arg1 t1 )
        istype? false = if
            except-message: ." Incorrect type for primitive procedure." recoverable-exception throw
        then

        2drop recurse
    then

;

: push-args-to-stack ( args -- arg1 arg2 ... argn )
    begin
        nil? false =
    while
        2dup car 2swap cdr
    repeat

    2drop
;

: add-fa-checks ( cfa n -- cfa' )
    here current @ 1+ dup @ , !
    0 ,
    here -rot
    docol ,
    ['] 2dup , ['] lit , , ['] ensure-arg-count ,
    ['] push-args-to-stack ,
    ['] lit , , ['] execute ,
    ['] exit ,
;

: add-fa-type-checks ( cfa t1 t2 ... tn n -- cfa' )
    here current @ 1+ dup @ , !
    0 ,
    here >R
    docol ,
    ['] 2dup ,
    ['] >R , ['] >R ,

    dup ( cfa t1 t2 ... tn n m )
    
    begin
        ?dup 0>
    while
        rot ['] lit , , ( cfa t1 t2 ... tn-1 n m )
        1-
    repeat

    ['] R> , ['] R> ,

    ['] lit , , ['] ensure-arg-type-and-count ,

    ['] push-args-to-stack ,
    ['] lit , , ['] execute ,
    ['] exit ,

    R>
;

: make-fa-primitive ( cfa n -- )
    add-fa-checks make-primitive ;

: make-fa-type-primitive ( cfa t1 t2 ... tn n -- )
    add-fa-type-checks make-primitive ;

: arg-type-error
            bold fg red ." Incorrect argument type." reset-term cr
            abort
;

: ensure-arg-type ( arg type -- arg )
    istype? false = if
        except-message: ." Incorrect argument type for primitive procedure." recoverable-exception throw
    then
;


\ }}}

\ ---- Macros ---- {{{

objvar macro-table

( Look up macro in macro table. Returns nil if
  no macro is found. )
: lookup-macro ( name_symbol -- proc )

    symbol-type istype? invert if
        \ Early exit if argument is not a symbol
        2drop nil exit
    then
    
    macro-table obj@

    begin
        nil? false =
    while
        2over 2over
        car car objeq? if
            2swap 2drop
            car cdr
            exit
        then

        cdr
    repeat

    2swap 2drop
;

: make-macro ( name_symbol params body env -- )
    make-procedure

    2swap ( proc name_symbol )

    macro-table obj@

    begin
        nil? false =
    while
        2over 2over ( proc name table name table )
        car car objeq? if
            2swap 2drop ( proc table )
            car ( proc entry )
            set-cdr!
            exit
        then

        cdr
    repeat

    2drop

    2swap cons
    macro-table obj@ cons
    macro-table obj!
;

\ }}}

\ ---- Read ---- {{{

variable parse-idx
variable stored-parse-idx
create parse-str 161 allot
variable parse-str-span

create parse-idx-stack 10 allot 
variable parse-idx-sp
parse-idx-stack parse-idx-sp !

: push-parse-idx
    parse-idx @ parse-idx-sp @ !
    1 parse-idx-sp +!
;

: pop-parse-idx
    parse-idx-sp @ parse-idx-stack <= abort" Parse index stack underflow."

    1 parse-idx-sp -!

    parse-idx-sp @ @ parse-idx ! ;


: append-newline
    '\n' parse-str parse-str-span @ + !
    1 parse-str-span +! ;

: append-eof
    4 parse-str parse-str-span @ + !
    1 parse-str-span +!  ;

: empty-parse-str
    0 parse-str-span !
    0 parse-idx ! ;

: getline
    current-input-port obj@ console-i/o-port obj@ objeq? if
        parse-str 160 expect cr
        span @ parse-str-span !
    else
        parse-str 160 current-input-port obj@ fileport>fid orig-read-line
        drop swap parse-str-span !

        parse-str-span @ 0= and if append-eof then
    then
    append-newline
    0 parse-idx ! ;

: inc-parse-idx
    1 parse-idx +! ;

