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From: John Max Skaller (skaller_at_[hidden])
Date: 2001-07-26 15:30:01

John Maddock wrote:

> Yep, although its not the backtracking as such that mandates this - if you
> want to be able to return iterators denoting what matched then they have to
> be at least forward iterators in any case. The only reason that
> bidirection iterators are required is to make it easier to match things
> like $ and ^, in some cases.

        It is possible to build interator category adaptors:

        input->forward -> bidirectional -> random

There are also some interesting non-standard iterator categories,
for example: 'anchored bidirectional iterator' which is a pair
consisting of a forward iterator (the anchor) and a bidirectional
iterator which can't move backwards past the anchor.
By using an input->forward iterator adaptor for the anchor,
you can write a parser which provides bidirectional iterators
for look ahead, but actually uses an _input_ iterator
to get source tokens.

        Are there any such 'category adaptors' in boost?
Any interest?

John (Max) Skaller, mailto:skaller_at_[hidden] 
10/1 Toxteth Rd Glebe NSW 2037 Australia voice: 61-2-9660-0850
New generation programming language Felix
Literate Programming tool Interscript

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