X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=scheme.4th;h=9d86461accd46f972012b8663bbc2c79a32fbfad;hb=d1107557350ae9101bfa387dd2af2cad541193cc;hp=5fe8b3eb07663763be2ee6a3f9a0b4ca06253f9b;hpb=96099b1d09aae7cf167efca9fd04406750eb7157;p=scheme.forth.jl.git

diff --git a/scheme.4th b/scheme.4th
index 5fe8b3e..9d86461 100644
--- a/scheme.4th
+++ b/scheme.4th
@@ -1,179 +1,1075 @@
-\ Scheme interpreter
-
 vocabulary scheme
 scheme definitions
 
-\ Cons cell memory
-1000 constant memsize
-create car memsize allot
-create cdr memsize allot
-create types memsize allot
+include term-colours.4th
+include defer-is.4th
+
+\ ------ Types ------
+
+0 constant fixnum-type
+1 constant boolean-type
+2 constant character-type
+3 constant string-type
+4 constant nil-type
+5 constant pair-type
+6 constant symbol-type
+7 constant primitive-type
+: istype? ( obj type -- obj bool )
+    over = ;
 
-0 constant symbol-type
-1 constant int-type
-2 constant list-type
-3 constant bool-type
+\ ------ Cons cell memory ------ {{{
+
+1000 constant N
+create car-cells N allot
+create car-type-cells N allot
+create cdr-cells N allot
+create cdr-type-cells N allot
 
 variable nextfree
 0 nextfree !
 
-: stack
-    create here 1+ , allot ;
+: cons ( car-obj cdr-obj -- pair-obj )
+    cdr-type-cells nextfree @ + !
+    cdr-cells nextfree @ + !
+    car-type-cells nextfree @ + !
+    car-cells nextfree @ + !
 
+    nextfree @ pair-type
 
-: push ( st v -- )
-    over @ !
-    1 swap +!
+    1 nextfree +!
 ;
 
-: pop ( st -- v )
-    dup @       ( s0 sp )
-    1-          ( so sp' )
+: car ( pair-obj -- car-obj )
+    drop
+    dup car-cells + @ swap
+    car-type-cells + @
+;
 
-    2dup = abort" Stack underflow."
-    
-    dup @       ( s0 sp' v )
-    -rot swap   ( v sp' s0 )
-    !
+: cdr ( pair-obj -- car-obj )
+    drop
+    dup cdr-cells + @ swap
+    cdr-type-cells + @
 ;
 
-100 stack parse-stack 
-variable parse-idx
-variable parse-str
+: 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 + !
+;
+
+: caar car car ;
+: cadr cdr car ;
+: cdar car cdr ;
+: cddr cdr cdr ;
 
+: nil 0 nil-type ;
+: nil? nil-type istype? ;
 
-: inc-parse-idx parse-idx +! ;
-: dec-parse-idx parse-idx -! ;
+: objvar create nil swap , , ;
 
-: ?charavailable ( -- bool )
-    parse-str @ @ parse-idx @ >
+: value@ ( objvar -- val ) @ ;
+: type@ ( objvar -- type ) 1+ @ ;
+: value! ( newval objvar -- ) ! ;
+: type! ( newtype objvar -- ) 1+ ! ;
+: setobj ( newobj objvar -- ) dup rot swap 1+ ! ! ; 
+: fetchobj ( 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
 ;
 
-: nextchar ( -- char )
-    ?charavailable if
-        parse-str @ 1+ parse-idx @ + @
+: -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>
+;
+
+\ }}}
+
+\ ---- Pre-defined symbols ---- {{{
+
+objvar symbol-table
+
+: duplicate-charlist ( charlist -- copy )
+    2dup nil objeq? 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
-        0
+        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
 ;
 
