I think it's a matter of funding and interest. A lot of developers[1] would love to see better search lexing in Koha[2], but the cost would be rather high, as it requires a more-or-less complete rewrite of the searching code in order to work, and my impression is that the searching works well enough for most people that it just isn't a priority for most organizations funding Koha development. That said, I am in complete agreement that not having a flexible search lexer in Koha is a serious omission[3].
I agree also. Ideally, we should define for Koha a query language syntax in BNF: http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form and then, create a query parser, which would validate queries, and transform them into Zebra native syntax (3 indeed, PQF, CCL, CQL), or transform them into coming SolR query syntax. A standard Perl module like Regexp::Grammars could help to do the job. -- Frédéric DEMIANS http://www.tamil.fr/u/fdemians.html