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

[Gregory Crosswhite]

  What is stopping you from using an enumeration type?

data Tag = A  | B
data X = X String Tag

op "a" = X "a" A
op "b" = X "b" B

On 9/2/10 1:31 PM, Andrew U. Frank wrote:
> 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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