X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?p=scheme.forth.jl.git;a=blobdiff_plain;f=scheme.4th;h=f8dd0899d0e02aac9094648a03be84f1f10ee6f6;hp=8d9c97a8938a865d92ddf9326379fb027337ec3a;hb=3eaf389aa81bcfbf8dd64c89520925413d5c2390;hpb=bc4c866824b12208394e0ca8d6468ed8cd5c49a8

diff --git a/scheme.4th b/scheme.4th
index 8d9c97a..f8dd089 100644
--- a/scheme.4th
+++ b/scheme.4th
@@ -1,194 +1,1530 @@
-\ Scheme interpreter
+vocabulary scheme
+scheme definitions
+
+include term-colours.4th
+include defer-is.4th
+include catch-throw.4th
+include float.4th
+
+include debugging.4th
+
+defer read
+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 realnum-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 fileport-type
+: istype? ( obj type -- obj bool )
+    over = ;
+
+\ }}}
+
+\ ---- Exceptions ---- {{{
+
+variable nextexception
+1 nextexception !
+: make-exception 
+    create nextexception @ ,
+    1 nextexception +!
+    does> @ ;
+
+make-exception recoverable-exception
+make-exception unrecoverable-exception
+
+: display-exception-msg ( addr count -- )
+    bold fg red
+    ." Exception: "
+    type
+    reset-term ;
+
+: throw" immediate 
+    [compile] s"
+
+    ['] rot , ['] dup ,
+
+    [compile] if
+        ['] -rot ,
+        ['] display-exception-msg ,
+    [compile] then
+
+    ['] throw ,
+;
+
+\ }}}
+
+\ ---- List-structured memory ---- {{{
+
+10000 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
+        unrecoverable-exception throw s" Out of memory!"
+    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 + !
+;
+
+: 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>
+;
+
+\ }}}
+
+\ ---- Port I/O ----  {{{
+
+: fileport>fid ( fileport -- fid )
+    drop ;
+
+: fid>fileport ( fid -- fileport )
+    fileport-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 fileport-type console-i/o-port obj!
+
+objvar current-input-port
+console-i/o-port obj@ current-input-port obj!
+
+: read-port ( fileport -- obj )
+    current-input-port obj!
+    read ;
+
+: read-console ( -- obj )
+    console-i/o-port obj@ read-port ;
+
+\ }}}
+
+\ ---- 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 begin             begin-symbol
+
+\ }}}
+
+\ ---- Environments ---- {{{
+
+: enclosing-env ( env -- env )
+    cdr ;
+
+: first-frame ( env -- frame )
+    car ;
+
+: make-frame ( vars vals -- frame )
+    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 )
+    >R >R
+    make-frame
+    R> R>
+    cons
+;
+
+objvar vars
+objvar vals
+
+: get-vars-vals-frame ( var frame -- bool )
+    2dup frame-vars vars obj!
+    frame-vals vals obj!
+
+    begin
+        vars obj@ nil objeq? false =
+    while
+        2dup vars obj@ car objeq? if
+            2drop true
+            exit
+        then
+
+        vars obj@ cdr vars obj!
+        vals obj@ cdr vals obj!
+    repeat
+
+    2drop false
+;
+
+: get-vars-vals ( var env -- vars? vals? bool )
+
+    begin
+        nil? false =
+    while
+        2over 2over first-frame
+        get-vars-vals-frame if
+            2drop 2drop
+            vars obj@ vals obj@ true
+            exit
+        then
+
+        enclosing-env
+    repeat
+
+    2drop 2drop
+    false
+;
+
+hide vars
+hide vals
+
+: lookup-var ( var env -- val )
+    get-vars-vals if
+        2swap 2drop car
+    else
+        recoverable-exception throw" Tried to read unbound variable."
+    then
+;
+
+: set-var ( var val env -- )
+    >R >R 2swap R> R> ( val var env )
+    get-vars-vals if
+        2swap 2drop ( val vals )
+        set-car!
+    else
+        recoverable-exception throw" Tried to set unbound variable."
+    then
+;
+
+objvar env
+
+: define-var ( var val env -- )
+    env obj! 
+
+    2over env obj@ ( var val var env )
+    get-vars-vals if
+        2swap 2drop ( var val vals )
+        set-car!
+        2drop
+    else
+        env obj@
+        first-frame ( var val frame )
+        add-binding
+    then
+;
+
+hide env
+
+: 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!
