From: Hans Aberg (firstname.lastname@example.org)
Date: Sat Oct 13 2007 - 16:11:03 CDT
On 13 Oct 2007, at 21:36, Philippe Verdy wrote:
> ...such operation is typically used in association with [an] operator
> that restricts the set of matchable strings.
You might merely add operations that correspond to the set operations
of the languages, and let the user figure out their usability. L(x|y)
is already the union of L(x) and L(y). And if, for a natural number
k, L(x^k) = L(x)^k, then one can extract all strings of length k to
complement against (see below).
So let L(x&y) be the intersection of L(x) and L(y), L(~x) the set
complement of L(x), L(x \ y) = L(x) \ L(y) (set difference).
Then, if "." matches all characters, all strings of length 2 that do
not match "ab" can be gotten from .^2 \ "ab" (or .^2 & ~"ab"). If U
is the set of legal Unicode strings, and U_k the subset of strings of
Unicode length 2 (which might be different from the string length),
then all Unicode strings of Unicode length 2 that do not match "ab"
can be gotten from U_2 \ "ab".
Mostly, one would use the set difference \ operator, rather than the
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