X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=scheme.4th;h=e1126ff0868bcc7a6bca3bdbefc1889d13a34ad1;hb=7c4b983db5c13783ed581b302becb7e8419123dc;hp=08a72b5380f53be0a757e46b54b2f3a6f2e41abe;hpb=7f58e8a0232663cd99ea18fd249d1e590ceb6fff;p=scheme.forth.jl.git

diff --git a/scheme.4th b/scheme.4th
index 08a72b5..e1126ff 100644
--- a/scheme.4th
+++ b/scheme.4th
@@ -1,23 +1,416 @@
-\ Scheme interpreter
-
 vocabulary scheme
 scheme definitions
 
 include term-colours.4th
+include defer-is.4th
+include throw-catch.4th
+
+defer read
+defer eval
+defer print
+
+\ ------ Types ------
 
-0 constant number-type
-1 constant boolean-type
-2 constant character-type
-: istype? ( obj -- obj b )
+variable nexttype
+0 nexttype !
+: make-type
+    create nexttype @ ,
+    nexttype @ 1+ nexttype !
+    does> @ ;
+
+make-type fixnum-type
+make-type real-type
+make-type boolean-type
+make-type character-type
+make-type string-type
+make-type nil-type
+make-type pair-type
+make-type symbol-type
+make-type primitive-proc-type
+make-type compound-proc-type
+: istype? ( obj type -- obj bool )
     over = ;
 
-\ ---- Read ----
+\ ------ Cons cell memory ------ {{{
+
+10000 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 !
+
+: cons ( car-obj cdr-obj -- pair-obj )
+    cdr-type-cells nextfree @ + !
+    cdr-cells nextfree @ + !
+    car-type-cells nextfree @ + !
+    car-cells nextfree @ + !
+
+    nextfree @ pair-type
+
+    1 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 + !
+;
+
+: caar car car ;
+: cadr cdr car ;
+: cdar car cdr ;
+: cddr cdr cdr ;
+
+: nil 0 nil-type ;
+: nil? nil-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>
+;
+
+\ }}}
+
+\ ---- 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
+        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!
+;
+
+
+: (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 obj@
+    cons
+    symbol-table obj!
+
+    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
+create-symbol lambda    lambda-symbol
+create-symbol λ         λ-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
+        2dup nil objeq? 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
+        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 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
+
+objvar global-env
+nil nil nil extend-env
+global-env obj!
+
+\ }}}
+
+\ ---- Primitives ---- {{{
+
+: make-primitive ( cfa -- )
+    bl word
+    count
+
+    (create-symbol)
+    drop symbol-type
+    
+    2dup
+
+    symbol-table obj@
+    cons
+    symbol-table obj!
+
+    rot primitive-proc-type ( var prim )
+    global-env obj@ define-var
+;
+
+: arg-count-error
+            bold fg red ." Incorrect argument count." reset-term cr
+            abort
+;
+
+: 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 ---- {{{
 
 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 +! ;
@@ -38,12 +431,6 @@ variable parse-str-span
 : dec-parse-idx
     1 parse-idx -! ;
 
-: store-parse-idx
-    parse-idx @ stored-parse-idx !  ;
-
-: restore-parse-idx
-    stored-parse-idx @ parse-idx !  ;
-
 : charavailable? ( -- bool )
     parse-str-span @ parse-idx @ > ;
 
@@ -64,12 +451,27 @@ variable parse-str-span
     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
+        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 )
@@ -80,24 +482,37 @@ variable parse-str-span
 : minus? ( -- bool )
     nextchar [char] - = ;
 
-: number? ( -- bool )
-    digit? minus? or false = if
-        false
-        exit
+: 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
 
-    store-parse-idx
+    push-parse-idx
     inc-parse-idx
 
     begin digit? while
         inc-parse-idx
     repeat
 
-    delim? charavailable? false = or if
-        restore-parse-idx
+    delim? if
+        pop-parse-idx
         true
     else
-        restore-parse-idx
+        pop-parse-idx
         false
     then
 ;
@@ -105,35 +520,76 @@ variable parse-str-span
 : boolean? ( -- bool )
     nextchar [char] # <> if false exit then
 
-    store-parse-idx
+    push-parse-idx
     inc-parse-idx
 
     nextchar [char] t <>
     nextchar [char] f <>
-    and if restore-parse-idx false exit then
+    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
 
-    restore-parse-idx
-    true
+    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
 
-    store-parse-idx
+    push-parse-idx
     inc-parse-idx
 
-    nextchar [char] \ <> if restore-parse-idx false exit then
+    nextchar [char] \ <> if pop-parse-idx false exit then
 
     inc-parse-idx
 
-    charavailable? false = if restore-parse-idx false exit then
+    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
 
-    restore-parse-idx true
+    pop-parse-idx true
 ;
 
