[boost] [spirit] scan_keyword: scan an InputIterator for a keyword.

Subject: [boost] [spirit] scan_keyword: scan an InputIterator for a keyword.
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2011-11-28 16:45:31

Hi,

for chrono input I'm using a scan_keyword function  that adapted from 
libc++ library (you can find the code in[1]).
Next follows the interface:

// scan_keyword
// Scans [b, e) until a match is found in the basic_strings range
//  [kb, ke) or until it can be shown that there is no match in [kb, ke).
//  b will be incremented (visibly), consuming CharT until a match is found
//  or proved to not exist.  A keyword may be "", in which will match 
anything.
//  If one keyword is a prefix of another, and the next CharT in the input
//  might match another keyword, the algorithm will attempt to find the 
longest
//  matching keyword.  If the longer matching keyword ends up not 
matching, then
//  no keyword match is found.  If no keyword match is found, ke is returned
//  and failbit is set in err.
//  Else an iterator pointing to the matching keyword is found.  If more 
than
//  one keyword matches, an iterator to the first matching keyword is 
returned.
//  If on exit b == e, eofbit is set in err.
//  Examples:
//  Keywords:  "a", "abb"
//  If the input is "a", the first keyword matches and eofbit is set.
//  If the input is "abc", no match is found and "ab" are consumed.

template <class InputIterator, class ForwardIterator>
ForwardIterator
scan_keyword(InputIterator& b, InputIterator e,
                ForwardIterator kb, ForwardIterator ke,
                std::ios_base::iostate& err
                );

What is the better way to do that (or something similar) with Spirit/Lexer?
Can we hope that the Spirit solution could perform much better?
What about if the strings to parse are know at compile-time?

[1] 
https://svn.boost.org/svn/boost/trunk/boost/chrono/detail/scan_keyword.hpp

Best,
Vicente