-\ Scheme interpreter
-
vocabulary scheme
scheme definitions
include term-colours.4th
+include defer-is.4th
0 constant number-type
1 constant boolean-type
2 constant character-type
+3 constant nil-type
+4 constant pair-type
: istype? ( obj -- obj b )
over = ;
+100 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 +!
+;
+
\ ---- 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
- restore-parse-idx
- true
+ 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
- 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] ( = ;
+
+
: 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
+;
+
+defer read
+
+: readpair ( -- obj )
+ inc-parse-idx
+ 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
+
+ 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
+
+ cons
+;
+
+\ Parse a scheme expression
+: (read) ( -- obj )
eatspaces
exit
then
+ character? if
+ readchar
+ exit
+ then
+
+ pair? if
+ readpair
+ exit
+ then
+
+ eof? if
+ 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
;
+' (read) is read
+
\ ---- Eval ----
: self-evaluating? ( obj -- obj bool )
number-type istype? if true exit then
boolean-type istype? if true exit then
+ character-type istype? if true exit then
+ nil-type istype? if true exit then
false ;
: eval
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 ----
+: printnil ( nilobj -- )
+ drop ." ()" ;
-create repl-buffer 161 allot
-repl-buffer parse-str !
+: print ( obj -- )
+ ." ; "
+ number-type istype? if printnum exit then
+ boolean-type istype? if printbool exit then
+ character-type istype? if printchar exit then
+ nil-type istype? if printnil exit then
-: getline
- repl-buffer 1+ 160 expect span @ repl-buffer ! ;
+ bold fg red ." Error printing expression - unrecognized type. Aborting" reset-term cr
+ abort
+;
-: eof?
- repl-buffer @ 0= if false exit then
- repl-buffer 1+ @ 4 <> if false exit then
- true ;
+\ ---- 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
;
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