X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=src%2Fscheme.4th;h=9d646677e32ac788581914cb3201462bb417f51f;hb=f1f104259426dc77ec46ae1ac3bda65fcc19a034;hp=2a509e68bca3285e05d95293c3dfb11757bba117;hpb=5bec487b30262d835382a1614027193dc1eb76fb;p=scheme.forth.jl.git

diff --git a/src/scheme.4th b/src/scheme.4th
index 2a509e6..9d64667 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? ;
 
@@ -523,6 +520,127 @@ 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
+
+  rsp@ 1- rsp0 - fixnum-type 2swap cons
+;
+
+: 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
+
+  depth 2- 2/ fixnum-type 2swap cons
+;
+
+: make-continuation ( -- continuation true-obj )
+    \ true-obj allows calling code to detect whether
+    \ it is being called immediately following make-continuation
+    \ or by a restore-continuation.
+
+  cons-param-stack
+  cons-return-stack
+  cons drop continuation-type
+
+  true boolean-type
+;
+
+: continuation->pstack-list
+  drop pair-type car ;
+
+: continuation->rstack-list
+  drop pair-type cdr ;
+
+: stack-list-len ( stack-list -- n )
+    car drop
+;
+
+: restore-param-stack ( continuation -- obj_stack )
+  continuation->pstack-list
+  2dup >R >R
+
+  ( Allocate stack space first using psp!,
+    then copy objects from list. )
+
+  car drop 2*
+  object-stack-base @ psp0 + + psp!
+
+  R> R> 2dup cdr
+  2swap
+  stack-list-len 1- 0 swap do
+
+      2dup car
+      PSP0 object-stack-base @ + i 2* + 2 + !
+      PSP0 object-stack-base @ + i 2* + 1 + !
+      cdr
+
+  -1 +loop
+
+  2drop
+;
+
+: restore-return-stack ( continuation -- )
+
+    continuation->rstack-list
+
+    2dup cdr 2swap stack-list-len ( list n )
+
+    dup RSP0 + RSP! \ expand return stack to accommodate entries
+
+    ( list n )
+
+    1-  \ initial offset n-1
+    0   \ final offset 0
+    swap
+    do
+        2dup cdr 2swap car drop
+        RSP0 i 1+ + !
+    -1 +loop
+
+    2drop
+;
+
+: restore-continuation-with-arg ( continuation obj -- )
+
+    >R >R \ Store obj on return stack
+
+    2dup >R >R \ Store copy of continuation on return stack
+
+    restore-param-stack
+
+    R> R> \ Pop continuation from return stack
+
+    R> R> \ Pop obj from return stack
+
+    2swap
+
+    false boolean-type \ Add flag signifying continuation restore
+
+    2swap
+
+    restore-return-stack
+;
+
+\ }}}
+
 \ ---- Primitives ---- {{{
 
 : make-primitive ( cfa -- )
@@ -1663,6 +1781,25 @@ parse-idx-stack parse-idx-sp !
                ['] evaluate-eproc goto
         endof
 
+        continuation-type of
+            2swap
+            nil? if
+                except-message: ." Continuations expect exactly 1 argument."
+                recoverable-exception throw
+            then
+
+            2dup cdr
+
+            nil? not if
+                except-message: ." Continuations expect exactly 1 argument."
+                recoverable-exception throw
+            then
+
+            2drop car
+                
+            restore-continuation-with-arg
+        endof
+
         except-message: ." object '" drop print ." ' not applicable." recoverable-exception throw
     endcase
 ;
@@ -1911,6 +2048,9 @@ parse-idx-stack parse-idx-sp !
 : printcomp ( primobj -- )
     2drop ." <compound procedure>" ;
 
+: printcont ( primobj --)
+    2drop ." <continuation>" ;
+
 : printnone ( noneobj -- )
     2drop ." Unspecified return value" ;
 
@@ -1929,6 +2069,7 @@ 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
 
@@ -1953,14 +2094,6 @@ parse-idx-stack parse-idx-sp !
   or in other variables than the above will result in possible
   memory corruption if the cons triggers the GC. )
 
-variable gc-stack-depth
-
-: enable-gc
-    depth gc-stack-depth !
-    true gc-enabled ! ;
-
-: disable-gc
-    false gc-enabled ! ;
 
 : pairlike? ( obj -- obj bool )
     pair-type istype? if true exit then
@@ -2037,7 +2170,7 @@ 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 + @
 
@@ -2086,11 +2219,8 @@ variable gc-stack-depth
 
     include scheme-primitives.4th
 
-    enable-gc
-
+    init-object-stack-base
     s" scheme-library.scm" load 2drop
-
-    disable-gc
     
 \ }}}
 
@@ -2118,7 +2248,7 @@ 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
@@ -2132,8 +2262,6 @@ variable gc-stack-depth
             throw false
         endcase
     until
-
-    disable-gc
 ;
 
 forth definitions