Dynamic scoping

Anthony Hannan ajh18 at cornell.edu
Thu Jan 30 23:38:59 UTC 2003

Attached is another version of my dynamic scoping and replaces the
previous one I sent out a couple of days ago.  It now looks like:

	[self bar] on: #world do: [myWorld].

	thisContext outer world.

No more separate handler class and no multi-method handler.  To handle
mutliple messages, you must nest mulitple on:do: blocks.  I have found
that most of the time only one handler method is needed per protected
block.  I have overloaded the on:do: method for efficiency with
exception handling and because of its like semantics (so its really not
overloading).  "on: exceptionClass do: block" still works as before.  In
either case a message is sent to the #outer of a context, which is the
closest #on:do: context sender wrapped in a ContextHandler.  The message
is an arbitrary message like #world above, or it is #handleSignal: if an
exception is signaled.  The contextHandler responds to #handleSignal:
(or the arbitrary message) by executing the do: block if the on: arg
handles the exception (or equals the message selector), otherwise it
forward the message to its outer #on:do: context.  If no more #on:do:
contexts exist in the sender chain then a DefaultContextHandler is
created and sent the message.  It calls #defaultAction on the exception
(or signals MessageNotUnderstood on the general message).

I will be including these changes with my closures-for-stock-vm package
coming soon.

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