Re: [Haskell-cafe] Re: Monads aren't evil? I think they are.

On Tuesday 13 January 2009 5:51:09 pm Luke Palmer wrote:

On Tue, Jan 13, 2009 at 11:21 AM, Tim Newsham wrote:

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I have seen several libraries where all functions of a monad have the

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monadic result (), e.g. Binary.Put and other writing functions. This is a clear indicator, that the Monad instance is artificial and was only chosen because of the 'do' notation.

Maybe that was the initial reason, but I've actually found the Binary.Put.PutM (where Put = PutM ()) to be useful. Sometimes your putter does need to propogate a result...

But that's the whole point of Writer! Take a monoid, make it into a monad. Put as a monad is silly.

You mean it should be Writer instead? When GHC starts optimizing (Writer Builder) as well as it optimizes PutM, then that will be a cogent argument. Until then, one might argue that it misses "the whole point of Put". -- Dan