Regular expressions as Haskell Type Generators?

[Steffen Mazanek]

Hello,

I am wondering if it would be worth while (and possible) to allow the
definition of types by regular expressions, e.g.

data Date = Date #RegExp([0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9])

or easier with some auxiliary constructs.
Clearly there would be some drawbacks with the use of standard 
String-operations or type checking. But in praxi it may be
absolutely relevant. 
Or is some work already done in this direction?

Ciao,
Steffen