Re: es %dup

[Scott Schwartz <schwartz@groucho.cs.psu.edu>]

| The case in question involves re-defining unit 0, which isn't something
| for which you could substitute re-defining any arbitrary unused descriptor.
| I start with unit 0 open on a streams pipe, and need to have the tty open
| on 0 before executing interactive commands.

Yes, but those are all special cases that can be handled by a more
general scheme.  It's the meaning of syntactic sugar that is under
discussion.  I thought you were suggesting that ``exec <foo'' should
mean  ``push foo onto input'', as opposed to ``set input to foo''. 
(I think there should be two operators for those two concepts.)
When you wrote

	``So, after the "exec <foo", an application
	invoked by es should find "ls" on its input
	stream, but the next es command still should come
	from the original command input stream.''

I interpreted that as asking for something like setting a default 
redirection on future commands, something analgous the common-lisp

	(with-open-file (*standard-input* "foo")
		(my-cat)
	)

Is that right?

| I have to admit I don't know how perl and tcl would deal with this issue,
| so I'm unable to picture exactly what kind of functionality you mean.

They can do what you can do in C.  You should have direct access to
open, close, read, write, etc.