X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=scheme.4th;h=8c84378d879ca9e638f193f68629c29e81c0f631;hb=385421e5768281c250e22ac5d7ab8da026dea86c;hp=48ab5648416d721879a8d42faa654506f98cc184;hpb=123ce52c0fe63b568a3c9c11dc1b85d4dfd17c8e;p=scheme.forth.jl.git

diff --git a/scheme.4th b/scheme.4th
index 48ab564..8c84378 100644
--- a/scheme.4th
+++ b/scheme.4th
@@ -1,177 +1,396 @@
-\ Scheme interpreter
-
 vocabulary scheme
 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 symbol-type
-1 constant int-type
-2 constant list-type
-3 constant bool-type
+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 !
 
-: make-bool 
-    nextfree @
+: cons ( car-obj cdr-obj -- pair-obj )
+    cdr-type-cells nextfree @ + !
+    cdr-cells nextfree @ + !
+    car-type-cells nextfree @ + !
+    car-cells nextfree @ + !
 
-    car nextfree @ + !
-    cdr nextfree @ + 0 !
-    types nextfree @ + bool-type !
+    nextfree @ pair-type
 
     1 nextfree +!
 ;
 
-: stack
-    create here 1+ , allot ;
+\ ---- Read ----
 
+variable parse-idx
+variable stored-parse-idx
+create parse-str 161 allot
+variable parse-str-span
 
-: push ( st v -- )
-    over @ !
-    1 swap +!
+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 ( 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 ;
+
+: eof? ( -- bool )
+    nextchar 4 = ;
 
-: ?delim ( -- bool )
-    ?whitespace
+: delim? ( -- bool )
+    whitespace?
     nextchar [char] ( = or
     nextchar [char] ) = or
 ;
 
 : eatspaces
     begin
-        ?whitespace
+        whitespace?
     while
-            1 parse-idx +!
+        inc-parse-idx
+    repeat
+;
+
+: digit? ( -- bool )
+    nextchar [char] 0 >=
+    nextchar [char] 9 <=
+    and ;
+
+: minus? ( -- bool )
+    nextchar [char] - = ;
+
+: number? ( -- bool )
+    digit? minus? or false = if
+        false
+        exit
+    then
+
+    push-parse-idx
+    inc-parse-idx
+
+    begin digit? while
+        inc-parse-idx
     repeat
+
+    delim? if
+        pop-parse-idx
+        true
+    else
+        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
 ;
 
-: parsebool
+: 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
 
-    1 inc-parse-idx
+    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
+;
+
+: pair? ( -- bool )
+    nextchar [char] ( = ;
+
 
-    nextchar dup [char] t = swap [char] f = or
-    not if
-        1 dec-parse-idx
-        false exit
+: readnum ( -- num-atom )
+    minus? dup if
+        inc-parse-idx
     then
 
-    1 inc-parse-idx
+    0
 
-    ?delim not if
-        2 dec-parse-idx
-        false exit
+    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
-        1 dec-parse-idx
-        nextchar [char] t = make-bool
-        1 inc-parse-idx
-        true exit
+        true
     then
+
+    inc-parse-idx
+
+    boolean-type
 ;
 
-\ Set cdr at i to j, leaving j on the stack
-: append ( i j -- j )
-    dup rot
-    dup 0> if
-        cdr + !
+: 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
-        2drop
+        recurse
     then
+
+    cons
 ;
 
-: parsetoken
+\ 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
-        append
+    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
 ;
 
-\ Parse a counted string into a scheme expression
-: parseexp ( straddr n -- exp )
-    0 parse-idx !
+' (read) is read
 
-    begin
-        parsetoken
-    nextchar 0 =
-    until
+\ ---- 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
+    self-evaluating? if
+        exit
+    then
+
+    bold fg red ." Error evaluating expression - unrecognized type. Aborting." reset-term cr
+    abort
 ;
 
-\ ---- REPL ----
+\ ---- Print ----
 
-create repl-buffer 161 allot
+: printnum ( numobj -- ) drop . ;
 
-: repl
-    repl-buffer parse-str !
+: printbool ( numobj -- )
+    drop if
+        ." #t"
+    else
+        ." #f"
+    then
+;
 
-    cr
+: printchar ( charobj -- )
+    drop
+    case
+        9 of ." #\tab" endof
+        bl of ." #\space" endof
+        '\n' of ." #\newline" endof
+        
+        dup ." #\" emit
+    endcase
+;
 
-    begin
-        bold fg green ." => " reset-term
+: printnil ( nilobj -- )
+    drop ." ()" ;
+
+: 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
 
-        repl-buffer 1+ 160 expect cr
-        span @ repl-buffer !
+    bold fg red ." Error printing expression - unrecognized type. Aborting" reset-term cr
+    abort
+;
 
-        parseexp
-        \ eval
+\ ---- 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
+        read
+        eval
+        fg cyan print reset-term
     again
 ;