-\ Scheme interpreter
-
vocabulary scheme
scheme definitions
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
- 1 parse-str-span +!
- '\n' parse-str parse-str-span @ + ! ;
+ '\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
+ parse-str 160 expect cr
span @ parse-str-span !
append-newline
0 parse-idx ! ;
: 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 @ >
-;
+ parse-str-span @ parse-idx @ > ;
: nextchar ( -- char )
charavailable? false = if getline then
: 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
- restore-parse-idx
- true
+ 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
;
: readnum ( -- num-atom )
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
+;
+
\ Parse a scheme expression
: read ( -- obj )
exit
then
+ character? if
+ readchar
+ 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
: 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
false ;
: eval
then
;
+: printchar ( charobj -- )
+ drop
+ case
+ 9 of ." #\tab" endof
+ bl of ." #\space" endof
+ '\n' of ." #\newline" endof
+
+ dup ." #\" emit
+ endcase
+;
+
: print ( obj -- )
." ; "
- number-type istype? if ." => " printnum exit then
- boolean-type istype? if ." => " printbool exit then
+ number-type istype? if printnum exit then
+ boolean-type istype? if printbool exit then
+ character-type istype? if printchar exit then
;
\ ---- 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