From: Tim Vaughan <tgvaughan@gmail.com>
Date: Tue, 31 Oct 2017 20:44:39 +0000 (+0100)
Subject: Merge branch 'master' into call-cc
X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?p=scheme.forth.jl.git;a=commitdiff_plain;h=f71c5f93aefa930fd0ac175416523bc6a101e3df;hp=1611b5484902b38774e0e61b84a14868dcc30152

Merge branch 'master' into call-cc
---

diff --git a/src/scheme.4th b/src/scheme.4th
index e94796c..93d2496 100644
--- a/src/scheme.4th
+++ b/src/scheme.4th
@@ -407,6 +407,9 @@ variable read-line-buffer-offset
 : make-frame ( vars vals -- frame )
     cons ;
 
+: add-frame-to-env ( frame env -- env )
+    cons ;
+
 : frame-vars ( frame -- vars )
     car ;
 
@@ -421,99 +424,90 @@ variable read-line-buffer-offset
 ;
 
 : extend-env ( vars vals env -- env )
-    >R >R
-    make-frame
-    R> R>
-    cons
+    -2rot make-frame
+    2swap add-frame-to-env
 ;
 
-objvar vars
-objvar vals
-
-: get-vars-vals-frame ( var frame -- bool )
-    2dup frame-vars vars obj!
-    frame-vals vals obj!
+: get-vals-frame ( var frame -- vals | nil )
+    2dup frame-vars 
+    2swap frame-vals ( var vars vals )
 
     begin
-        vars obj@ nil objeq? false =
+        nil? false =
     while
-        2dup vars obj@ car objeq? if
-            2drop true
+
+        -2rot ( vals var vars )
+        2over 2over car objeq? if
+            2drop 2drop
             exit
         then
 
-        vars obj@ cdr vars obj!
-        vals obj@ cdr vals obj!
+        cdr 2rot cdr
     repeat
 
-    2drop false
+    2drop 2drop 2drop
+    nil
 ;
 
-: get-vars-vals ( var env -- vars? vals? bool )
+: get-vals ( var env -- vals | nil )
 
     begin
         nil? false =
     while
         2over 2over first-frame
-        get-vars-vals-frame if
-            2drop 2drop
-            vars obj@ vals obj@ true
+        get-vals-frame nil? false = if
+            2swap 2drop 2swap 2drop
             exit
         then
 
+        2drop
+
         enclosing-env
     repeat
 
-    2drop 2drop
-    false
+    2swap 2drop
 ;
 
-hide vars
-hide vals
-
-objvar var
-
+objvar var \ Used only for error messages
 : lookup-var ( var env -- val )
     2over var obj!
-    get-vars-vals if
-        2swap 2drop car
-    else
-        except-message: ." tried to read unbound variable '" var obj@ print ." '." recoverable-exception  throw
+    
+    get-vals nil? if
+        except-message: ." tried to read unbound variable '" var obj@ print ." '."
+        recoverable-exception throw
     then
+
+    car
 ;
 
 : set-var ( var val env -- )
-    >R >R 2swap R> R> ( val var env )
-    2over var obj!
-    get-vars-vals if
-        2swap 2drop ( val vals )
-        set-car!
+    2rot 2dup var obj! ( val env var )
+    2swap ( val var env )
+    get-vals nil? if
+        except-message: ." tried to set unbound variable '" var obj@ print ." '."
+        recoverable-exception throw
     else
-        except-message: ." tried to set unbound variable '" var obj@ print ." '." recoverable-exception throw
+        ( val vals )
+        set-car!
     then
 ;
-
 hide var
 
-objvar env
-
 : define-var ( var val env -- )
-    env obj! 
+    first-frame ( var val frame )
+    2rot 2swap 2over 2over ( val var frame var frame )
 
-    2over env obj@ ( var val var env )
-    get-vars-vals if
-        2swap 2drop ( var val vals )
-        set-car!
+    get-vals-frame nil? if
         2drop
-    else
-        env obj@
-        first-frame ( var val frame )
+        -2rot 2swap 2rot
         add-binding
+    else
+        ( val var frame vals )
+        2swap 2drop 2swap 2drop
+        set-car!
     then
 ;
 
-hide env
-
 : make-procedure ( params body env -- proc )
     nil
     cons cons cons
@@ -2006,6 +2000,21 @@ parse-idx-stack parse-idx-sp !
 
 \ ---- Garbage Collection ---- {{{
 
+( Notes on garbage collection:
+  This is a mark-sweep garbage collector, invoked by cons.
+  The roots of the object tree used by the marking routine 
+  include all objects in the parameter stack, and several
+  other fixed roots such as global-env, symbol-table, macro-table,
+  and the console-i/o-port.
+
+  NO OTHER OBJECTS WILL BE MARKED!
+
+  This places implicit restrictions on when cons can be invoked.
+  Invoking cons when live objects are stored on the return stack
+  or in other variables than the above will result in possible
+  memory corruption if the cons triggers the GC. )
+
+
 : pairlike? ( obj -- obj bool )
     pair-type istype? if true exit then
     string-type istype? if true exit then