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From: joel de guzman (isis-tech_at_[hidden])
Date: 2001-06-01 11:28:14

From: "Vladimir Prus":

> I think that it is possible to write a metaprogram that will take a
> expression tree and reparse it assuming whatever precedece you like.
> This is not easily done, though. I actually think that we need some
> metalanguage, most likely functional, which will be mapped to template
> metaprograms. But this is not easily done as well.

I spent an hour thinking about this if it is indeed possible. I'd say now
it isn't. Here's the reason:

an expression:

   a, (b | c).... explicit grouping

which explicitly groups (b | c) cannot be distinguished, using any meta-
programming techniques, from:

   a, b | c.... implicit grouping (precedence groups (b | c) automatically)

The problem is that we cannot overload the parentheses () for
grouping. There's no way to know whether the user typed the
first or the second expression.

Joel de Guzman

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