X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=src%2Fscheme.4th;h=93d249650e2fdefa3cc98f31d9fa5a413963e12e;hb=f71c5f93aefa930fd0ac175416523bc6a101e3df;hp=9f744c0b9a6224bf12b99e928e62fbe71b5ac488;hpb=96ce36055ecce6550bfac3ffbc60a2de331c9e85;p=scheme.forth.jl.git

diff --git a/src/scheme.4th b/src/scheme.4th
index 9f744c0..93d2496 100644
--- a/src/scheme.4th
+++ b/src/scheme.4th
@@ -39,6 +39,7 @@ make-type pair-type
 make-type symbol-type
 make-type primitive-proc-type
 make-type compound-proc-type
+make-type continuation-type
 make-type port-type
 : istype? ( obj type -- obj bool )
     over = ;
@@ -75,12 +76,6 @@ create car-type-cells scheme-memsize allot
 create cdr-cells scheme-memsize allot
 create cdr-type-cells scheme-memsize allot
 
-variable gc-enabled
-false gc-enabled !
-
-: gc-enabled?
-    gc-enabled @ ;
-
 create nextfrees scheme-memsize allot
 :noname
     scheme-memsize 0 do
@@ -96,9 +91,7 @@ variable nextfree
     nextfree !
 
     nextfree @ scheme-memsize >= if
-        gc-enabled? if
-            collect-garbage
-        then
+      collect-garbage
     then
 
     nextfree @ scheme-memsize >= if
@@ -140,6 +133,10 @@ variable nextfree
     cdr-cells + !
 ;
 
+variable object-stack-base
+: init-object-stack-base
+  depth object-stack-base ! ;
+
 : nil 0 nil-type ;
 : nil? nil-type istype? ;
 
@@ -410,6 +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 ;
 
@@ -424,99 +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
@@ -529,6 +520,62 @@ global-env obj!
 
 \ }}}
 
+\ ---- Continuations ---- {{{
+
+: cons-return-stack ( -- listobj )
+  rsp@ 1- rsp0  = if
+    nil exit
+  then
+
+  nil rsp@ 1- rsp0 do
+    i 1+ @ fixnum-type 2swap cons
+  loop
+;
+
+: cons-param-stack ( -- listobj )
+  nil 
+
+  depth 2- object-stack-base @ = if
+    exit
+  then
+
+  depth 2- object-stack-base @ do
+        PSP0 i + 1 + @
+        PSP0 i + 2 + @
+
+        2swap cons
+    2 +loop
+;
+
+: make-continuation
+
+  cons-param-stack
+  cons-return-stack
+  cons drop continuation-type
+;
+
+: continuation->pstack-list
+  drop pair-type car ;
+
+: continuation->rstack-list
+  drop pair-type cdr ;
+
+: restore-param-stack ( continuation -- obj_stack continuation )
+
+  2dup >R >R
+  continuation->pstack-list
+
+  ( Idea: allocate stack space first using psp!,
+    then copy objects from list. )
+;
+
+: restore-continuation
+  \ TODO: replace current parameter and return stacks with
+  \ contents of continuation object.
+;
+
+\ }}}
+
 \ ---- Primitives ---- {{{
 
 : make-primitive ( cfa -- )
@@ -1669,6 +1716,10 @@ parse-idx-stack parse-idx-sp !
                ['] evaluate-eproc goto
         endof
 
+        continuation-type of
+          \ TODO: Apply continuation
+        endof
+
         except-message: ." object '" drop print ." ' not applicable." recoverable-exception throw
     endcase
 ;
@@ -1917,6 +1968,9 @@ parse-idx-stack parse-idx-sp !
 : printcomp ( primobj -- )
     2drop ." <compound procedure>" ;
 
+: printcont ( primobj --)
+    2drop ." <continuation>" ;
+
 : printnone ( noneobj -- )
     2drop ." Unspecified return value" ;
 
@@ -1935,6 +1989,7 @@ parse-idx-stack parse-idx-sp !
     pair-type istype? if ." (" printpair ." )" exit then
     primitive-proc-type istype? if printprim exit then
     compound-proc-type istype? if printcomp exit then
+    continuation-type istype? if printcont exit then
     none-type istype? if printnone exit then
     port-type istype? if printport exit then
 
@@ -1945,14 +2000,20 @@ parse-idx-stack parse-idx-sp !
 
 \ ---- Garbage Collection ---- {{{
 
-variable gc-stack-depth
+( 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.
 
-: enable-gc
-    depth gc-stack-depth !
-    true gc-enabled ! ;
+  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. )
 
-: disable-gc
-    false gc-enabled ! ;
 
 : pairlike? ( obj -- obj bool )
     pair-type istype? if true exit then
@@ -2029,7 +2090,7 @@ variable gc-stack-depth
     console-i/o-port obj@ gc-mark-obj
     global-env obj@ gc-mark-obj
 
-    depth gc-stack-depth @ do
+    depth object-stack-base @ do
         PSP0 i + 1 + @
         PSP0 i + 2 + @
 
@@ -2078,11 +2139,8 @@ variable gc-stack-depth
 
     include scheme-primitives.4th
 
-    enable-gc
-
+    init-object-stack-base
     s" scheme-library.scm" load 2drop
-
-    disable-gc
     
 \ }}}
 
@@ -2110,7 +2168,7 @@ variable gc-stack-depth
 : repl
     empty-parse-str
 
-    enable-gc
+    init-object-stack-base
 
     \ Display welcome message
     welcome-symbol nil cons global-env obj@ eval 2drop
@@ -2124,8 +2182,6 @@ variable gc-stack-depth
             throw false
         endcase
     until
-
-    disable-gc
 ;
 
 forth definitions