: dec-parse-idx
    1 parse-idx -! ;

: charavailable? ( -- bool )
    parse-str-span @ parse-idx @ > ;

: nextchar ( -- char )
    charavailable? false = if getline then
    parse-str parse-idx @ + @ ;

: '\t' 9 ;
: whitespace? ( -- bool )
    nextchar BL = 
    nextchar '\n' =
    nextchar '\t' =
    or or ;

: EOF 4 ; 
: eof? ( -- bool )
    nextchar EOF = ;

: delim? ( -- bool )
    whitespace?
    nextchar [char] ( = or
    nextchar [char] ) = or
;

: commentstart? ( -- bool )
    nextchar [char] ; = ;

: eatspaces

    false \ Indicates whether or not we're eating a comment

    begin
        dup whitespace? or commentstart? or
    while
        dup nextchar '\n' = and if
            invert \ Stop eating comment
        else
            dup false = commentstart? and if   
                invert \ Begin eating comment
            then
        then

        inc-parse-idx
    repeat
    drop
;

: digit? ( -- bool )
    nextchar [char] 0 >=
    nextchar [char] 9 <=
    and ;

: minus? ( -- bool )
    nextchar [char] - = ;

: plus? ( -- bool )
    nextchar [char] + = ;

: fixnum? ( -- bool )
    minus? plus? or if
        inc-parse-idx

        delim? if
            dec-parse-idx
            false exit
        else
            dec-parse-idx
        then
    else
        digit? false = if
            false exit
        then
    then

    push-parse-idx
    inc-parse-idx

    begin digit? while
        inc-parse-idx
    repeat

    delim? pop-parse-idx
;

: flonum? ( -- bool )
    push-parse-idx

    minus? plus? or if
        inc-parse-idx
    then

    \ Record starting parse idx:
    \ Want to detect whether any characters (following +/-) were eaten.
    parse-idx @

    begin digit? while
            inc-parse-idx
    repeat

    [char] . nextchar = if
        inc-parse-idx
        begin digit? while
                inc-parse-idx
        repeat
    then

    [char] e nextchar = [char] E nextchar = or if
        inc-parse-idx

        minus? plus? or if
            inc-parse-idx
        then

        digit? invert if
            drop pop-parse-idx false exit
        then

        begin digit? while
                inc-parse-idx
        repeat
    then

    \ This is a real number if characters were
    \ eaten and the next characer is a delimiter.
    parse-idx @ < delim? and

    pop-parse-idx
;

: ratnum? ( -- bool )
    push-parse-idx

    minus? plus? or if
        inc-parse-idx
    then

    digit? invert if
        pop-parse-idx false exit
    else
        inc-parse-idx
    then

    begin digit? while
        inc-parse-idx
    repeat

    [char] / nextchar <> if
        pop-parse-idx false exit
    else
        inc-parse-idx
    then

    digit? invert if
        pop-parse-idx false exit
    else
        inc-parse-idx
    then

    begin digit? while
        inc-parse-idx
    repeat

    delim? pop-parse-idx
;

: boolean? ( -- bool )
    nextchar [char] # <> if false exit then

    push-parse-idx
    inc-parse-idx

    nextchar [char] t <>
    nextchar [char] f <>
    and if pop-parse-idx false exit then

    inc-parse-idx
    delim? if
        pop-parse-idx
        true
    else
        pop-parse-idx
        false
    then
;

: str-equiv? ( str -- bool )

    push-parse-idx

    true -rot

    swap dup rot + swap

    do
        i @ nextchar <> if
            drop false
            leave
        then

        inc-parse-idx
    loop

    delim? false = if drop false then

    pop-parse-idx
;

: character? ( -- bool )
    nextchar [char] # <> if false exit then

    push-parse-idx
    inc-parse-idx

    nextchar [char] \ <> if pop-parse-idx false exit then

    inc-parse-idx

    S" newline" str-equiv? if pop-parse-idx true exit then
    S" space" str-equiv? if pop-parse-idx true exit then
    S" tab" str-equiv? if pop-parse-idx true exit then

    charavailable? false = if pop-parse-idx false exit then

    pop-parse-idx true
;

