Re: [Haskell-cafe] ListT considered harmful

On Fri, Mar 27, 2015 at 5:07 PM, Michael Snoyman wrote:

I'm in favor of deprecation, but opposed to removing any time soon due to backwards compatibility concerns.

I agree. Given that we just deprecated ErrorT (which is both more popular, and does follow the monad laws) I think there is good reason to phase out transformers' ListT as well. I've attached a patch that adds the relevant pragma. I'm not familiar with darcs so excuse me if it's messed up :) libraries list and/or Ross Paterson, do you have anything to say about this issue?

On Fri, Mar 27, 2015 at 7:03 AM Fumiaki Kinoshita wrote:

...

It is well known that ListT m in transformers is not a monad unless the underlying monad is commutative. The fact that ListT is not a monad transformer is sufficient to remove it from the package, and several packages already defined their own ListT.

Oughtn't we deprecate ListT or replace it by a correct one? _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

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