-\ Scheme interpreter
-
vocabulary scheme
scheme definitions
include term-colours.4th
+include defer-is.4th
+
+\ ------ Types ------
0 constant number-type
1 constant boolean-type
2 constant character-type
-: istype? ( obj -- obj b )
+3 constant string-type
+4 constant nil-type
+5 constant pair-type
+6 constant symbol-type
+: istype? ( obj type -- obj bool )
over = ;
+\ ------ 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 !
+
+: 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 + @
+;
+
+: caar car car ;
+: cadr cdr car ;
+: cdar car cdr ;
+: cddr cdr cdr ;
+
+: nil 0 nil-type ;
+: nil? nil-type istype? ;
+
+: objvar create 0 , 0 , ;
+
+: 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+ @ ;
+
+objvar symbol-table
+nil symbol-table setobj
+
+: objeq? ( obj obj -- bool )
+ rot = -rot = and ;
+
+\ ---- Pre-defined symbols ----
+
+: (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
+
\ ---- Read ----
variable parse-idx
-variable dummy-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 -! ;
-: store-parse-idx
- parse-idx @ dummy-parse-idx ! ;
-
-: restore-parse-idx
- dummy-parse-idx @ parse-idx ! ;
-
-variable parse-str
-
: charavailable? ( -- bool )
- parse-str @ @ parse-idx @ >
-;
+ parse-str-span @ parse-idx @ > ;
: nextchar ( -- char )
- charavailable? if
- parse-str @ 1+ parse-idx @ + @
- else
- 0
- then
-;
+ charavailable? false = if getline then
+ parse-str parse-idx @ + @ ;
: whitespace? ( -- bool )
nextchar BL =
- nextchar '\n' = or
-;
+ nextchar '\n' = or ;
+
+: eof? ( -- bool )
+ nextchar 4 = ;
: delim? ( -- bool )
whitespace?
exit
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
;
: 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
+
+ swap dup rot + swap
+
+ do
+ i @ nextchar <> if
+ drop false
+ leave
+ then
+
+ inc-parse-idx
+ loop
+
+ delim? false = if drop false then
- restore-parse-idx
- true
+ 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
- restore-parse-idx true
+ charavailable? false = if pop-parse-idx false exit then
+
+ pop-parse-idx true
;
+: pair? ( -- bool )
+ nextchar [char] ( = ;
+
+: string? ( -- bool )
+ nextchar [char] " = ;
+
: readnum ( -- num-atom )
minus? dup if
inc-parse-idx
true
then
+ inc-parse-idx
+
boolean-type
;
-\ Parse a counted string into a scheme expression
-: read ( -- obj )
+: 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
+;
+
+: 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 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
+;
+
+defer read
+
+: 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
exit
then
- bold fg red ." Error parsing string starting at character '"
- nextchar emit
- ." '. Aborting." reset-term cr
- abort
-;
+ 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 recurse nil cons cons exit
+ then
+
+ eof? if
+ bold fg blue ." Moriturus te saluto." reset-term ." ok" cr
+ quit
+ then
+
+ \ Anything else is assumed to be a symbol
+ readsymbol charlist>symbol
+
+; is read
\ ---- Eval ----
: self-evaluating? ( obj -- obj bool )
- number-type istype? if true exit then
boolean-type istype? if true exit then
- false ;
+ number-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 tagged-list? ;
+
+: quote-body ( quote-obj -- quote-body-obj )
+ cadr ;
+
: eval
self-evaluating? if
exit
then
+ quote? if
+ quote-body
+ exit
+ then
+
bold fg red ." Error evaluating expression - unrecognized type. Aborting." reset-term cr
abort
;
\ ---- Print ----
-: printnum ( numobj -- ) drop . ;
+: printnum ( numobj -- ) drop 0 .R ;
: printbool ( numobj -- )
drop if
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-type istype? 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
+
+ 2dup car drop emit
+ cdr recurse
+;
+
+: printnil ( nilobj -- )
+ 2drop ." ()" ;
+
+defer print
+: printpair ( pairobj -- )
+ 2dup
+ car print
+ cdr
+ nil-type istype? if 2drop exit then
+ pair-type istype? if space recurse exit then
+ ." . " print
+;
+
+:noname ( obj -- )
+ number-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
+
+ 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
- getline
-
- eof? if
- cr bold fg blue ." Moriturus te saluto." reset-term
- exit
- then
-
- repl-buffer @ 0> if
- 0 parse-idx !
- read
- eval
- fg cyan print reset-term
- then
+ read
+ eval
+ fg cyan ." ; " print reset-term
again
;