: pair? ( -- bool )
    nextchar [char] ( = ;

: string? ( -- bool )
    nextchar [char] " = ;

: readfixnum ( -- fixnum )
    plus? minus? or if
        minus?
        inc-parse-idx
    else
        false
    then

    0

    begin digit? while
        10 * nextchar [char] 0 - +
        inc-parse-idx
    repeat

    swap if negate then

    fixnum-type
;

: readflonum ( -- flonum )
    readfixnum drop
    dup 0< swap abs i->f

    [char] . nextchar = if
        inc-parse-idx

        10.0 ( f exp )

        begin digit? while
            nextchar [char] 0 - i->f ( f exp d )
            over f/ rot f+ ( exp f' )
            swap 10.0 f* ( f' exp' )
            inc-parse-idx
        repeat

        drop
    then

    [char] e nextchar = [char] E nextchar = or if
        inc-parse-idx
        10.0
        readfixnum drop i->f
        f^ f*
    then

    swap if
        -1.0 f*
    then

    flonum-type
;

: make-rational ( fixnum fixnum -- ratnum|fixnum )
    drop swap drop
    simplify

    dup 1 = if
        drop fixnum-type
    else
        fixnum-type swap fixnum-type
        cons drop ratnum-type
    then
;

: readratnum ( -- ratnum )
    readfixnum inc-parse-idx readfixnum
    make-rational
;

: readbool ( -- bool-obj )
    inc-parse-idx
    
    nextchar [char] f = if
        false
    else
        true
    then

    inc-parse-idx

    boolean-type
;

: readchar ( -- char-obj )
    inc-parse-idx
    inc-parse-idx

    S" newline" str-equiv? if 7 parse-idx +! '\n' character-type exit then
    S" space" str-equiv? if 5 parse-idx +! bl character-type exit then
    S" tab" str-equiv? if 3 parse-idx +! 9 character-type exit then

    nextchar character-type

    inc-parse-idx
;

: readstring ( -- charlist )

    nil nil

    begin
        nextchar [char] " <>
    while
        nextchar [char] \ = if
            inc-parse-idx
            nextchar case
                [char] n of '\n' endof
                [char] " of [char] " endof
                [char] \
            endcase
        else
            nextchar
        then
        inc-parse-idx character-type
        nil cons

        ( firstchar prevchar thischar )

        2swap nil? if
            2drop 2swap 2drop 2dup  ( thischar thischar )
        else
            ( firstchar thischar prevchar )
            2over 2swap  set-cdr! ( firstchar thischar )
        then
    repeat

    \ Discard previous character
    2drop

    inc-parse-idx
    delim? false = if
        bold fg red
        ." No delimiter following right double quote. Aborting." cr
        reset-term abort
    then

    dec-parse-idx

    nil? if
        nil cons
    then
    drop string-type
;

: readsymbol ( -- charlist )
    delim? if nil exit then

    nextchar inc-parse-idx character-type

    recurse

    cons
;

: readpair ( -- pairobj )
    eatspaces

    \ Empty lists
    nextchar [char] ) = if
        inc-parse-idx

        delim? false = if
            bold fg red
            ." No delimiter following right paren. Aborting." cr
            reset-term abort
        then

        dec-parse-idx

        0 nil-type exit
    then

    \ Read first pair element
    read

    \ Pairs
    eatspaces
    nextchar [char] . = if
        inc-parse-idx

        delim? false = if
            bold fg red
            ." No delimiter following '.'. Aborting." cr
            reset-term abort
        then

        eatspaces read
    else
        recurse
    then

    eatspaces

    cons
;

