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Subject: Re: [Boost-users] [Proto] Extracting types of sub-expression in transform
From: Eric Niebler (eric_at_[hidden])
Date: 2008-10-19 01:16:38

van Godard wrote:
> The canonical way to incorporate typing (including much richer type
> systems than this) in a formal grammar is through van Wijngaarden
> grammars. See It is possible to
> generate both the parser and type analysis from such a grammar, and
> compilers that do so still exist.
> Sadly, there is no Boost VWG library. Perhaps you'll write one?

I hadn't even considered the notion of a type system for a DSEL, but it
makes perfect sense. Unfortunately, the only tutorial I found for van
Wijngaarden grammars is here:

Perhaps it's because I'm tired, but I'm not making heads or tails of it
at the moment. Can you point me to a gentler introduction?

(Way back when I started with expression templates, I thought that
calling them an "embedded language" was just a cute metaphor, but much
can be gained from taking the serious view that these really *are*
languages, deserving of grammars, semantic actions, ... type systems,
too. Once we fully embrace that view, there's decades worth of
programming language theory we can leverage.)

Eric Niebler
BoostPro Computing

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