Updated links in readme.

[scheme.forth.jl.git] / src / scheme.4th

diff --git a/src/scheme.4th b/src/scheme.4th
index 0f2fc0d..027a193 100644 (file)
--- a/src/scheme.4th
+++ b/src/scheme.4th
@@ -551,11 +551,16 @@ global-env obj!
   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
@@ -592,6 +597,8 @@ global-env obj!
   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
@@ -613,15 +620,32 @@ global-env obj!
     2drop
 ;
 
-: restore-continuation ( 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 -- )
 
-    2dup >R >R
+    >R >R \ Store obj on return stack
+
+    2dup >R >R \ Store copy of continuation on return stack
 
     restore-param-stack
 
-    R> R>
+    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
 ;
@@ -1769,7 +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
@@ -2073,6 +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
 ;
@@ -2156,9 +2196,6 @@ parse-idx-stack parse-idx-sp !
 
 \ }}}
 
-\ DEBUGGING
-xxxx
-
 \ ---- Loading files ---- {{{
 
 : load ( addr n -- finalResult )