X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=src%2Fscheme.4th;h=027a1938634e528fd8dadc2bee859d39bfc71c9a;hb=c775ab2562b213ac96fe1803d4e7001a73e874a8;hp=2edd16da5fc43309c34387e9c4eb10afa0770ed3;hpb=c6aa8bc94536cbac6a7df5ad6872131665aeefeb;p=scheme.forth.jl.git

diff --git a/src/scheme.4th b/src/scheme.4th
index 2edd16d..027a193 100644
--- a/src/scheme.4th
+++ b/src/scheme.4th
@@ -548,14 +548,19 @@ global-env obj!
         2swap cons
     2 +loop
 
-  depth 2- fixnum-type 2swap cons
+  depth 2- 2/ fixnum-type 2swap cons
 ;
 
-: make-continuation
+: 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
@@ -564,35 +569,85 @@ global-env obj!
 : continuation->rstack-list
   drop pair-type cdr ;
 
-: restore-param-stack ( continuation -- obj_stack continuation )
+: 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
+  car drop 2*
   object-stack-base @ psp0 + + psp!
 
   R> R> 2dup cdr
   2swap
-  car drop 2- 0 swap do
+  stack-list-len 1- 0 swap do
 
       2dup car
-      PSP0 object-stack-base @ + i + 2 + !
-      PSP0 object-stack-base @ + i + 1 + !
+      PSP0 object-stack-base @ + i 2* + 2 + !
+      PSP0 object-stack-base @ + i 2* + 1 + !
       cdr
 
-  -2 +loop
+  -1 +loop
 
   2drop
+;
+
+( This word restores the return stack to that contained in the
+continuation object, and thus NEVER RETURNS. )
+: 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
-  \ TODO: replace current parameter and return stacks with
-  \ contents of continuation object.
+( This word restores the parameter and return stacks
+to those in the continuation object. The restoration of the 
+return stack means that execution continues at the point
+described in the continuation object, so this word NEVER RETURNS.
+
+Note that both obj and a false-obj are added to the parameter
+stack before the return stack is restored, so that make-continuation
+knows that this execution path is the result of a continuation
+restoration rather than the original call to make-continuation. )
+: 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
 ;
 
 \ }}}
@@ -1738,7 +1793,22 @@ parse-idx-stack parse-idx-sp !
         endof
 
         continuation-type of
-          \ TODO: Apply continuation
+            2swap
+            nil? if
+                except-message: ." Continuations expect exactly 1 argument."
+                recoverable-exception throw
+            then
+
+            2dup cdr
+
+            nil? invert 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
@@ -2042,6 +2112,7 @@ parse-idx-stack parse-idx-sp !
     symbol-type istype? if true exit then
     compound-proc-type istype? if true exit then
     port-type istype? if true exit then
+    continuation-type istype? if true exit then
 
     false
 ;
@@ -2125,8 +2196,6 @@ parse-idx-stack parse-idx-sp !
 
 \ }}}
 
-xxxx
-
 \ ---- Loading files ---- {{{
 
 : load ( addr n -- finalResult )