+
+\ }}}
+
+\ ---- Primitives ---- {{{
+
+: make-primitive ( cfa -- )
+    bl word
+    count
+
+    \ 2dup ." Defining primitive " type ." ..." cr
+
+    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
+            recoverable-exception throw" Too many arguments for primitive procedure."
+        then
+    else
+        -rot nil? if
+            recoverable-exception throw" Too few arguments for primitive procedure."
+        then
+        
+        cdr rot 1- recurse
+    then
+;
+
+: arg-type-error
+            bold fg red ." Incorrect argument type." reset-term cr
+            abort
+;
+
+: ensure-arg-type ( arg type -- arg )
+    istype? false = if
+        recoverable-exception throw" Incorrect argument type for primitive procedure."
+    then
+;
+
+
+\ }}}
+
+\ ---- Macros ---- {{{
+
+objvar macro-table
+
+( Look up macro in macro table. Returns nil if
+  no macro is found. )
+: lookup-macro ( name_symbol -- proc )
+    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 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
+;
+
+: realnum? ( -- 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
+;
+
+: 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 ( -- num-atom )
+    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
+;
+
+: readrealnum ( -- realnum )
+
+    \ Remember that at this point we're guaranteed to
+    \ have a parsable real on this line.
+
+    parse-str parse-idx @ +
+
+    begin delim? false = while
+            inc-parse-idx
+    repeat
+
+    parse-str parse-idx @ + over -
+
+    float-parse
+
+    realnum-type
+;
+
+: 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 )
+    nextchar [char] " = if
+        inc-parse-idx
+
+        delim? false = if
+            bold fg red
+            ." No delimiter following right double quote. Aborting." cr
+            reset-term abort
+        then
+
+        dec-parse-idx
+
+        0 nil-type exit
+    then
+
+    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
+
+    recurse
+
+    cons
+;
+
+: 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
+
+    realnum? if
+        readrealnum
+        exit
+    then
+
+    boolean? if
+        readbool
+        exit
+    then
+
+    character? if
+        readchar
+        exit
+    then
+
+    string? if
+        inc-parse-idx
+
+        readstring
+        drop string-type
+
+        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
+
+    \ 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
+
+\ }}}
+
+\ ---- Eval ---- {{{
+
+: self-evaluating? ( obj -- obj bool )
+    boolean-type istype? if true exit then
+    fixnum-type istype? if true exit then
+    realnum-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 ;
+
+: quasiquote? ( obj -- obj bool )
+    quasiquote-symbol tagged-list? ;
+
+: unquote? ( obj -- obj bool )
+    unquote-symbol tagged-list? ;
+
+: unquote-splicing? ( obj -- obj bool )
+    unquote-splicing-symbol tagged-list? ;
+
+: eval-unquote ( env obj -- res )
+    cdr ( env args )
+
+    nil? if
+        recoverable-exception throw" no arguments to unquote."
+    then
+
+    2dup cdr
+    nil? false = if
+        recoverable-exception throw" too many arguments to unquote."
+    then
+
+    2drop car 2swap eval
+;
+
+( Create a new list from elements of l1 consed on to l2 )
+: join-lists ( l2 l1 -- l3 )
+    nil? if 2drop exit then
+
+    2dup car
+    -2rot cdr
+    recurse cons
+;
+
+defer eval-quasiquote-item
+: eval-quasiquote-pair ( env obj -- res )
+    2over 2over ( env obj env obj )
+
+    cdr eval-quasiquote-item
+
+    -2rot car ( cdritem env objcar )
+
+    unquote-splicing? if
+        eval-unquote ( cdritems caritem )
+
+        2swap nil? if
+            2drop
+        else
+            2swap join-lists
+        then
+    else
+        eval-quasiquote-item ( cdritems caritem )
+        2swap cons
+    then
+
+;
+
+:noname ( env obj )
+    nil? if
+        2swap 2drop exit
+    then
 