\ Parse a scheme expression
:noname ( -- obj )

    eatspaces

    fixnum? if
        readfixnum
        exit
    then

    flonum? if
        readflonum
        exit
    then

    ratnum? if
        readratnum
        exit
    then

    boolean? if
        readbool
        exit
    then

    character? if
        readchar
        exit
    then

    string? if
        inc-parse-idx

        readstring

        nextchar [char] " <> if
            bold red ." Missing closing double-quote." reset-term cr
            abort
        then

        inc-parse-idx

        exit
    then

    pair? if
        inc-parse-idx

        eatspaces

        readpair

        eatspaces

        nextchar [char] ) <> if
            bold red ." Missing closing paren." reset-term cr
            abort
        then

        inc-parse-idx

        exit
    then

    nextchar [char] ' = if
        inc-parse-idx
        quote-symbol recurse nil cons cons exit
    then

    nextchar [char] ` = if
        inc-parse-idx
        quasiquote-symbol recurse nil cons cons exit
    then

    nextchar [char] , = if
        inc-parse-idx
        nextchar [char] @ = if
            inc-parse-idx
            unquote-splicing-symbol recurse nil cons cons exit
        else
            unquote-symbol recurse nil cons cons exit
        then
    then

    eof? if
        EOF character-type
        inc-parse-idx
        exit
    then

    nextchar [char] ) = if
        inc-parse-idx
        except-message: ." unmatched closing parenthesis." recoverable-exception throw
    then

    \ Anything else is parsed as a symbol
    readsymbol charlist>symbol

    \ Replace λ with lambda
    2dup λ-symbol objeq? if
        2drop lambda-symbol
    then
    

; is read

\ }}}

\ ---- Syntax ---- {{{

: self-evaluating? ( obj -- obj bool )
    boolean-type istype? if true exit then
    fixnum-type istype? if true exit then
    flonum-type istype? if true exit then
    ratnum-type istype? if true exit then
    character-type istype? if true exit then
    string-type istype? if true exit then
    nil-type istype? if true exit then
    none-type istype? if true exit then

    false
;

: tagged-list? ( obj tag-obj -- obj bool )
    2over 
    pair-type istype? false = if
        2drop 2drop false
    else
        car objeq?
    then ;

: quote? ( obj -- obj bool )
    quote-symbol tagged-list?  ;

: quote-body ( quote-obj -- quote-body-obj )
    cdr car ;

: variable? ( obj -- obj bool )
    symbol-type istype? ;

: definition? ( obj -- obj bool )
    define-symbol tagged-list? ;

: definition-var ( obj -- var )
    cdr car ;

: definition-val ( obj -- val )
    cdr cdr car ;

: assignment? ( obj -- obj bool )
    set!-symbol tagged-list? ;

: assignment-var ( obj -- var )
    cdr car ;
    
: assignment-val ( obj -- val )
    cdr cdr car ;

: macro-definition? ( obj -- obj bool )
    define-macro-symbol tagged-list? ;

: macro-definition-name ( exp -- mname )
    cdr car car ;

: macro-definition-params ( exp -- params )
    cdr car cdr ;

: macro-definition-body ( exp -- body )
    cdr cdr ;

: if? ( obj -- obj bool )
    if-symbol tagged-list? ;

: if-predicate ( ifobj -- pred )
    cdr car ;

: if-consequent ( ifobj -- conseq )
    cdr cdr car ;

: if-alternative ( ifobj -- alt|none )
    cdr cdr cdr
    nil? if
        2drop none
    else
        car
    then ;

: false? ( boolobj -- boolean )
    boolean-type istype? if
        false boolean-type objeq?
    else
        2drop false
    then
;

: true? ( boolobj -- bool )
    false? invert ;

: lambda? ( obj -- obj bool )
    lambda-symbol tagged-list? ;

: lambda-parameters ( obj -- params )
    cdr car ;

: lambda-body ( obj -- body )
    cdr cdr ;

: application? ( obj -- obj bool )
    pair-type istype? ;

: operator ( obj -- operator )
    car ;

: operands ( obj -- operands )
    cdr ;

: nooperands? ( operands -- bool )
    nil objeq? ;

: first-operand ( operands -- operand )
    car ;

: rest-operands ( operands -- other-operands )
    cdr ;

: procedure-params ( proc -- params )
    drop pair-type car ;

