Ben Rudiak-Gould wrote:
Lennart Augustsson wrote:
> What do you mean when you say the interface is pure?
>
> If your module is really pure then there should be an implemenation
> of it (which could have really bad complexity) with the same observable
> behaviour that uses only pure Haskell. Is this possible?
Really? I agree with the converse of that statement, but I don't think
it goes both ways. To me a function or module is pure when you can use
it without compromising the equational properties of the language. I
don't think Data.Dynamic or Control.Monad.ST satisfy your criterion for
purity, but I would call them pure (after discarding the functions
marked unsafe in the latter).
Agreed, there can pure functions that cannot be written with the pure
primitives, but then you have a proof obligation. An "easy" way to
prove it is to provide an equivalent implementation that uses only
pure functions. As far as I remember Control.Monad.ST can be written
purely. And I think the same is true for Data.Dynamic.
-- Lennart
_______________________________________________
Haskell mailing list
[EMAIL PROTECTED]
http://www.haskell.org/mailman/listinfo/haskell
