X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=scheme.4th;h=a05b898f42660dfb9863508e218f1ff8db4a7390;hb=9e0ea182c4546eeefad63a27d63f057df3fb42c5;hp=d3555a4e1bcdbb2e29ff737addd9ea8efba40eeb;hpb=d75e232b614baf3d82abf447daacc8fcefefbe85;p=scheme.forth.jl.git

diff --git a/scheme.4th b/scheme.4th
index d3555a4..a05b898 100644
--- a/scheme.4th
+++ b/scheme.4th
@@ -16,9 +16,9 @@ include defer-is.4th
 : istype? ( obj type -- obj bool )
     over = ;
 
-\ ------ Memory ------
+\ ------ Cons cell memory ------
 
-100 constant N
+1000 constant N
 create car-cells N allot
 create car-type-cells N allot
 create cdr-cells N allot
@@ -50,10 +50,27 @@ 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 ;
+: cddr cdr cdr ;
+
 : nil 0 nil-type ;
 : nil? nil-type istype? ;
 
-: objvar create 0 , 0 , ;
+: objvar create nil swap , , ;
 
 : value@ ( objvar -- val ) @ ;
 : type@ ( objvar -- type ) 1+ @ ;
@@ -62,8 +79,119 @@ variable nextfree
 : setobj ( newobj objvar -- ) dup rot swap 1+ ! ! ; 
 : fetchobj ( objvar -- obj ) dup @ swap 1+ @ ; 
 
+: objeq? ( obj obj -- bool )
+    rot = -rot = and ;
+
+\ ---- Pre-defined symbols ----
+
 objvar symbol-table
-nil symbol-table setobj
+
+: (create-symbol) ( addr n -- symbol-obj )
+    dup 0= if
+        2drop nil
+    else
+        2dup drop @ character-type 2swap
+        swap 1+ swap 1-
+        recurse
+
+        cons
+    then
+;
+
+: create-symbol ( -- )
+    bl word
+    count
+
+    (create-symbol)
+    drop symbol-type
+
+    2dup
+
+    symbol-table fetchobj
+    cons
+    symbol-table setobj
+
+    create swap , ,
+    does> dup @ swap 1+ @
+;
+
+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 ----
 
@@ -234,30 +362,6 @@ parse-idx-stack parse-idx-sp !
 : string? ( -- bool )
     nextchar [char] " = ;
 
-: initial? ( -- bool )
-    nextchar [char] A >= nextchar [char] Z <= and if true exit then
-    nextchar [char] a >= nextchar [char] z <= and if true exit then
-    nextchar [char] * = if true exit then
-    nextchar [char] / = if true exit then
-    nextchar [char] > = if true exit then
-    nextchar [char] < = if true exit then
-    nextchar [char] = = if true exit then
-    nextchar [char] ? = if true exit then
-    nextchar [char] ! = if true exit then
-    false
-;
-
-: symbol? ( -- bool )
-    initial? if true exit then
-    nextchar [char] + =
-    nextchar [char] - = or if
-        inc-parse-idx
-        delim? if dec-parse-idx true exit then
-        dec-parse-idx
-    then
-    false
-;
-
 : readnum ( -- num-atom )
     minus? dup if
         inc-parse-idx
@@ -353,14 +457,14 @@ parse-idx-stack parse-idx-sp !
     if
         nil? -rot 2drop
         if
-            true exit
+            2drop 2drop true exit
         else
-            false exit
+            2drop 2drop false exit
         then
     else
         nil? -rot 2drop
         if
-            false exit
+            2drop 2drop false exit
         then
     then
 
@@ -476,11 +580,6 @@ defer read
         exit
     then
 
-    symbol? if
-        readsymbol charlist>symbol
-        exit
-    then
-
     pair? if
         inc-parse-idx
 
@@ -500,26 +599,58 @@ defer read
         exit
     then
 
+    nextchar [char] ' = if
+        inc-parse-idx
+        quote-symbol recurse nil cons cons exit
+    then
+
     eof? if
         bold fg blue ." Moriturus te saluto." reset-term ."  ok" cr
         quit
     then
 
-    bold fg red ." Error parsing string starting at character '"
-    nextchar emit
-    ." '. Aborting." reset-term cr
-    abort
+    \ Anything else is assumed to be a symbol
+    readsymbol charlist>symbol
 
 ; is read
 
 \ ---- Eval ----
 
 : self-evaluating? ( obj -- obj bool )
-    true \ everything self-evaluating for now
+    boolean-type istype? if true exit then
+    number-type istype? if true exit then
+    character-type istype? if true exit then
+    string-type istype? if true exit then
+    nil-type istype? if true exit then
+
+    false
 ;
 
-: eval
+: tagged-list? ( obj tag-obj -- obj bool )
+    2over 
+    pair-type istype? false = if
+        2drop 2drop false
+    else
+        car objeq?
+    then ;
+
+: quote? ( obj -- obj bool )
+    quote-symbol tagged-list?  ;
+
+: quote-body ( quote-obj -- quote-body-obj )
+    cadr ;
+    
+: eval ( obj env -- result )
+    2swap
+
     self-evaluating? if
+        2swap 2drop
+        exit
+    then
+
+    quote? if
+        quote-body
+        2swap 2drop
         exit
     then
 
@@ -612,7 +743,7 @@ defer print
     begin
         cr bold fg green ." > " reset-term
         read
-        eval
+        global-env fetchobj eval
         fg cyan ." ; " print reset-term
     again
 ;