March 2014 update

Task/Exceptions/ALGOL-68/exceptions-1.alg

@@ -1,6 +1,9 @@
 # a user defined object #
-MODE OBJECTFOO = STRUCT ( PROC (REF OBJECTFOO)BOOL foo event mended, ... );
+MODE FOO = STRUCT ( ... )
+  FOOOBJECTNEW = STRUCT (FOOMEND foo exception x mended, FOO instance),
+  FOOOBJECT = REF FOOOBJECTNEW,
+  FOOMEND = PROC (FOOOBJECT)BOOL;
 
-PROC on foo event = (REF OBJECTFOO foo, PROC (REF OBJECTFOO)BOOL foo event)VOID: (
-  foo event mended OF foo := foo event
+PROC on foo exception x = (FOOOBJECT foo, PROC (FOOOBJECT)BOOL foo exception x mend)VOID: (
+  foo exception x mended OF foo := foo exception x mend
 );

Task/Exceptions/ALGOL-68/exceptions-2.alg

@@ -1,8 +1,4 @@
-OBJECTFOO foo proxy := foo base; # event routines are specific to an foo #
-
-on foo event(foo proxy, raise foo event);
-
-WHILE TRUE DO
-  # now raise example foo event #
-  IF NOT (foo event mended OF foo proxy)(foo proxy) THEN undefined # trace back # FI
-OD;
+PROC raise foo exception x = (FOOOBJECT foo)BOOL:
+  IF NOT (foo exception x mended OF foo instance)(foo instance) THEN
+    except foo exception x
+  FI

Task/Exceptions/ALGOL-68/exceptions-3.alg

@@ -1,5 +1,9 @@
-...
-except foo event:
-  IF ... THEN # Alas, cannot handle it here continue propagation of #
-    IF NOT (foo event mended OF foo base)(foo base) THEN undefined # trace back # FI
-  FI
+FOOOBJECTNEW foo instance := foo base; # exception x routines are specific to a foo #
+
+FOOMEND prior foo exception x mend = foo exception x mended OF foo;
+on foo exception x(foo instance, raise foo exception x);
+
+WHILE TRUE DO
+  # now manually raise example "foo exception x" #
+  raise foo exception x(foo instance)
+OD;

Task/Exceptions/ALGOL-68/exceptions-4.alg

@@ -1,7 +1,8 @@
-PROC raise foo event(REF OBJECTFOO foo)BOOL:
-  IF mend foo(foo) THEN
-    TRUE # continue #
-  ELSE
-    except foo event
-    FALSE # OR fall back to default event routine #
-  FI
+   on foo exception x(foo instance, prior foo exception x mend);
+... EXIT
+except foo exception x:
+  SKIP # exception x caught code here ... #
+# to continue to propagate an exception x is a bit more problematic...#
+# and requires nesting/restoring prior "raise foo exception x"#
+   on foo exception x(foo instance, prior foo exception x mend);
+   raise foo exception x(foo instance)