Regular expressions as Haskell Type Generators?

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