-vocabulary scheme
-scheme definitions
+    unquote? if
+        eval-unquote exit
+    then
 
-include term-colours.4th
+    pair-type istype? if
+        eval-quasiquote-pair exit
+    then
 
-0 constant number-type
-1 constant boolean-type
-2 constant character-type
-: istype? ( obj -- obj b )
-    over = ;
+    2swap 2drop
+; is eval-quasiquote-item
 
-\ ---- Read ----
+: eval-quasiquote ( obj env -- res )
+    2swap cdr ( env args )
 
-variable parse-idx
-variable dummy-parse-idx
+    nil? if
+        recoverable-exception throw" no arguments to quasiquote."
+    then
 
-: inc-parse-idx
-    1 parse-idx +! ;
+    2dup cdr ( env args args-cdr )
+    nil? false = if
+        recoverable-exception throw" too many arguments to quasiquote."
+    then
 
-: dec-parse-idx
-    1 parse-idx -! ;
+    2drop car ( env arg )
+
+    eval-quasiquote-item
+;
 
-: store-parse-idx
-    parse-idx @ dummy-parse-idx !  ;
+: variable? ( obj -- obj bool )
+    symbol-type istype? ;
 
-: restore-parse-idx
-    dummy-parse-idx @ parse-idx !  ;
+: definition? ( obj -- obj bool )
+    define-symbol tagged-list? ;
 
-variable parse-str
+: make-lambda ( params body -- lambda-exp )
+    lambda-symbol -2rot cons cons ;
 
-: charavailable? ( -- bool )
-    parse-str @ @ parse-idx @ >
+( Handles iterative expansion of defines in
+  terms of nested lambdas. Most Schemes only
+  handle one iteration of expansion! )
+: definition-var-val ( obj -- var val )
+
+    cdr 2dup cdr 2swap car ( val var )
+
+    begin
+        symbol-type istype? false =
+    while
+        2dup cdr 2swap car ( val formals var' )
+        -2rot 2swap ( var' formals val )
+        make-lambda nil cons ( var' val' )
+        2swap ( val' var' )
+    repeat
+
+    2swap car
 ;
 
-: nextchar ( -- char )
-    charavailable? if
-        parse-str @ 1+ parse-idx @ + @
-    else
-        0
-    then
+: eval-definition ( obj env -- res )
+    2dup 2rot ( env env obj )
+    definition-var-val ( env env var val )
+    2rot eval  ( env var val )
+
+    2rot ( var val env )
+    define-var
+
+    ok-symbol
 ;
 
-: whitespace? ( -- bool )
-    nextchar BL = 
-    nextchar '\n' = or
+: assignment? ( obj -- obj bool )
+    set!-symbol tagged-list? ;
+
+: assignment-var ( obj -- var )
+    cdr car ;
+    
+: assignment-val ( obj -- val )
+    cdr cdr car ;
+
+: eval-assignment ( obj env -- res )
+    2swap 
+    2over 2over ( env obj env obj )
+    assignment-val 2swap ( env obj valexp env )
+    eval  ( env obj val )
+    
+    2swap assignment-var 2swap ( env var val )
+
+    2rot ( var val env )
+    set-var
+
+    ok-symbol
 ;
 
-: delim? ( -- bool )
-    whitespace?
-    nextchar [char] ( = or
-    nextchar [char] ) = or
+: 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 ;
+
+objvar env
+: eval-define-macro ( obj env -- res )
+    env obj!
+
+    2dup macro-definition-name 2swap ( name obj )
+    2dup macro-definition-params 2swap ( name params obj )
+    macro-definition-body ( name params body )
+
+    env obj@ ( name params body env )
+
+    make-macro
+
+    ok-symbol
 ;
+hide env
+
+: 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 ;
+
+: begin? ( obj -- obj bool )
+    begin-symbol tagged-list? ;
+
+: begin-actions ( obj -- actions )
+    cdr ;
+
+: eval-sequence ( explist env -- finalexp env )
+    ( Evaluates all bar the final expressions in
+      an an expression list. The final expression
+      is returned to allow for tail optimization. )
+
+    2swap ( env explist )
+
+    \ Abort on empty list
+    nil? if
+        2drop none
+        2swap exit
+    then
 