: procedure-body ( proc -- body )
    drop pair-type cdr car ;

: procedure-env ( proc -- body )
    drop pair-type cdr cdr car ;

( Ensure terminating symbol arg name is handled
  specially to allow for variadic procedures. )
: flatten-proc-args ( argvals argnames -- argvals' argnames' )
    nil? if
        2over nil? false = if
            except-message: ." Too many arguments for compound procedure." recoverable-exception throw
        else
            2drop
        then
        exit
    then

    symbol-type istype? if
        nil cons
        2swap
        nil cons
        2swap
        exit
    then

    2over
    nil? if
        except-message: ." Too few arguments for compound procedure." recoverable-exception throw
    else
        cdr
    then

    2over cdr

    recurse ( argvals argnames argvals'' argnames'' )
    2rot car 2swap cons  ( argvals argvals'' argnames' )
    2rot car 2rot cons ( argnames' argvals' )
    2swap
;

\ }}}

\ ---- Analyze ---- {{{

: evaluate-eproc ( eproc env --- res )

    >R >R

    begin
        nil? invert
    while
        2dup car
        2swap cdr
    repeat
    
    2drop \ get rid of null

    R> R> 2swap

    \ Final element of eproc list is primitive procedure
    drop \ dump type signifier

    goto \ jump straight to primitive procedure (executor)
;

: self-evaluating-executor ( exp env -- exp )
    2drop ;

: analyze-self-evaluating ( exp --- eproc )
    ['] self-evaluating-executor primitive-proc-type
    nil cons cons
;

: quote-executor ( exp env -- exp )
    2drop ;

: analyze-quoted ( exp -- eproc )
    quote-body

    ['] quote-executor primitive-proc-type
    nil cons cons
;

: variable-executor ( var env -- val )
    lookup-var ;

: analyze-variable ( exp -- eproc )
    ['] variable-executor primitive-proc-type
    nil cons cons
;

: definition-executor ( var val-eproc env -- ok )
    2swap 2over ( var env val-eproc env )
    evaluate-eproc 2swap ( var val env )
    define-var
    ok-symbol
;

: analyze-definition ( exp -- eproc )
    2dup definition-var
    2swap definition-val analyze

    ['] definition-executor primitive-proc-type
    nil cons cons cons
;

: assignment-executor ( var val-eproc env -- ok )
    2swap 2over ( var env val-eproc env )
    evaluate-eproc 2swap ( var val env )
    set-var
    ok-symbol
;

: analyze-assignment ( exp -- eproc )
    2dup assignment-var
    2swap assignment-val analyze ( var val-eproc )

    ['] assignment-executor primitive-proc-type
    nil cons cons cons
;

: sequence-executor ( eproc-list env -- res )
    2swap

    begin
        2dup cdr ( env elist elist-rest)
        nil? invert
    while
        -2rot car 2over ( elist-rest env elist-head env )
        evaluate-eproc  ( elist-rest env head-res )
        2drop 2swap     ( env elist-rest )
    repeat

    2drop car 2swap
    ['] evaluate-eproc goto
;


: (analyze-sequence) ( explist -- eproc-list )
    nil? if exit then

    2dup car analyze
    2swap cdr recurse

    cons
;

: analyze-sequence ( explist -- eproc )
    (analyze-sequence)
    ['] sequence-executor primitive-proc-type
    nil cons cons
;


: macro-definition-executor  ( name params bproc env -- ok )
    make-macro ok-symbol
;

: analyze-macro-definition ( exp -- eproc )
    2dup macro-definition-name
    2swap 2dup macro-definition-params
    2swap macro-definition-body analyze-sequence

    ['] macro-definition-executor primitive-proc-type
    nil cons cons cons cons
;

: if-executor ( cproc aproc pproc env -- res )
    2swap 2over ( cproc aproc env pproc env -- res )
    evaluate-eproc

    true? if
        2swap 2drop
    else
        2rot 2drop
    then

    ['] evaluate-eproc goto
;

