--- gforth/except.fs	2002/09/24 17:57:28	1.4
+++ gforth/except.fs	2003/11/23 22:52:29	1.9
@@ -1,6 +1,6 @@
 \ catch, throw, etc.
 
-\ Copyright (C) 1999,2000 Free Software Foundation, Inc.
+\ Copyright (C) 1999,2000,2003 Free Software Foundation, Inc.
 
 \ This file is part of Gforth.
 
@@ -33,10 +33,52 @@ Defer store-backtrace
 ' noop IS store-backtrace
 \ [THEN]
 
-: (try) ( -- )
-    \ inline argument: address of the handler
+\ Ok, here's the story about how we get to the native code for the
+\ recovery code in case of a THROW, and why there is all this funny
+\ stuff being compiled by TRY and RECOVER:
+
+\ Upon a THROW, we cannot just return through the ordinary return
+\ address, but have to use a different one, for code after the
+\ RECOVER.  How do we do that, in a way portable between the various
+\ threaded and native code engines?  In particular, how does the
+\ native code engine learn about the address of the native recovery
+\ code?
+
+\ On the Forth level, we can compile only references to threaded code.
+\ The only thing that translates a threaded code address to a native
+\ code address is docol, which is only called with EXECUTE and
+\ friends.  So we start the recovery code with a docol, and invoke it
+\ with PERFORM; the recovery code then rdrops the superfluously
+\ generated return address and continues with the proper recovery
+\ code.
+
+\ At compile time, since we cannot compile a forward reference (to the
+\ recovery code) as a literal (backpatching does not work for
+\ native-code literals), we produce a data cell (wrapped in AHEAD
+\ ... THEN) that we can backpatch, and compile the address of that as
+\ literal.
+
+\ Overall, this leads to the following resulting code:
+
+\   ahead
+\ +><recovery address>-+
+\ | then               |
+\ +-lit                |
+\   (try)              |
+\   ...                |
+\   (recover)          |
+\   ahead              |
+\   docol: <-----------+
+\   rdrop
+\   ...
+\   then
+\   ...
+
+\ !! explain handler on-stack structure
+
+: (try) ( ahandler -- )
     r>
-    dup @ >r \ recovery address
+    swap >r \ recovery address
     rp@ 'catch >r
     sp@ >r
     fp@ >r
@@ -44,10 +86,12 @@ Defer store-backtrace
     handler @ >r
     rp@ handler !
     backtrace-empty on
-    cell+ >r ;
+    >r ;
 
 : try ( compilation  -- orig ; run-time  -- ) \ gforth
-    POSTPONE (try) >mark ; immediate compile-only
+    \ !! does not work correctly for gforth-native
+    POSTPONE ahead here >r >mark 1 cs-roll POSTPONE then
+    r> POSTPONE literal POSTPONE (try) ; immediate compile-only
 
 : (recover) ( -- )
     \ normal end of try block: restore handler, forget rest
@@ -63,7 +107,10 @@ Defer store-backtrace
 : recover ( compilation  orig1 -- orig2 ; run-time  -- ) \ gforth
     \ !! check using a special tag
     POSTPONE (recover)
-    POSTPONE else ; immediate compile-only
+    POSTPONE else
+    docol: here 0 , 0 , code-address! \ start a colon def 
+    postpone rdrop                    \ drop the return address
+; immediate compile-only
 
 : endtry ( compilation  orig -- ; run-time  -- ) \ gforth
     POSTPONE then ; immediate compile-only
@@ -81,16 +128,16 @@ is catch
 	[ here forthstart 9 cells + ! ]
 	store-backtrace
 	handler @ ?dup-0=-IF
-	    cr ." uncaught exception: " .error cr
+	    >stderr cr ." uncaught exception: " .error cr
 	    2 (bye)
-	    quit
+\	    quit
 	THEN
 	rp!
 	r> handler !
 	r> lp!
 	r> fp!
 	r> swap >r sp! drop r>
-	rdrop 'throw
+	rdrop 'throw r> perform
     THEN ;
 is throw