+: pair? ( -- bool )
+    nextchar [char] ( = ;
+
+: string? ( -- bool )
+    nextchar [char] " = ;
+
 : readnum ( -- num-atom )
-    minus? dup if
+    plus? minus? or if
+        minus?
         inc-parse-idx
+    else
+        false
     then
 
     0
@@ -145,7 +601,7 @@ variable parse-str-span
 
     swap if negate then
 
-    number-type
+    fixnum-type
 ;
 
 : readbool ( -- bool-atom )
@@ -162,12 +618,109 @@ variable parse-str-span
     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
-: read ( -- obj )
+:noname ( -- obj )
 
     eatspaces
 
-    number? if
+    fixnum? if
         readnum
         exit
     then
@@ -177,36 +730,344 @@ variable parse-str-span
         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
+
     eof? if
+        inc-parse-idx
         bold fg blue ." Moriturus te saluto." reset-term ."  ok" cr
         quit
     then
 
-    bold fg red ." Error parsing string starting at character '"
-    nextchar emit
-    ." '. Aborting." reset-term cr
-    abort
-;
+    \ 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 ----
+\ ---- Eval ---- {{{
 
 : self-evaluating? ( obj -- obj bool )
-    number-type istype? if true exit then
     boolean-type istype? if true exit then
-    false ;
+    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
+;
+
+: 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 )
+    cadr ;
+
+: variable? ( obj -- obj bool )
+    symbol-type istype? ;
+
+: definition? ( obj -- obj bool )
+    define-symbol tagged-list? ;
+
+: make-lambda ( params body -- lambda-exp )
+    lambda-symbol -2rot cons cons ;
+
+: definition-var ( obj -- var )
+    cdr car
+    symbol-type istype? false = if car then
+;
+
+: definition-val ( obj -- val )
+    2dup cdr car symbol-type istype? if
+        2drop
+        cdr cdr car
+    else
+        cdr 2swap cdr cdr
+        make-lambda
+    then
+;
+
+: 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 )
+
+    2rot ( var val env )
+    set-var
+
+    ok-symbol
+;
+
+: 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|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
+;
+
+: 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 ;
+
+: make-procedure ( params body env -- proc )
+    nil
+    cons cons cons
+    drop compound-proc-type
+;
+
+: 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
+;
+
+: 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 ;
+
+: apply ( proc args )
+        2swap dup case
+            primitive-proc-type of
+                drop execute
+            endof
+
+            compound-proc-type of
+                2dup procedure-body ( args proc body )
+                -2rot 2dup procedure-params ( body args proc params )
+                -2rot procedure-env ( body params args procenv )
+
+                extend-env ( body env )
+
+                2swap ( env body )
+
+                begin
+                    2dup cdr 2dup nil objeq? false =
+                while
+                    -2rot car 2over ( nextbody env exp env )
+                    eval
+                    2drop \ discard result
+                    2swap ( env nextbody )
+                repeat
+
+                2drop ( env body )
+                car 2swap ( exp env )
+
+                R> drop ['] eval goto-deferred  \ Tail call optimization
+            endof
+
+            bold fg red ." Object not applicable. Aboring." reset-term cr
+            abort
+        endcase
+;
+
+:noname ( obj env -- result )
+    2swap
 
-: eval
     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-deferred
+    then
+
+    lambda? if
+        2dup lambda-parameters
+        2swap lambda-body
+        2rot make-procedure
+        exit
+    then
+
+    application? if
+        2over 2over
+        operator 2swap eval
+        -2rot
+        operands 2swap list-of-vals
+
+        apply
         exit
     then
 
     bold fg red ." Error evaluating expression - unrecognized type. Aborting." reset-term cr
     abort
-;
+; is eval
+
+\ }}}
 
-\ ---- Print ----
+\ ---- Print ---- {{{
 
-: printnum ( numobj -- ) drop . ;
+: printnum ( numobj -- ) drop 0 .R ;
 
 : printbool ( numobj -- )
     drop if
@@ -216,12 +1077,77 @@ variable parse-str-span
     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
+;
+
+: (printstring) ( stringobj -- )
+    nil-type istype? 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>" ;
+
+: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-proc-type istype? if printprim exit then
+    compound-proc-type istype? if printcomp exit then
+
+    bold fg red ." Error printing expression - unrecognized type. Aborting" reset-term cr
+    abort
+; is print
+
+\ }}}
+
 \ ---- REPL ----
 
 : repl
@@ -233,9 +1159,11 @@ variable parse-str-span
     begin
         cr bold fg green ." > " reset-term
         read
-        eval
-        fg cyan print reset-term
+        global-env obj@ eval
+        fg cyan ." ; " print reset-term
     again
 ;
 
 forth definitions
+
+\ vim:fdm=marker