-: eatspaces
     begin
-        whitespace?
+        2dup cdr ( env explist nextexplist )
+        nil? false =
     while
-        inc-parse-idx
+        -2rot car 2over ( nextexplist env exp env )
+        eval
+        2drop \ discard result
+        2swap ( env nextexplist )
     repeat
+
+    2drop car 2swap ( finalexp env )
 ;
 
-: digit? ( -- bool )
-    nextchar [char] 0 >=
-    nextchar [char] 9 <=
-    and ;
+: application? ( obj -- obj bool )
+    pair-type istype? ;
 
-: minus? ( -- bool )
-    nextchar [char] - = ;
+: operator ( obj -- operator )
+    car ;
 
-: number? ( -- bool )
-    digit? minus? or false = if
-        false
-        exit
-    then
+: operands ( obj -- operands )
+    cdr ;
 
-    store-parse-idx
-    inc-parse-idx
+: nooperands? ( operands -- bool )
+    nil objeq? ;
 
-    begin digit? while
-        inc-parse-idx
-    repeat
+: first-operand ( operands -- operand )
+    car ;
 
-    delim? charavailable? false = or if
-        restore-parse-idx
-        true
+: rest-operands ( operands -- other-operands )
+    cdr ;
+
+: list-of-vals ( args env -- vals )
+    2swap
+
+    2dup nooperands? if
+        2swap 2drop
     else
-        restore-parse-idx
-        false
+        2over 2over first-operand 2swap eval
+        -2rot rest-operands 2swap recurse
+        cons
     then
 ;
 
-: boolean? ( -- bool )
-    nextchar [char] # <> if false exit then
+: procedure-params ( proc -- params )
+    drop pair-type car ;
 
-    store-parse-idx
-    inc-parse-idx
+: procedure-body ( proc -- body )
+    drop pair-type cdr car ;
 
-    nextchar [char] t <>
-    nextchar [char] f <>
-    and if restore-parse-idx false exit then
+: procedure-env ( proc -- body )
+    drop pair-type cdr cdr car ;
 
-    restore-parse-idx
-    true
-;
+( 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
+            recoverable-exception throw" Too many arguments for compound procedure."
+        else
+            2drop
+        then
+        exit
+    then
 
-: character? ( -- bool )
-    nextchar [char] # <> if false exit then
+    symbol-type istype? if
+        nil cons
+        2swap
+        nil cons
+        2swap
+        exit
+    then
 
-    store-parse-idx
-    inc-parse-idx
+    2over
+    nil? if
+        recoverable-exception throw" Too few arguments for compound procedure."
+    else
+        cdr
+    then
 
-    nextchar [char] \ <> if restore-parse-idx false exit then
+    2over cdr
 
-    inc-parse-idx
+    recurse ( argvals argnames argvals'' argnames'' )
+    2rot car 2swap cons  ( argvals argvals'' argnames' )
+    2rot car 2rot cons ( argnames' argvals' )
+    2swap
+;
 
-    charavailable? false = if restore-parse-idx false exit then
+: apply ( proc argvals -- result )
+        2swap dup case
+            primitive-proc-type of
+                drop execute     
+            endof
 
-    restore-parse-idx true
-;
+            compound-proc-type of
+                2dup procedure-body ( argvals proc body )
+                -2rot 2dup procedure-params ( body argvals proc argnames )
+                -2rot procedure-env ( body argnames argvals procenv )
 
-: readnum ( -- num-atom )
-    minus? dup if
-        inc-parse-idx
-    then
+                -2rot 2swap
+                flatten-proc-args
+                2swap 2rot
 
