Added variable lookup.

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

diff --git a/scheme.4th b/scheme.4th
index 6d56d64..a05b898 100644 (file)
--- a/scheme.4th
+++ b/scheme.4th
@@ -16,7 +16,7 @@ include defer-is.4th
 : istype? ( obj type -- obj bool )
     over = ;
 
-\ ------ Memory ------
+\ ------ Cons cell memory ------
 
 1000 constant N
 create car-cells N allot
@@ -50,6 +50,18 @@ variable nextfree
     cdr-type-cells + @
 ;
 
+: set-car! ( obj pair-obj -- )
+    drop dup
+    rot swap  car-type-cells + !
+    car-cells + !
+;
+
+: set-cdr! ( obj pair-obj -- )
+    drop dup
+    rot swap  cdr-type-cells + !
+    cdr-cells + !
+;
+
 : caar car car ;
 : cadr cdr car ;
 : cdar car cdr ;
@@ -58,7 +70,7 @@ variable nextfree
 : nil 0 nil-type ;
 : nil? nil-type istype? ;
 
-: objvar create 0 , 0 , ;
+: objvar create nil swap , , ;
 
 : value@ ( objvar -- val ) @ ;
 : type@ ( objvar -- type ) 1+ @ ;
@@ -67,14 +79,13 @@ variable nextfree
 : setobj ( newobj objvar -- ) dup rot swap 1+ ! ! ; 
 : fetchobj ( objvar -- obj ) dup @ swap 1+ @ ; 
 
-objvar symbol-table
-nil symbol-table setobj
-
 : objeq? ( obj obj -- bool )
     rot = -rot = and ;
 
 \ ---- Pre-defined symbols ----
 
+objvar symbol-table
+
 : (create-symbol) ( addr n -- symbol-obj )
     dup 0= if
         2drop nil
@@ -104,7 +115,83 @@ nil symbol-table setobj
     does> dup @ swap 1+ @
 ;
 
-create-symbol quote quote
+create-symbol quote quote-symbol
+create-symbol define define-symbol
+create-symbol set! set!-symbol
+
+\ ---- Environments ----
+
+objvar global-env
+
+: enclosing-env ( env -- env )
+    cdr ;
+
+: first-frame ( env -- frame )
+    car ;
+
+: make-frame ( vars vals -- frame )
+    cons ;
+
+: frame-vars ( frame -- vars )
+    car ;
+
+: frame-vals ( frame -- vals )
+    cdr ;
+
+: add-binding ( var val frame -- )
+    2swap 2over frame-vals cons
+    2over set-car!
+    2swap 2over frame-vars cons
+    swap set-cdr!
+;
+
+: extend-env ( vars vals env -- env )
+    >R >R
+    make-frame
+    R> R>
+    cons
+;
+
+objvar vars
+objvar vals
+
+: lookup-var-frame ( var frame -- val? bool )
+    2dup frame-vars vars setobj
+    frame-vals vals setobj
+
+    begin
+        vars fetchobj nil objeq? false =
+    while
+        2dup vars fetchobj car objeq? if
+            2drop
+            vals fetchobj car true
+            exit
+        then
+
+        vars fetchobj cdr vars setobj
+        vals fetchobj cdr vals setobj
+    repeat
+
+    2drop false
+;
+
+: lookup-var ( var env -- val )
+    begin
+        2dup nil objeq? false =
+    while
+        2over 2over first-frame
+        lookup-var-frame if
+            -rot 2drop -rot 2drop
+            exit
+        then
+
+        enclosing-env
+    repeat
+
+    2drop 
+    bold fg red ." Unbound variable " print ." . Aborting." reset-term cr
+    abort
+;
 
 \ ---- Read ----
 
@@ -514,7 +601,7 @@ defer read
 
     nextchar [char] ' = if
         inc-parse-idx
-        quote recurse nil cons cons exit
+        quote-symbol recurse nil cons cons exit
     then
 
     eof? if
@@ -548,18 +635,22 @@ defer read
     then ;
 
 : quote? ( obj -- obj bool )
-    quote tagged-list?  ;
+    quote-symbol tagged-list?  ;
 
 : quote-body ( quote-obj -- quote-body-obj )
     cadr ;
     
-: eval
+: eval ( obj env -- result )
+    2swap
+
     self-evaluating? if
+        2swap 2drop
         exit
     then
 
     quote? if
         quote-body
+        2swap 2drop
         exit
     then
 
@@ -652,7 +743,7 @@ defer print
     begin
         cr bold fg green ." > " reset-term
         read
-        eval
+        global-env fetchobj eval
         fg cyan ." ; " print reset-term
     again
 ;