X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=scheme.4th;h=a4e2d070ed72794a6348f502d1f75f12c813631c;hb=05e51ddd2d399b1a5c512aa355618a7d044e393f;hp=65c64a895b702796b7c36343d5e6a0182be2d023;hpb=ab2c14cdd02f93d17f8784e790415de0e6d7b996;p=scheme.forth.jl.git

diff --git a/scheme.4th b/scheme.4th
index 65c64a8..a4e2d07 100644
--- a/scheme.4th
+++ b/scheme.4th
@@ -5,151 +5,312 @@ scheme definitions
 
 include term-colours.4th
 
-\ Cons cell memory
-1000 constant memsize
-create car memsize allot
-create cdr memsize allot
-create types memsize allot
+0 constant number-type
+1 constant boolean-type
+2 constant character-type
+: istype? ( obj -- obj b )
+    over = ;
 
-0 constant symbol-type
-1 constant int-type
-2 constant list-type
-3 constant bool-type
+\ ---- Read ----
 
-variable nextfree
-0 nextfree !
-
-: stack
-    create here 1+ , allot ;
+variable 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 ( st v -- )
-    over @ !
-    1 swap +!
+: push-parse-idx
+    parse-idx @ parse-idx-sp @ !
+    1 parse-idx-sp +!
 ;
 
-: pop ( st -- v )
-    dup @       ( s0 sp )
-    1-          ( so sp' )
+: pop-parse-idx
+    parse-idx-sp @ parse-idx-stack <= abort" Parse index stack underflow."
 
-    2dup = abort" Stack underflow."
-    
-    dup @       ( s0 sp' v )
-    -rot swap   ( v sp' s0 )
-    !
-;
+    1 parse-idx-sp -!
 
-100 stack parse-stack 
-variable parse-idx
-variable parse-str
+    parse-idx-sp @ @ parse-idx ! ;
 
 
-: inc-parse-idx parse-idx +! ;
-: dec-parse-idx parse-idx -! ;
+: append-newline
+    '\n' parse-str parse-str-span @ + !
+    1 parse-str-span +! ;
 
-: ?charavailable ( -- bool )
-    parse-str @ @ parse-idx @ >
-;
+: 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 -! ;
+
+: charavailable? ( -- bool )
+    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 )
+: whitespace? ( -- bool )
     nextchar BL = 
-    nextchar '\n' = or
-;
+    nextchar '\n' = or ;
 
-: ?delim ( -- bool )
-    ?whitespace
+: eof? ( -- bool )
+    nextchar 4 = ;
+
+: delim? ( -- bool )
+    whitespace?
     nextchar [char] ( = or
     nextchar [char] ) = or
 ;
 
 : eatspaces
     begin
-        ?whitespace
+        whitespace?
     while
-            1 parse-idx +!
+        inc-parse-idx
     repeat
 ;
 
-: parsebool
+: digit? ( -- bool )
+    nextchar [char] 0 >=
+    nextchar [char] 9 <=
+    and ;
 
-    nextchar emit cr
-    trace
+: minus? ( -- bool )
+    nextchar [char] - = ;
 
-    false
-    nextchar [char] # <> if exit then
+: number? ( -- bool )
+    digit? minus? or false = if
+        false
+        exit
+    then
 
-    1 inc-parse-idx
+    push-parse-idx
+    inc-parse-idx
 
-    nextchar dup [char] t = swap [char] f = or
-    not if
-        1 dec-parse-idx
-        exit
+    begin digit? while
+        inc-parse-idx
+    repeat
+
+    delim? if
+        pop-parse-idx
+        true
+    else
+        pop-parse-idx
+        false
     then
+;
 
-    1 inc-parse-idx
+: boolean? ( -- bool )
+    nextchar [char] # <> if false exit then
 
-    ?delim not if
-        2 dec-parse-idx
-        exit
+    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
 ;
 
-: parsetoken
+: 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 true exit then
+    S" space" str-equiv? if true exit then
+    S" tab" str-equiv? if true exit then
+
+    charavailable? false = if pop-parse-idx false exit then
+
+    pop-parse-idx true
+;
+
+: readnum ( -- num-atom )
+    minus? dup if
+        inc-parse-idx
+    then
+
+    0
+
+    begin digit? while
+        10 * nextchar [char] 0 - +
+        inc-parse-idx
+    repeat
+
+    swap if negate then
+
+    number-type
+;
+
+: 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 '\n' character-type exit then
+    S" space" str-equiv? if bl character-type exit then
+    S" tab" str-equiv? if 9 character-type exit then
+
+    nextchar character-type
+
+    inc-parse-idx
+;
+
+\ Parse a scheme expression
+: read ( -- obj )
 
     eatspaces
 
-    \ Parens
+    number? if
+        readnum
+        exit
+    then
 
-    nextchar [char] ( = if
-        \ todo
+    boolean? if
+        readbool
         exit
     then
 
-    nextchar [char] ) = if
-        \ todo
+    character? if
+        readchar
         exit
     then
 
-    parsebool if
+    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? if true exit then
+    boolean-type istype? if true exit then
+    character-type istype? if true exit then
+    false ;
+
+: eval
+    self-evaluating? if
         exit
-    exit
+    then
+
+    bold fg red ." Error evaluating expression - unrecognized type. Aborting." reset-term cr
+    abort
 ;
 
-\ Parse a counted string into a scheme expression
-: parseexp ( straddr n -- exp )
-    0 parse-idx !
+\ ---- Print ----
 
-    begin
-        parsetoken
-    nextchar 0 =
-    until
+: printnum ( numobj -- ) drop . ;
+
+: printbool ( numobj -- )
+    drop if
+        ." #t"
+    else
+        ." #f"
+    then
 ;
 
-\ ---- REPL ----
+: printchar ( charobj -- )
+    drop
+    case
+        9 of ." #\tab" endof
+        bl of ." #\space" endof
+        '\n' of ." #\newline" endof
+        
+        ." #\" emit
+    endcase
 
-create repl-buffer 161 allot
+    trace
+;
 
-: repl
-    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
+;
 
-    cr
+\ ---- REPL ----
 
-    begin
-        bold fg green ." => " reset-term
+: repl
+    cr ." Welcome to scheme.forth.jl!" cr
+       ." Use Ctrl-D to exit." cr
 
-        repl-buffer 1+ 160 expect cr
-        span @ repl-buffer !
+    empty-parse-str
 
-        parseexp
-        \ eval
+    begin
+        cr bold fg green ." > " reset-term
+        read
+        eval
+        fg cyan print reset-term
     again
 ;