[UPHPU] regex creator?

[Daniel C.]

Ash's thread got me thinking - how hard would it be to make a regex
creator?  You'd enter all the things you want it to match, one per
line, and the script automatically generates the regex for you.  In
Ash's example your input would look like this:

A-z
0-9
,
(
)
'
:
.

Putting something like that together should be trivial (shouldn't it?)
but I've never heard of one in all of the discussions of regexes that
have come up.  Is there a reason nothing like this exists, other than
that no-one has bothered?  Have I fundamentally misunderstood regexes
in some way?

Dan