X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=scheme.4th;h=4dee70f16a352f0bf8f6ab483facb697a7db141d;hb=b2a917e726a54a7cc3b21b8559cd166d3c2100f7;hp=a05b898f42660dfb9863508e218f1ff8db4a7390;hpb=9e0ea182c4546eeefad63a27d63f057df3fb42c5;p=scheme.forth.jl.git

diff --git a/scheme.4th b/scheme.4th
index a05b898..4dee70f 100644
--- a/scheme.4th
+++ b/scheme.4th
@@ -16,7 +16,7 @@ include defer-is.4th
 : istype? ( obj type -- obj bool )
     over = ;
 
-\ ------ Cons cell memory ------
+\ ------ Cons cell memory ------ {{{
 
 1000 constant N
 create car-cells N allot
@@ -82,7 +82,9 @@ variable nextfree
 : objeq? ( obj obj -- bool )
     rot = -rot = and ;
 
-\ ---- Pre-defined symbols ----
+\ }}}
+
+\ ---- Pre-defined symbols ---- {{{
 
 objvar symbol-table
 
@@ -115,13 +117,14 @@ objvar symbol-table
     does> dup @ swap 1+ @
 ;
 
-create-symbol quote quote-symbol
-create-symbol define define-symbol
-create-symbol set! set!-symbol
+create-symbol quote     quote-symbol
+create-symbol define    define-symbol
+create-symbol set!      set!-symbol
+create-symbol ok        ok-symbol
 
-\ ---- Environments ----
+\ }}}
 
-objvar global-env
+\ ---- Environments ---- {{{
 
 : enclosing-env ( env -- env )
     cdr ;
@@ -155,7 +158,7 @@ objvar global-env
 objvar vars
 objvar vals
 
-: lookup-var-frame ( var frame -- val? bool )
+: get-vars-vals-frame ( var frame -- bool )
     2dup frame-vars vars setobj
     frame-vals vals setobj
 
@@ -163,8 +166,7 @@ objvar vals
         vars fetchobj nil objeq? false =
     while
         2dup vars fetchobj car objeq? if
-            2drop
-            vals fetchobj car true
+            2drop true
             exit
         then
 
@@ -175,25 +177,72 @@ objvar vals
     2drop false
 ;
 
-: lookup-var ( var env -- val )
+: get-vars-vals ( var env -- vars? vals? bool )
+
     begin
         2dup nil objeq? false =
     while
         2over 2over first-frame
-        lookup-var-frame if
-            -rot 2drop -rot 2drop
+        get-vars-vals-frame if
+            2drop 2drop
+            vars fetchobj vals fetchobj true
             exit
         then
 
         enclosing-env
     repeat
 
-    2drop 
-    bold fg red ." Unbound variable " print ." . Aborting." reset-term cr
-    abort
+    2drop 2drop
+    false
+;
+
+hide vars
+hide vals
+
+: lookup-var ( var env -- val )
+    get-vars-vals if
+        2swap 2drop car
+    else
+        bold fg red ." Tried to read unbound variable." reset-term abort
+    then
+;
+
+: set-var ( var val env -- )
+    >R >R 2swap R> R> ( val var env )
+    get-vars-vals if
+        2swap 2drop ( val vals )
+        set-car!
+    else
+        bold fg red ." Tried to set unbound variable." reset-term abort
+    then
+;
+
+objvar env
+
+: define-var ( var val env -- )
+    env setobj 
+
+    2over env fetchobj ( var val var env )
+    get-vars-vals if
+        2swap 2drop ( var val vals )
+        set-car!
+        2drop
+    else
+        env fetchobj
+        first-frame ( var val frame )
+        add-binding
+    then
 ;
 
-\ ---- Read ----
+hide env
+
+objvar global-env
+nil nil nil extend-env
+global-env setobj
+
+\ }}}
+
+\ ---- Read ---- {{{
 
 variable parse-idx
 variable stored-parse-idx
@@ -568,6 +617,7 @@ defer read
 
     string? if
         inc-parse-idx
+
         readstring
         drop string-type
 
@@ -577,6 +627,7 @@ defer read
         then
 
         inc-parse-idx
+
         exit
     then
 
@@ -609,12 +660,14 @@ defer read
         quit
     then
 
-    \ Anything else is assumed to be a symbol
+    \ Anything else is parsed as a symbol
     readsymbol charlist>symbol
 
 ; is read
 
-\ ---- Eval ----
+\ }}}
+
+\ ---- Eval ---- {{{
 
 : self-evaluating? ( obj -- obj bool )
     boolean-type istype? if true exit then
@@ -639,8 +692,59 @@ defer read
 
 : quote-body ( quote-obj -- quote-body-obj )
     cadr ;
+
+: variable? ( obj -- obj bool )
+    symbol-type istype? ;
+
+: definition? ( obj -- obj bool )
+    define-symbol tagged-list? ;
+
+: definition-var ( obj -- var )
+    cdr car ;
+
+: definition-val ( obj -- val )
+    cdr cdr car ;
+
+: assignment? ( obj -- obj bool )
+    set!-symbol tagged-list? ;
+
+: assignment-var ( obj -- var )
+    cdr car ;
+    
+: assignment-val ( obj -- val )
+    cdr cdr car ;
+
+defer eval
+
+: eval-definition ( obj env -- res )
+    2swap 
+    2over 2over ( env obj env obj )
+    definition-val 2swap ( env obj valexp env )
+    eval  ( env obj val )
     
-: eval ( obj env -- result )
+    2swap definition-var 2swap ( env var val )
+
+    >R >R 2swap R> R> 2swap ( var val env )
+    define-var
+
+    ok-symbol
+;
+    
+: eval-assignment ( obj env -- res )
+    2swap 
+    2over 2over ( env obj env obj )
+    assignment-val 2swap ( env obj valexp env )
+    eval  ( env obj val )
+    
+    2swap assignment-var 2swap ( env var val )
+
+    >R >R 2swap R> R> 2swap ( var val env )
+    set-var
+
+    ok-symbol
+;
+
+:noname ( obj env -- result )
     2swap
 
     self-evaluating? if
@@ -654,11 +758,28 @@ defer read
         exit
     then
 
+    variable? if
+        2swap lookup-var
+        exit
+    then
+
+    definition? if
+        2swap eval-definition
+        exit
+    then
+
+    assignment? if
+        2swap eval-assignment
+        exit
+    then
+
     bold fg red ." Error evaluating expression - unrecognized type. Aborting." reset-term cr
     abort
-;
+; is eval
+
+\ }}}
 
-\ ---- Print ----
+\ ---- Print ---- {{{
 
 : printnum ( numobj -- ) drop 0 .R ;
 
@@ -732,6 +853,8 @@ defer print
     abort
 ; is print
 
+\ }}}
+
 \ ---- REPL ----
 
 : repl