On 08/01/06, Brian Hulley <[EMAIL PROTECTED]> wrote:
> For example, suppose I'm writing a module M that deals with grammar, where
> the elements in a grammar rule are parameterised so that rules can be
> written using strings but processed as if we'd used ints instead:
>
> data Element a = Terminal a | Nonterminal a | Action a
>
> data Rule a = Rule (Element a) [[Element a]]
>
> Now I want to convert elements and rules from a to Int, so at the moment I
> have to write:
>
> convertElement :: Element a -> CM (Element Int)
> ...
>
> convertRule :: Rule a -> CM (Rule Int)
>
> for some appropriate monad CM.
> Whereas I would have much preferred to use just the word "convert" in both
> cases. It is tremendously annoying to have to suffix everything with the
> type name.
This is what typeclasses are for.
class Convert c where
convert :: c a -> CM (c Int)
- Cale
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