Sure, but that's relying on the promise that you're passing it a valid
BadFrog... Consider then:
deBadFrog $ BadFrogType (BadBar { badFoo = 1})
---------- Původní zpráva ----------
Od: John Wiegley
data BadFoo = BadBar{ badFoo::Int} | BadFrog{ badFrog::String, badChicken::Int}
This is fine, until we want to write a function that acts on Frogs but not on Bars. The best we can do is throw a runtime error when passed a Bar and not a Foo:
You can use wrapper types to solve this: data BadBarType = BadBarType BadFoo data BadFrogType = BadFrogType BadFoo Now you can have: deBadFrog :: BadFrogType -> String And call it as: deBadFrog $ BadFrogType (BadFrog { badFrog = "Hey", badChicken = 1}) Needless to say, you will have to create helper functions for creating Bars and Frogs, and not allow your BadBar or BadFrog value constructors to be visible outside your module. John _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe (http://www.haskell.org/mailman/listinfo/haskell-cafe)"