-    0
+                extend-env ( body env )
 
-    begin digit? while
-        10 * nextchar [char] 0 - +
-        inc-parse-idx
-    repeat
+                eval-sequence
 
-    swap if negate then
+                R> drop ['] eval goto-deferred  \ Tail call optimization
+            endof
 
-    number-type
+            recoverable-exception throw" Object not applicable."
+        endcase
 ;
 
-: readbool ( -- bool-atom )
-    inc-parse-idx
+( Simply evaluates the given procedure with expbody as its argument. )
+: macro-expand ( proc expbody -- result )
+    2swap
+    2dup procedure-body ( expbody proc procbody )
+    -2rot 2dup procedure-params ( procbody expbody proc argnames )
+    -2rot procedure-env ( procbody argnames expbody procenv )
     
-    nextchar [char] f = if
-        false
-    else
-        true
-    then
+    -2rot 2swap
+    flatten-proc-args
+    2swap 2rot
 
-    boolean-type
+    extend-env eval-sequence eval
 ;
 
-\ Parse a counted string into a scheme expression
-: read ( -- obj )
+:noname ( obj env -- result )
+    2swap
 
-    eatspaces
+    self-evaluating? if
+        2swap 2drop
+        exit
+    then
 
-    number? if
-        readnum
+    quote? if
+        quote-body
+        2swap 2drop
         exit
     then
 
-    boolean? if
-        readbool
+    quasiquote? if
+        2swap eval-quasiquote
         exit
     then
 
-    bold fg red ." Error parsing string starting at character '"
-    nextchar emit
-    ." '. Aborting." reset-term cr
-    abort
-;
+    variable? if
+        2swap lookup-var
+        exit
+    then
 
-\ ---- Eval ----
+    definition? if
+        2swap eval-definition
+        exit
+    then
 
-: self-evaluating? ( obj -- obj bool )
-    number-type istype? if true exit then
-    boolean-type istype? if true exit then
-    false ;
+    assignment? if
+        2swap eval-assignment
+        exit
+    then
 
-: eval
-    self-evaluating? if
+    macro-definition? if
+        2swap eval-define-macro
         exit
     then
 
-    bold fg red ." Error evaluating expression - unrecognized type. Aborting." reset-term cr
-    abort
-;
+    if? if
+        2over 2over
+        if-predicate
+        2swap eval 
+
+        true? if
+            if-consequent
+        else
+            if-alternative
+        then
+
+        2swap
+        ['] eval goto-deferred
+    then
+
+    lambda? if
+        2dup lambda-parameters
+        2swap lambda-body
+        2rot make-procedure
+        exit
+    then
+
+    begin? if
+        begin-actions 2swap
+        eval-sequence
+        ['] eval goto-deferred
+    then
+
+    application? if
+
+        2over 2over ( env exp env exp )
+        operator ( env exp env opname )
+
+        2dup lookup-macro nil? false = if
+             \ Macro function evaluation
+
+            ( env exp env opname mproc )
+            2swap 2drop -2rot 2drop cdr ( env mproc body )
+
+            macro-expand
+
+            2swap
+            ['] eval goto-deferred
+        else
+           \ Regular function application
+
+            2drop ( env exp env opname )
+
+            2swap eval ( env exp proc )
+
+            -2rot ( proc env exp )
+            operands 2swap ( proc operands env )
+            list-of-vals ( proc argvals )
+
+            apply
+            exit
+        then
+    then
+
+    recoverable-exception throw" Tried to evaluate object with unknown type."
+; is eval
 
-\ ---- Print ----
+\ }}}
 
-: printnum ( numobj -- ) drop . ;
+\ ---- Print ---- {{{
+
+: printfixnum ( fixnumobj -- ) drop 0 .R ;
+
+: printrealnum ( realnumobj -- ) drop float-print ;
 
 : printbool ( numobj -- )
     drop if
@@ -198,45 +1534,279 @@ variable parse-str
     then
 ;
 