-: ?whitespace ( -- bool )
-    nextchar BL = 
-    nextchar '\n' = or
+: charlist>symbol ( charlist -- symbol-obj )
+
+    symbol-table fetchobj
+
+    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 fetchobj cons
+    symbol-table setobj
+;
+
+
+: (create-symbol) ( addr n -- symbol-obj )
+    dup 0= if
+        2drop nil
+    else
+        2dup drop @ character-type 2swap
+        swap 1+ swap 1-
+        recurse
+
+        cons
+    then
+;
+
+: create-symbol ( -- )
+    bl word
+    count
+
+    (create-symbol)
+    drop symbol-type
+
+    2dup
+
+    symbol-table fetchobj
+    cons
+    symbol-table setobj
+
+    create swap , ,
+    does> dup @ swap 1+ @
+;
+
+create-symbol quote     quote-symbol
+create-symbol define    define-symbol
+create-symbol set!      set!-symbol
+create-symbol ok        ok-symbol
+create-symbol if        if-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 setobj
+    frame-vals vals setobj
+
+    begin
+        vars fetchobj nil objeq? false =
+    while
+        2dup vars fetchobj car objeq? if
+            2drop true
+            exit
+        then
+
+        vars fetchobj cdr vars setobj
+        vals fetchobj cdr vals setobj
+    repeat
+
+    2drop false
+;
+
+: get-vars-vals ( var env -- vars? vals? bool )
+
+    begin
+        2dup nil objeq? false =
+    while
+        2over 2over first-frame
+        get-vars-vals-frame if
+            2drop 2drop
+            vars fetchobj vals fetchobj 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
+        bold fg red ." Tried to read unbound variable." reset-term cr abort
+    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
+        bold fg red ." Tried to set unbound variable." reset-term cr abort
+    then
+;
+
+objvar env
+
+: define-var ( var val env -- )
+    env setobj 
+
+    2over env fetchobj ( var val var env )
+    get-vars-vals if
+        2swap 2drop ( var val vals )
+        set-car!
+        2drop
+    else
+        env fetchobj
+        first-frame ( var val frame )
+        add-binding
+    then
+;
+
+hide env
+
+objvar global-env
+nil nil nil extend-env
+global-env setobj
+
+\ }}}
+
+\ ---- Primitives ---- {{{
+
+: make-primitive ( cfa -- )
+    bl word
+    count
+
+    (create-symbol)
+    drop symbol-type
+    
+    2dup
+
+    symbol-table fetchobj
+    cons
+    symbol-table setobj
+
+    rot primitive-type ( var prim )
+    global-env fetchobj define-var
+;
+
+: arg-count-error
+            bold fg red ." Incorrect argument count." reset-term cr
+            abort
 ;
 
-: ?delim ( -- bool )
-    ?whitespace
+: ensure-arg-count ( args n -- )
+    dup 0= if
+        drop nil objeq? false = if
+            arg-count-error
+        then
+    else
+        -rot 2dup nil objeq? if
+            arg-count-error
+        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
+        arg-type-error
+    then
+;
+
+include scheme-primitives.4th
+
+\ }}}
+
+\ ---- Read ---- {{{
+
+defer 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 +! ;
+
+: empty-parse-str
+    0 parse-str-span !
+    0 parse-idx ! ;
+
+: getline
+    parse-str 160 expect cr
+    span @ parse-str-span !
+    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 @ + @ ;
+
+: whitespace? ( -- bool )
+    nextchar BL = 
+    nextchar '\n' = or ;
+
+: eof? ( -- bool )
+    nextchar 4 = ;
+
+: 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
-        ?whitespace
+        dup whitespace? or commentstart? or
     while
-            1 parse-idx +!
+        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
 ;
 
-: parsebool
+: digit? ( -- bool )
+    nextchar [char] 0 >=
+    nextchar [char] 9 <=
+    and ;
 
-    nextchar emit cr
-    trace
+: minus? ( -- bool )
+    nextchar [char] - = ;
 
-    false
-    nextchar [char] # <> if exit then
+: plus? ( -- bool )
+    nextchar [char] + = ;
 
-    1 inc-parse-idx
+: fixnum? ( -- bool )
+    minus? plus? or if
+        inc-parse-idx
 
-    nextchar dup [char] t = swap [char] f = or
-    not if
-        1 dec-parse-idx
-        exit
+        delim? if
+            dec-parse-idx
+            false exit
+        else
+            dec-parse-idx
+        then
+    else
+        digit? false = if
+            false exit
+        then
     then
 
-    1 inc-parse-idx
+    push-parse-idx
+    inc-parse-idx
 
-    ?delim not if
-        2 dec-parse-idx
-        exit
+    begin digit? while
+        inc-parse-idx
+    repeat
+
+    delim? if
+        pop-parse-idx
+        true
+    else
+        pop-parse-idx
+        false
     then
 ;
 
-: parsetoken
+: 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] " = ;
+
+: readnum ( -- 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
+;
+
+: readbool ( -- bool-atom )
+    inc-parse-idx
+    
+    nextchar [char] f = if
+        false
+    else
+        true
+    then
+
+    inc-parse-idx
+
+    boolean-type
+;
+
+: readchar ( -- char-atom )
+    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
 
-    \ Parens
+    fixnum? if
+        readnum
+        exit
+    then
 
-    nextchar [char] ( = if
-        \ todo
+    boolean? if
+        readbool
         exit
     then
 
-    nextchar [char] ) = if
-        \ todo
+    character? if
+        readchar
         exit
     then
 
-    parsebool if
+    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
-    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
+
+    eof? if
+        bold fg blue ." Moriturus te saluto." reset-term ."  ok" cr
+        quit
+    then
+
+    \ Anything else is parsed as a symbol
+    readsymbol charlist>symbol
+
+; is read
+
+\ }}}
+
+\ ---- Eval ---- {{{
+
+defer eval
+
+: self-evaluating? ( obj -- obj bool )
+    boolean-type istype? if true exit then
+    fixnum-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
+
+    false
 ;
 
-\ Parse a counted string into a scheme expression
-: parseexp ( straddr n -- exp )
-    0 parse-idx !
+: tagged-list? ( obj tag-obj -- obj bool )
+    2over 
+    pair-type istype? false = if
+        2drop 2drop false
+    else
+        car objeq?
+    then ;
 
