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From: Maurizio Vitale (mav_at_[hidden])
Date: 2007-04-26 18:08:24

Eric Niebler <eric_at_[hidden]> writes:

> No, proto::_ is a placeholder. And proto::not_<> can logically negate
> any grammar, not just proto::_.

FWIW I kind of like proto::_. It gives me warm memories of ML and Haskell patterns
in the land of...brrr...I digress.

But I'd appreciate if you could elaborate on why you see it as a placeholder.

Technically I guess it is: it certainly takes space in the parse tree, but I tend to
think about placeholders as things that mark a spot that I can then reference
from somewhere else (and from here stems my confusion on transformations from
another thread. This and the fact that mpl lambda placeholders are mentioned in
the documentation).

Now I see proto::_ more like a wildcard pattern that matches anything but doesn't
have additional meaning (or features for the user).

Is there anything I'm missing about proto::_ ?

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