-: print ( obj -- )
-    ." ; "
-    number-type istype? if ." => " printnum exit then
-    boolean-type istype? if ." => " printbool exit then
+: printchar ( charobj -- )
+    drop
+    case
+        9 of ." #\tab" endof
+        bl of ." #\space" endof
+        '\n' of ." #\newline" endof
+        
+        dup ." #\" emit
+    endcase
 ;
 
-\ ---- REPL ----
+: (printstring) ( stringobj -- )
+    nil? if 2drop exit then
 
-create repl-buffer 161 allot
-repl-buffer parse-str !
+    2dup car drop dup
+    case
+        '\n' of ." \n" drop endof
+        [char] \ of ." \\" drop endof
+        [char] " of [char] \ emit [char] " emit drop endof
+        emit
+    endcase
 
-: getline
-    repl-buffer 1+ 160 expect span @ repl-buffer ! ;
+    cdr recurse
+;
+: printstring ( stringobj -- )
+    [char] " emit
+    (printstring)
+    [char] " emit ;
 
-: eof?
-    repl-buffer @ 0= if false exit then
-    repl-buffer 1+ @ 4 <> if false exit then
-    true ;
+: printsymbol ( symbolobj -- )
+    nil-type istype? if 2drop exit then
 
-: repl
-    cr ." Welcome to scheme.forth.jl!" cr
-       ." Use Ctrl-D to exit." cr
+    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>" ;
+
+: printnone ( noneobj -- )
+    2drop ." Unspecified return value" ;
+
+: printport ( port -- )
+    2drop ." <port>" ;
+
+:noname ( obj -- )
+    fixnum-type istype? if printfixnum exit then
+    realnum-type istype? if printrealnum 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
+    none-type istype? if printnone exit then
+
+    recoverable-exception throw" Tried to print object with unknown type."
+; is print
+
+\ }}}
+
+\ ---- Garbage Collection ---- {{{
+
+variable gc-enabled
+false gc-enabled !
+
+variable gc-stack-depth
+
+: enable-gc
+    depth gc-stack-depth !
+    true gc-enabled ! ;
+
+: disable-gc
+    false gc-enabled ! ;
+
+: gc-enabled?
+    gc-enabled @ ;
+
+: 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
+
+    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
+    global-env obj@ gc-mark-obj
+
+    depth gc-stack-depth @ 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 ---- {{{
+
+: charlist>cstr ( charlist addr -- n )
+
+    dup 2swap ( origaddr addr charlist )
+
+    begin 
+        nil? false =
+    while
+        2dup cdr 2swap car 
+        drop ( origaddr addr charlist char )
+        -rot 2swap ( origaddr charlist addr char )
+        over !
+        1+ -rot ( origaddr nextaddr charlist )
+    repeat
+
+    2drop ( origaddr finaladdr ) 
+    swap -
+;
+
+: load ( addr n -- finalResult )
+    open-input-file
+
+    empty-parse-str
+
+    ok-symbol ( port res )
 
     begin
-        cr bold fg green ." > " reset-term
-        getline
+        2over read-port ( port res obj )
 
-        eof? if
-            cr bold fg blue ." Moriturus te saluto." reset-term
+        2dup EOF character-type objeq? if
+            2drop 2swap close-port
             exit
         then
 
-        repl-buffer @ 0> if
-            0 parse-idx !
-            read
-            eval
-            fg cyan print reset-term
-        then
+        2swap 2drop ( port obj )
+
+        global-env obj@ eval ( port res )
     again
 ;
 
+\ }}}
+
+\ ---- Standard Library ---- {{{
+
+    include scheme-primitives.4th
+
+    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
+    cr ." Welcome to scheme.forth.jl!" cr
+       ." Use Ctrl-D to exit." cr
+
+    empty-parse-str
+
+    enable-gc
+
+    begin
+        ['] repl-body catch
+        case
+            recoverable-exception of false endof
+            unrecoverable-exception of true endof
+
+            throw false
+        endcase
+    until
+;
+
 forth definitions
+
+\ vim:fdm=marker