: analyze-if ( exp -- eproc )
    2dup if-consequent analyze
    2swap 2dup if-alternative analyze
    2swap if-predicate analyze

    ['] if-executor primitive-proc-type
    nil cons cons cons cons
;

: lambda-executor ( params bproc env -- res )
    make-procedure
    ( Although this is packaged up as a regular compound procedure,
      the "body" element contains an _eproc_ to be evaluated in an
      environment resulting from extending env with the parameter
      bindings. )
;

: analyze-lambda ( exp -- eproc )
    2dup lambda-parameters
    2swap lambda-body

    nil? if
        except-message: ." encountered lambda with an empty body." recoverable-exception throw
    then

    analyze-sequence

    ['] lambda-executor primitive-proc-type
    nil cons cons cons
;

: operand-eproc-list ( operands -- eprocs )
    nil? invert if
        2dup car analyze
        2swap cdr recurse
        cons
    then
;

: evaluate-operand-eprocs ( env aprocs -- vals )
    nil? if
        2swap 2drop
    else
        2over 2over car 2swap evaluate-eproc ( env aprocs thisval )
        -2rot cdr recurse ( thisval restvals )
        cons
    then
;

: apply ( vals proc )
    dup case
        primitive-proc-type of
            drop execute
        endof

        compound-proc-type of
                2dup procedure-body ( argvals proc bproc )
                -2rot 2dup procedure-params ( bproc argvals proc argnames )
                -2rot procedure-env ( bproc argnames argvals procenv )

                -2rot 2swap
                flatten-proc-args
                2swap 2rot

                extend-env ( bproc env )

               ['] evaluate-eproc goto
        endof

        continuation-type of
            2swap
            nil? if
                except-message: ." Continuations expect exactly 1 argument."
                recoverable-exception throw
            then

            2dup cdr

            nil? invert if
                except-message: ." Continuations expect exactly 1 argument."
                recoverable-exception throw
            then

            2drop car
                
            restore-continuation-with-arg
        endof

        except-message: ." object '" drop print ." ' not applicable." recoverable-exception throw
    endcase
;

: application-executor ( operator-proc arg-procs env -- res )
    2rot 2over ( aprocs env fproc env )
    evaluate-eproc ( aprocs env proc )

    -2rot 2swap ( proc env aprocs )
    evaluate-operand-eprocs ( proc vals )

    2swap ( vals proc )

    ['] apply goto
;

: analyze-application ( exp -- eproc )
    2dup operator analyze
    2swap operands operand-eproc-list

    ['] application-executor primitive-proc-type
    nil cons cons cons
;

:noname ( exp --- eproc )

    self-evaluating? if analyze-self-evaluating exit then

    quote? if analyze-quoted exit then
    
    variable? if analyze-variable exit then

    definition? if analyze-definition exit then

    assignment? if analyze-assignment exit then

    macro-definition? if analyze-macro-definition exit then

    if? if analyze-if exit then

    lambda? if analyze-lambda exit then

    application? if analyze-application exit then

    except-message: ." tried to analyze unknown expression type." recoverable-exception throw

; is analyze

\ }}}

\ ---- Macro Expansion ---- {{{

( Simply evaluates the given procedure with expbody as its argument. )
: macro-eval ( proc expbody -- result )
    2swap
    2dup procedure-body ( expbody proc bproc )
    -2rot 2dup procedure-params ( bproc expbody proc argnames )
    -2rot procedure-env ( bproc argnames expbody procenv )
    
    -2rot 2swap
    flatten-proc-args
    2swap 2rot

    extend-env ( bproc env )

    ['] evaluate-eproc goto
;

: expand-macro ( exp -- result )
    pair-type istype? invert if exit then

    2dup car symbol-type istype? invert if 2drop exit then

    lookup-macro nil? if 2drop exit then

    2over cdr macro-eval

    2dup no-match-symbol objeq? if
        2drop exit
    else
        2swap 2drop
    then

    R> drop ['] expand goto-deferred
;

