No, with exactly the type signatures they have I don't think you can. But the untyped version of them can be implemented. And that is good enough to convince me that the beta rule is still valid.
-- Lennart
Josef Svenningsson wrote:
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Marcin 'Qrczak' Kowalczyk Sent: den 25 november 2004 11:49 To: [EMAIL PROTECTED] Subject: Re: [Haskell] Real life examples
Lennart Augustsson <[EMAIL PROTECTED]> writes:
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.
I think neither of them can.
I agree with Marcin. I challenge you (Lennart) to write Control.Monad.ST in Haskell98. I (and many others) have tried and failed. An interesting summary by Koen can be found here: http://www.haskell.org/pipermail/haskell/2001-September/007922.html
Cheers,
/Josef
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