Added defer/is to support mutual recursion.

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

diff --git a/scheme.4th b/scheme.4th
index 0bbfbf5..915edba 100644 (file)
--- a/scheme.4th
+++ b/scheme.4th
@@ -1,16 +1,37 @@
-\ 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 +!
+;
+
 \ ---- Read ----
 
 variable parse-idx
@@ -18,7 +39,6 @@ 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 !
@@ -135,11 +155,13 @@ 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
@@ -149,7 +171,7 @@ parse-idx-stack parse-idx-sp !
         inc-parse-idx
     loop
 
-    delim? <> if drop false then
+    delim? false = if drop false then
 
     pop-parse-idx
 ;
@@ -164,15 +186,19 @@ 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
 ;
 
+: pair? ( -- bool )
+    nextchar [char] ( = ;
+
+
 : readnum ( -- num-atom )
     minus? dup if
         inc-parse-idx
@@ -204,8 +230,63 @@ 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
+;
+
+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
+
+    cons
+;
+
 \ Parse a scheme expression
-: read ( -- obj )
+: (read) ( -- obj )
 
     eatspaces
 
@@ -219,6 +300,16 @@ parse-idx-stack parse-idx-sp !
         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
@@ -230,11 +321,15 @@ parse-idx-stack parse-idx-sp !
     abort
 ;
 
+' (read) 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
@@ -258,10 +353,26 @@ 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 ----