: expand-definition ( exp -- result )
    define-symbol 2swap

    2dup definition-var
    2swap definition-val expand
    nil ( define var val' nil )

    cons cons cons ;

: expand-assignment ( exp -- result )
    set!-symbol 2swap

    2dup assignment-var
    2swap assignment-val expand
    nil ( define var val' nil )

    cons cons cons ;

: expand-list ( exp -- res )
    nil? if exit then

    2dup car expand
    2swap cdr recurse

    cons ;

: macro-definition-nameparams
    cdr car ;

: expand-define-macro ( exp -- res )
    define-macro-symbol 2swap
    2dup macro-definition-nameparams
    2swap macro-definition-body expand-list

    cons cons ;

: expand-lambda ( exp -- res )
    lambda-symbol 2swap
    2dup lambda-parameters
    2swap lambda-body expand-list

    cons cons ;

: expand-if ( exp -- res )
    if-symbol 2swap
    
    2dup if-predicate expand
    2swap 2dup if-consequent expand
    2swap if-alternative none? if
        2drop nil
    else
        expand nil cons
    then

    cons cons cons ;

: expand-application ( exp -- res )
    2dup operator expand
    2swap operands expand-list

    cons ;

:noname ( exp -- result )
    expand-macro

    self-evaluating? if exit then

    quote? if exit then

    definition? if expand-definition exit then

    assignment? if expand-assignment exit then

    macro-definition? if expand-define-macro exit then

    lambda? if expand-lambda exit then

    if? if expand-if exit then

    application? if expand-application exit then

; is expand

\ }}}

:noname ( exp env -- res )
    2swap expand analyze 2swap evaluate-eproc
; is eval

\ ---- Print ---- {{{

: printfixnum ( fixnum -- ) drop 0 .R ;

: printflonum ( flonum -- ) drop f. ;

: printratnum ( ratnum -- )
    drop pair-type 2dup
    car print ." /" cdr print
;

: printbool ( bool -- )
    drop if
        ." #t"
    else
        ." #f"
    then
;

: printchar ( charobj -- )
    drop
    case
        9 of ." #\tab" endof
        bl of ." #\space" endof
        '\n' of ." #\newline" endof
        
        dup ." #\" emit
    endcase
;

: (printstring) ( stringobj -- )
    nil? if 2drop exit then

    2dup car drop dup
    case
        '\n' of ." \n" drop endof
        [char] \ of ." \\" drop endof
        [char] " of [char] \ emit [char] " emit drop endof
        emit
    endcase

    cdr recurse
;
: printstring ( stringobj -- )
    [char] " emit
    (printstring)
    [char] " emit ;

: printsymbol ( symbolobj -- )
    nil-type istype? if 2drop exit then

    2dup car drop emit
    cdr recurse
;

: printnil ( nilobj -- )
    2drop ." ()" ;

: printpair ( pairobj -- )
    2dup
    car print
    cdr
    nil-type istype? if 2drop exit then
    pair-type istype? if space recurse exit then
    ."  . " print
;

: printprim ( primobj -- )
    2drop ." <primitive procedure>" ;

: printcomp ( primobj -- )
    2drop ." <compound procedure>" ;

: printcont ( primobj --)
    2drop ." <continuation>" ;

: printnone ( noneobj -- )
    2drop ." Unspecified return value" ;

: printport ( port -- )
    2drop ." <port>" ;

:noname ( obj -- )
    fixnum-type istype? if printfixnum exit then
    flonum-type istype? if printflonum exit then
    ratnum-type istype? if printratnum exit then
    boolean-type istype? if printbool exit then
    character-type istype? if printchar exit then
    string-type istype? if printstring exit then
    symbol-type istype? if printsymbol exit then
    nil-type istype? if printnil exit then
    pair-type istype? if ." (" printpair ." )" exit then
    primitive-proc-type istype? if printprim exit then
    compound-proc-type istype? if printcomp exit then
    continuation-type istype? if printcont exit then
    none-type istype? if printnone exit then
    port-type istype? if printport exit then

    except-message: ." tried to print object with unknown type." recoverable-exception throw
; is print

\ }}}

\ ---- Garbage Collection ---- {{{

( Notes on garbage collection:
  This is a mark-sweep garbage collector, invoked by cons.
  The roots of the object tree used by the marking routine 
  include all objects in the parameter stack, and several
  other fixed roots such as global-env, symbol-table, macro-table,
  and the console-i/o-port.

