X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=scheme.4th;h=9a490539ea259917f160903018b578fd1c10f2bc;hb=62886ccdbb1bba3bf64abfb5b8f01cbf2c7f9f7e;hp=ea02cd513b424fd72efede52139568e87c758204;hpb=26a971100b29dee243a42096d52d69ca518905ea;p=scheme.forth.jl.git

diff --git a/scheme.4th b/scheme.4th
index ea02cd5..9a49053 100644
--- 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 = ;
 
@@ -134,11 +133,13 @@ parse-idx-stack parse-idx-sp !
 ;
 
 : str-equiv? ( str -- bool )
+
     push-parse-idx
 
-    true
+    true -rot
 
     swap dup rot + swap
+
     do
         i @ nextchar <> if
             drop false
@@ -148,7 +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
 ;
@@ -163,15 +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
@@ -207,15 +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 )
 
@@ -236,6 +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
@@ -252,6 +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
@@ -281,14 +306,20 @@ parse-idx-stack parse-idx-sp !
         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 ----