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, Pierre 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
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe