Implemented the empty list.

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

diff --git a/scheme.4th b/scheme.4th
index a4e2d07..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 = ;
 
@@ -165,15 +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
@@ -209,15 +217,23 @@ parse-idx-stack parse-idx-sp !
     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
+    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 )
 
@@ -238,6 +254,11 @@ parse-idx-stack parse-idx-sp !
         exit
     then
 
+    empty-list? if
+        readnil
+        exit
+    then
+
     eof? if
         bold fg blue ." Moriturus te saluto." reset-term ."  ok" cr
         quit
@@ -255,6 +276,7 @@ parse-idx-stack parse-idx-sp !
     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
@@ -285,17 +307,19 @@ parse-idx-stack parse-idx-sp !
         bl of ." #\space" endof
         '\n' of ." #\newline" endof
         
-        ." #\" emit
+        dup ." #\" emit
     endcase
-
-    trace
 ;
 
+: 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 ----