vocabulary scheme
scheme definitions
-\ Cons cell memory
-1000 constant memsize
-create car memsize allot
-create cdr memsize allot
-create types memsize allot
+include term-colours.4th
-0 constant symbol-type
-1 constant int-type
-2 constant list-type
-3 constant bool-type
+0 constant number-type
+1 constant boolean-type
+: istype? ( obj -- obj b )
+ over = ;
-variable nextfree
-0 nextfree !
-
-: stack
- create here 1+ , allot ;
+\ ---- Read ----
+variable parse-idx
+variable dummy-parse-idx
-: push ( st v -- )
- over @ !
- 1 swap +!
-;
+: store-parse-idx
+ parse-idx @ dummy-parse-idx ! ;
-: pop ( st -- v )
- dup @ ( s0 sp )
- 1- ( so sp' )
+: restore-parse-idx
+ dummy-parse-idx @ parse-idx ! ;
- 2dup = abort" Stack underflow."
-
- dup @ ( s0 sp' v )
- -rot swap ( v sp' s0 )
- !
-;
-
-100 stack parse-stack
-variable parse-idx
variable parse-str
-
-: inc-parse-idx parse-idx +! ;
-: dec-parse-idx parse-idx -! ;
-
-: ?charavailable ( -- bool )
+: charavailable? ( -- bool )
parse-str @ @ parse-idx @ >
;
: nextchar ( -- char )
- ?charavailable if
+ charavailable? if
parse-str @ 1+ parse-idx @ + @
else
0
then
;
-: ?whitespace ( -- bool )
+: whitespace? ( -- bool )
nextchar BL =
nextchar '\n' = or
;
-: ?delim ( -- bool )
- ?whitespace
+: delim? ( -- bool )
+ whitespace?
nextchar [char] ( = or
nextchar [char] ) = or
;
: eatspaces
begin
- ?whitespace
+ whitespace?
while
1 parse-idx +!
repeat
;
-: parsebool
-
- nextchar emit cr
- trace
+: digit? ( -- bool )
+ nextchar [char] 0 >=
+ nextchar [char] 9 <=
+ and ;
- false
- nextchar [char] # <> if exit then
+: minus? ( -- bool )
+ nextchar [char] - = ;
- 1 inc-parse-idx
-
- nextchar dup [char] t = swap [char] f = or
- not if
- 1 dec-parse-idx
+: number? ( -- bool )
+ digit? minus? or false = if
+ false
exit
then
- 1 inc-parse-idx
+ store-parse-idx
+ 1 parse-idx +!
- ?delim not if
- 2 dec-parse-idx
- exit
+ begin digit? while
+ 1 parse-idx +!
+ repeat
+
+ delim? charavailable? false = or if
+ restore-parse-idx
+ true
+ else
+ restore-parse-idx
+ false
then
;
-: parsetoken
+: boolean? ( -- bool )
+ nextchar [char] # <> if false exit then
- eatspaces
+ 1 parse-idx +!
- \ Parens
+ nextchar [char] t <>
+ nextchar [char] f <>
+ and if 1 parse-idx -! false exit then
- nextchar [char] ( = if
- \ todo
- exit
+ 1 parse-idx -!
+ true
+;
+
+: readnum ( -- num-atom )
+ minus? dup if
+ 1 parse-idx +!
then
- nextchar [char] ) = if
- \ todo
- exit
+ 0
+
+ begin digit? while
+ 10 * nextchar [char] 0 - +
+ 1 parse-idx +!
+ repeat
+
+ swap if negate then
+
+ number-type
+;
+
+: readbool ( -- bool-atom )
+ 1 parse-idx +!
+
+ nextchar [char] f = if
+ false
+ else
+ true
then
- parsebool if
- exit
- exit
+ boolean-type
;
\ Parse a counted string into a scheme expression
-: parseexp ( straddr n -- exp )
- 0 parse-idx !
+: read ( -- obj )
- begin
- parsetoken
- nextchar 0 =
- until
+ eatspaces
+
+ number? if
+ readnum
+ exit
+ then
+
+ boolean? if
+ readbool
+ exit
+ then
+
+ bold fg red ." Error parsing string starting at character '"
+ nextchar emit
+ ." '. Aborting." reset-term cr
+ abort
;
-\ ---- REPL ----
+\ ---- Eval ----
-: escape 27 emit [char] [ emit ;
-: escape-end [char] m emit ;
+: self-evaluating? ( obj -- obj bool )
+ number-type istype? if true exit then
+ boolean-type istype? if true exit then
+ false ;
-: set-term-colour
- escape [char] 3 emit [char] 0 + emit escape-end
+: eval
+ self-evaluating? if
+ exit
+ then
+
+ bold fg red ." Error evaluating expression - unrecognized type. Aborting." reset-term cr
+ abort
;
-: reset-term
- escape [char] 0 escape-end
+\ ---- Print ----
+
+: printnum ( numobj -- ) drop . ;
+: printbool ( numobj -- )
+ drop if
+ ." #t"
+ else
+ ." #f"
+ then
;
-: colour
- create ,
-does>
- @ set-term-colour
+: print ( obj -- )
+ ." ;"
+ number-type istype? if printnum exit then
+ boolean-type istype? if printbool exit then
;
-1 colour red
-2 colour green
-3 colour yellow
-4 colour blue
-5 colour magenta
-6 colour cyan
-7 colour white
+\ ---- REPL ----
create repl-buffer 161 allot
+repl-buffer parse-str !
-: repl
- repl-buffer parse-str !
-
- cr
+: getline
+ repl-buffer 1+ 160 expect cr span @ repl-buffer ! ;
- begin
- green ." => " white
+: eof?
+ repl-buffer @ 0= if false exit then
+ repl-buffer 1+ @ 4 <> if false exit then
+ true ;
- repl-buffer 1+ 160 expect cr
- span @ repl-buffer !
+: repl
+ cr ." Welcome to scheme.forth.jl!" cr
+ ." Use Ctrl-D to exit." cr
- parseexp
- \ eval
+ begin
+ cr bold fg green ." => " reset-term
+ getline
+
+ eof? if
+ 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
again
;