  NO OTHER OBJECTS WILL BE MARKED!

  This places implicit restrictions on when cons can be invoked.
  Invoking cons when live objects are stored on the return stack
  or in other variables than the above will result in possible
  memory corruption if the cons triggers the GC. )


: pairlike? ( obj -- obj bool )
    pair-type istype? if true exit then
    string-type istype? if true exit then
    symbol-type istype? if true exit then
    compound-proc-type istype? if true exit then
    port-type istype? if true exit then
    continuation-type istype? if true exit then

    false
;

: pairlike-marked? ( obj -- obj bool )
    over nextfrees + @ 0=
;

: mark-pairlike ( obj -- obj )
        over nextfrees + 0 swap !
;

: gc-unmark ( -- )
    scheme-memsize 0 do
        1 nextfrees i + !
    loop
;

: gc-mark-obj ( obj -- )

    pairlike? invert if 2drop exit then
    pairlike-marked? if 2drop exit then

    mark-pairlike

    drop pair-type 2dup

    car recurse
    cdr recurse
;

: gc-sweep
    scheme-memsize nextfree !
    0 scheme-memsize 1- do
        nextfrees i + @ 0<> if
            nextfree @ nextfrees i + !
            i nextfree !
        then
    -1 +loop
;

\ Following a GC, this gives the amount of free memory
: gc-count-marked
    0
    scheme-memsize 0 do
        nextfrees i + @ 0= if 1+ then
    loop
;

\ Debugging word - helps spot memory that is retained
: gc-zero-unmarked
    scheme-memsize 0 do
        nextfrees i + @ 0<> if
            0 car-cells i + !
            0 cdr-cells i + !
        then
    loop
;

:noname
    \ ." GC! "

    gc-unmark

    symbol-table obj@ gc-mark-obj
    macro-table obj@ gc-mark-obj
    console-i/o-port obj@ gc-mark-obj
    global-env obj@ gc-mark-obj

    depth object-stack-base @ do
        PSP0 i + 1 + @
        PSP0 i + 2 + @

        gc-mark-obj
    2 +loop

    gc-sweep

    \ ." (" gc-count-marked . ." pairs marked as used.)" cr
; is collect-garbage

\ }}}

\ ---- Loading files ---- {{{

: load ( addr n -- finalResult )
    open-input-file

    empty-parse-str

    ok-symbol ( port res )

    begin
        \ DEBUG
        \ bold fg blue ." READ from " 2over drop . ." ==> " reset-term

        2over read-port ( port res obj )

        \ DEBUG
        \ 2dup print cr

        2dup EOF character-type objeq? if
            2drop 2swap close-port
            exit
        then

        2swap 2drop ( port obj )

        global-env obj@ eval ( port res )
    again
;

\ }}}

\ ---- Standard Library ---- {{{

    include scheme-primitives.4th

    init-object-stack-base
    s" scheme-library.scm" load 2drop
    
\ }}}

\ ---- REPL ----

( REPL calls REPL-BODY in a loop until repl-body returns true. )
: repl-body ( -- bool )
    cr bold fg green ." > " reset-term

    read-console

    2dup EOF character-type objeq? if
        2drop
        bold fg blue ." Moriturus te saluto." reset-term cr
        true exit
    then

    global-env obj@ eval

    fg cyan ." ; " print reset-term

    false
;

: repl
    empty-parse-str

    init-object-stack-base

    \ Display welcome message
    welcome-symbol nil cons global-env obj@ eval 2drop

    begin
        ['] repl-body catch
        case
            recoverable-exception of false endof
            unrecoverable-exception of true endof

            throw false
        endcase
    until
;

forth definitions

\ vim:fdm=marker