Implemented the empty list.

[scheme.forth.jl.git] / scheme.4th

diff --git a/scheme.4th b/scheme.4th
index bf57ac7..9a49053 100644 (file)
--- a/scheme.4th
+++ b/scheme.4th
@@ -1,5 +1,3 @@
-\ Scheme interpreter
-
 vocabulary scheme
 scheme definitions
 
@@ -8,6 +6,7 @@ include term-colours.4th
 0 constant number-type
 1 constant boolean-type
 2 constant character-type
+3 constant nil-type
 : istype? ( obj -- obj b )
     over = ;
 
@@ -18,7 +17,6 @@ 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 !
@@ -105,7 +103,7 @@ parse-idx-stack parse-idx-sp !
         inc-parse-idx
     repeat
 
-    delim? charavailable? false = or if
+    delim? if
         pop-parse-idx
         true
     else
@@ -124,16 +122,24 @@ parse-idx-stack parse-idx-sp !
     nextchar [char] f <>
     and if pop-parse-idx false exit then
 
-    pop-parse-idx
-    true
+    inc-parse-idx
+    delim? if
+        pop-parse-idx
+        true
+    else
+        pop-parse-idx
+        false
+    then
 ;
 
 : str-equiv? ( str -- bool )
+
     push-parse-idx
 
-    true
+    true -rot
 
     swap dup rot + swap
+
     do
         i @ nextchar <> if
             drop false
@@ -143,7 +149,7 @@ parse-idx-stack parse-idx-sp !
         inc-parse-idx
     loop
 
-    delim? <> if drop false then
+    delim? false = if drop false then
 
     pop-parse-idx
 ;
@@ -158,15 +164,24 @@ parse-idx-stack parse-idx-sp !
 
     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
+    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
 ;
 
+: empty-list? ( -- bool )
+    nextchar [char] ( <> if false exit then
+    push-parse-idx
+    inc-parse-idx
+    eatspaces
+    nextchar [char] ) <> if pop-parse-idx false exit then
+    pop-parse-idx true ;
+
+
 : readnum ( -- num-atom )
     minus? dup if
         inc-parse-idx
@@ -198,6 +213,27 @@ parse-idx-stack parse-idx-sp !
     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
+;
+
+: readnil ( -- nil-atom )
+    inc-parse-idx
+    eatspaces
+    inc-parse-idx
+
+    nil-type
+;
+
 \ Parse a scheme expression
 : read ( -- obj )
 
@@ -213,6 +249,16 @@ parse-idx-stack parse-idx-sp !
         exit
     then
 
+    character? if
+        readchar
+        exit
+    then
+
+    empty-list? if
+        readnil
+        exit
+    then
+
     eof? if
         bold fg blue ." Moriturus te saluto." reset-term ."  ok" cr
         quit
@@ -229,6 +275,8 @@ parse-idx-stack parse-idx-sp !
 : 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
@@ -252,10 +300,26 @@ parse-idx-stack parse-idx-sp !
     then
 ;
 
+: printchar ( charobj -- )
+    drop
+    case
+        9 of ." #\tab" endof
+        bl of ." #\space" endof
+        '\n' of ." #\newline" endof
+        
+        dup ." #\" emit
+    endcase
+;
+
+: 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 ----