X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=scheme.4th;h=7fcbb30dd377f85e4e5ffe4bc1cf2e752aed0ace;hb=926748a17c5ba8eca3bc7379d3c52f6e94ef5c36;hp=8d9c97a8938a865d92ddf9326379fb027337ec3a;hpb=bc4c866824b12208394e0ca8d6468ed8cd5c49a8;p=scheme.forth.jl.git

diff --git a/scheme.4th b/scheme.4th
index 8d9c97a..7fcbb30 100644
--- a/scheme.4th
+++ b/scheme.4th
@@ -1,20 +1,87 @@
-\ Scheme interpreter
-
 vocabulary scheme
 scheme definitions
 
 include term-colours.4th
+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 !
+
+: cons ( car-obj cdr-obj -- pair-obj )
+    cdr-type-cells nextfree @ + !
+    cdr-cells nextfree @ + !
+    car-type-cells nextfree @ + !
+    car-cells nextfree @ + !
+
+    nextfree @ pair-type
+
+    1 nextfree +!
+;
+
+: car ( pair-obj -- car-obj )
+    drop
+    dup car-cells + @ swap
+    car-type-cells + @
+;
+
+: cdr ( pair-obj -- car-obj )
+    drop
+    dup cdr-cells + @ swap
+    cdr-type-cells + @
+;
+
+
 \ ---- 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 -!
+
+    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 ! ;
 
 : inc-parse-idx
     1 parse-idx +! ;
@@ -22,30 +89,19 @@ variable dummy-parse-idx
 : dec-parse-idx
     1 parse-idx -! ;
 
-: store-parse-idx
-    parse-idx @ dummy-parse-idx !  ;
-
-: restore-parse-idx
-    dummy-parse-idx @ parse-idx !  ;
-
-variable parse-str
-
 : 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?
@@ -75,18 +131,18 @@ variable parse-str
         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
 ;
@@ -94,32 +150,68 @@ variable parse-str
 : 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 )
 
-    restore-parse-idx
-    true
+    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
 
-    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
 ;
 
+: pair? ( -- bool )
+    nextchar [char] ( = ;
+
+
 : readnum ( -- num-atom )
     minus? dup if
         inc-parse-idx
@@ -146,11 +238,69 @@ variable parse-str
         true
     then
 
+    inc-parse-idx
+
     boolean-type
 ;
 
-\ Parse a counted string into a scheme expression
-: read ( -- obj )
+: 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
+        recurse
+    then
+
+    eatspaces
+
+    cons
+;
+
+\ Parse a scheme expression
+:noname ( -- obj )
 
     eatspaces
 
@@ -164,23 +314,42 @@ variable parse-str
         exit
     then
 
+    character? if
+        readchar
+        exit
+    then
+
+    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
-;
+
+; is read
 
 \ ---- 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
+    \ self-evaluating? if
+    \     exit
+    \ then
+    exit
 
     bold fg red ." Error evaluating expression - unrecognized type. Aborting." reset-term cr
     abort
@@ -188,7 +357,7 @@ variable parse-str
 
 \ ---- Print ----
 
-: printnum ( numobj -- ) drop . ;
+: printnum ( numobj -- ) drop 0 .R ;
 
 : printbool ( numobj -- )
     drop if
@@ -198,44 +367,55 @@ variable parse-str
     then
 ;
 
-: print ( obj -- )
-    ." ; "
-    number-type istype? if ." => " printnum exit then
-    boolean-type istype? if ." => " printbool exit then
+: printchar ( charobj -- )
+    drop
+    case
+        9 of ." #\tab" endof
+        bl of ." #\space" endof
+        '\n' of ." #\newline" endof
+        
+        dup ." #\" emit
+    endcase
 ;
 
-\ ---- REPL ----
+: printnil ( nilobj -- )
+    drop ." ()" ;
+
+defer print
+: printpair ( pairobj -- )
+    ." ("
+    2dup
+    car print
+    cdr
+    nil-type istype? if 2drop ." )" exit then
+    pair-type istype? if recurse ." )" exit then
+    ."  . " print ." )"
+;
 
-create repl-buffer 161 allot
-repl-buffer parse-str !
+:noname ( 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
+    pair-type istype? if printpair exit then
 
-: getline
-    repl-buffer 1+ 160 expect span @ repl-buffer ! ;
+    bold fg red ." Error printing expression - unrecognized type. Aborting" reset-term cr
+    abort
+; is print
 
-: 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
 
+    empty-parse-str
+
     begin
         cr bold fg green ." > " reset-term
-        getline
-
-        eof? if
-            cr 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
+        read
+        eval
+        fg cyan ." ; " print reset-term
     again
 ;