-    begin
-        parsetoken
-    nextchar 0 =
-    until
+: quote? ( obj -- obj bool )
+    quote-symbol tagged-list?  ;
+
+: quote-body ( quote-obj -- quote-body-obj )
+    cadr ;
+
+: 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 ;
+
+: eval-definition ( obj env -- res )
+    2swap 
+    2over 2over ( env obj env obj )
+    definition-val 2swap ( env obj valexp env )
+    eval  ( env obj val )
+    
+    2swap definition-var 2swap ( env var val )
+
+    2rot ( var val env )
+    define-var
+
+    ok-symbol
 ;
+    
+: 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 )
 
-\ ---- REPL ----
+    2rot ( var val env )
+    set-var
+
+    ok-symbol
+;
 
-: escape 27 emit [char] [ emit ;
-: escape-end [char] m emit ;
+: if? ( obj -- obj bool )
+    if-symbol tagged-list? ;
 
-: set-term-colour
-    escape [char] 3 emit [char] 0 + emit escape-end
+: if-predicate ( ifobj -- pred )
+    cdr car ;
+
+: if-consequent ( ifobj -- conseq )
+    cdr cdr car ;
+
+: if-alternative ( ifobj -- alt|false )
+    cdr cdr cdr
+    2dup nil objeq? if
+        2drop false
+    else
+        car
+    then ;
+
+: false? ( boolobj -- boolean )
+    boolean-type istype? if
+        false boolean-type objeq?
+    else
+        2drop false
+    then
 ;
 
-: reset-term
-    escape [char] 0 escape-end
+: true? ( boolobj -- bool )
+    false? invert ;
+
+: 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 ;
+
+: list-of-vals ( args env -- vals )
+    2swap
+
+    2dup nooperands? if
+        2swap 2drop
+    else
+        2over 2over first-operand 2swap eval
+        -2rot rest-operands 2swap recurse
+        cons
+    then
 ;
 
-: colour
-    create ,
-does>
-    @ set-term-colour
+:noname ( obj env -- result )
+    2swap
+
+    self-evaluating? if
+        2swap 2drop
+        exit
+    then
+
+    quote? if
+        quote-body
+        2swap 2drop
+        exit
+    then
+
+    variable? if
+        2swap lookup-var
+        exit
+    then
+
+    definition? if
+        2swap eval-definition
+        exit
+    then
+
+    assignment? if
+        2swap eval-assignment
+        exit
+    then
+
+    if? if
+        2over 2over
+        if-predicate
+        2swap eval 
+
+        true? if
+            if-consequent
+        else
+            if-alternative
+        then
+
+        2swap ['] eval goto
+    then
+
+    application? if
+        2over 2over
+        operator 2swap eval
+
+        primitive-type istype? false = if
+            bold fg red ." Object not applicable. Aboring." reset-term cr
+            abort
+        then
+
+        -2rot
+        operands 2swap list-of-vals
+
+        2swap drop execute
+        exit
+    then
+
+    bold fg red ." Error evaluating expression - unrecognized type. Aborting." reset-term cr
+    abort
+; is eval
+
+\ }}}
+
+\ ---- Print ---- {{{
+
+defer print
+
+: printnum ( numobj -- ) drop 0 .R ;
+
+: printbool ( numobj -- )
+    drop if
+        ." #t"
+    else
+        ." #f"
+    then
 ;
 
-1 colour red
-2 colour green
-3 colour yellow
-4 colour blue
-5 colour magenta
-6 colour cyan
-7 colour white
+: printchar ( charobj -- )
+    drop
+    case
+        9 of ." #\tab" endof
+        bl of ." #\space" endof
+        '\n' of ." #\newline" endof
+        
+        dup ." #\" emit
+    endcase
+;
 
-create repl-buffer 161 allot
+: (printstring) ( stringobj -- )
+    nil-type istype? if 2drop exit then
 
-: repl
-    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
 
-    cr
+    cdr recurse
+;
+: printstring ( stringobj -- )
+    [char] " emit
+    (printstring)
+    [char] " emit ;
 
-    begin
-        green ." => " white
+: 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
+;
 
-        repl-buffer 1+ 160 expect cr
-        span @ repl-buffer !
+: printprim ( primobj -- )
+    2drop ." <primitive procedure>" ;
 
-        parseexp
-        \ eval
+:noname ( obj -- )
+    fixnum-type istype? if printnum 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-type istype? if printprim exit then
+
+    bold fg red ." Error printing expression - unrecognized type. Aborting" reset-term cr
+    abort
+; is print
+
+\ }}}
+
+\ ---- REPL ----
+
+: repl
+    cr ." Welcome to scheme.forth.jl!" cr
+       ." Use Ctrl-D to exit." cr
+
+    empty-parse-str
+
+    begin
+        cr bold fg green ." > " reset-term
+        read
+        global-env fetchobj eval
+        fg cyan ." ; " print reset-term
     again
 ;
 
 forth definitions
+
+\ vim:fdm=marker