-\ Scheme interpreter
-
vocabulary scheme
scheme definitions
include term-colours.4th
0 constant number-type
+1 constant boolean-type
+2 constant character-type
: istype? ( obj -- obj b )
over = ;
\ ---- 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 -!
-: store-parse-idx
- parse-idx @ dummy-parse-idx ! ;
+ 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 ! ;
-: restore-parse-idx
- dummy-parse-idx @ parse-idx ! ;
+: inc-parse-idx
+ 1 parse-idx +! ;
-variable parse-str
+: dec-parse-idx
+ 1 parse-idx -! ;
: 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?
begin
whitespace?
while
- 1 parse-idx +!
+ inc-parse-idx
repeat
;
exit
then
- store-parse-idx
- 1 parse-idx +!
+ push-parse-idx
+ inc-parse-idx
begin digit? while
- 1 parse-idx +!
+ 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
+
+ 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
+;
+
: readnum ( -- num-atom )
minus? dup if
- 1 parse-idx +!
+ inc-parse-idx
then
0
begin digit? while
10 * nextchar [char] 0 - +
- 1 parse-idx +!
+ inc-parse-idx
repeat
swap if negate then
number-type
;
-\ Parse a counted string into a scheme expression
+: 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
+;
+
+\ Parse a scheme expression
: read ( -- obj )
eatspaces
+
number? if
readnum
exit
then
- ." Error parsing string at character" parse-idx ? ." . Aborting." cr
+ boolean? if
+ readbool
+ 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
abort
;
\ ---- Eval ----
: self-evaluating? ( obj -- obj bool )
- number-type istype? ;
+ number-type istype? if true exit then
+ boolean-type istype? if true exit then
+ character-type istype? if true exit then
+ false ;
: eval
self-evaluating? if
exit
then
- ." Error evaluating expression - unrecognized type. Aborting." cr
+ bold fg red ." Error evaluating expression - unrecognized type. Aborting." reset-term cr
abort
;
\ ---- Print ----
-: print ( obj -- )
- number-type istype? if
- drop .
+: printnum ( numobj -- ) drop . ;
+
+: printbool ( numobj -- )
+ drop if
+ ." #t"
+ else
+ ." #f"
then
;
-\ ---- REPL ----
-
-create repl-buffer 161 allot
-repl-buffer parse-str !
+: printchar ( charobj -- )
+ drop
+ case
+ 9 of ." #\tab" endof
+ bl of ." #\space" endof
+ '\n' of ." #\newline" endof
+
+ dup ." #\" emit
+ endcase
+;
-: getline
- repl-buffer 1+ 160 expect cr span @ repl-buffer ! ;
+: print ( obj -- )
+ ." ; "
+ number-type istype? if printnum exit then
+ boolean-type istype? if printbool exit then
+ character-type istype? if printchar exit then
+;
-: 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
- begin
- cr bold fg green ." => " reset-term
- getline
-
- eof? if
- fg blue ." Moriturus te saluto." reset-term
- exit
- then
+ empty-parse-str
- repl-buffer @ 0> if
- 0 parse-idx !
- read
- eval
- print
- then
+ begin
+ cr bold fg green ." > " reset-term
+ read
+ eval
+ fg cyan print reset-term
again
;
The Lambda Lab / projects / scheme.forth.jl.git / blobdiff