Re: additional regular expression operators

Ralph Boland <rpboland@gmail.com> writes:
>I have never found a useful example of set intersection though.


FP numbers are typically strings of digits and decimal points that
contain at least one digit and exactly one decimal point. That's a
little more elegant to describe as intersection than as a union; let's
use '&' as intersection operator:


[.0-9]*&.*[0-9].*&[^.]*[.][^.]*


That reflects exactly the specification above, which is not so clear
with the equivalent


[0-9]+[.][0-9]*|[.][0-9]+


Intersections can also be used for a set of things in arbitrary order
and also for a subset of things. For a set (i.e., your R @ S @ T):


(R|S|T)*&R~*RR~*&S~*SS~*&T~*TT~*


For a subset:


(R|S|T)*&R~*R?R~*&S~*S?S~*&T~*T?T~*


- anton
--
M. Anton Ertl
anton@mips.complang.tuwien.ac.at
http://www.complang.tuwien.ac.at/anton/

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