[Haskell-cafe] creating a type based on a string

Pierre-Etienne Meunier pierreetienne.meunier at gmail.com
Thu Sep 2 20:21:11 EDT 2010

You may also look at Data.Dynamic / Data.Typeable. It may not work really well, depending on how you defined A and B. In GHC, it should work with any type produced with the haskell 98 use of the keyword "data", though.

This is the "canonical" solution to cope with the GHC API returning values of arbitrary type.

Good luck,

El 02/09/2010, a las 16:31, Andrew U. Frank escribió:

> I have a user input (string) and need to select one of two types.
> depending what the input is. is this possible? 
> data A
> data B 
> data X n = X String
> op :: String -> X n
> op "a" = X "a" :: X A
> op "b" = X "b" :: X B
> this does obviously not compile. is there a way to achieve that the type
> X A is produced when the input is "a" and X B when the input is "b"?
> thank you for help!
> andrew
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