[Haskell-cafe] Basic question....

rodrigo.bonifacio rodrigo.bonifacio at uol.com.br
Fri Aug 17 09:11:21 EDT 2007

Hi all.

I want to create the following polymorphic type (EnvItem) that we can apply two functions (envKey and envValue). I tried the following:

> type Key = String

> data EnvItem a = EnvItem (Key, a)

> envKey :: EnvItem (Key, a) -> String
> envKey EnvItem (key, value) = key

> envValue :: EnvValue(Key, a) -> a
> envValue EnvItem (key, value) = value

But this is resulting in the error: [Constructor "EnvItem" must have exactly 1 argument in pattern]

I think this is a very basic problem, but I don't know what is wrong.



More information about the Haskell-Cafe mailing list