[Haskell-cafe] Re: Transformers versus monadLib versus...

Ertugrul Soeylemez es at ertes.de
Tue Jul 6 11:02:54 EDT 2010

Yves Parès <limestrael at gmail.com> wrote:

> Yes but, for instance, every library which provides monad transformers
> will provides a MTL's MonadTrans instance, not a monadLib's MonadT
> instance.  And since a library hides its types internals, you cannot
> write the MonadT instances yourself.
> For instance, I was planning to translate a little program of mine
> (which uses quite heavily monad transformers) to monadLib. It uses the
> packages operational which is based on MTL, and I cannot make myself
> operational's transformers instances of MonadT.
> How would you solve that?

You don't, unfortunately.  I would probably use both mtl and monadLib or
even rewrite 'operational' to support monadLib.

> (btw, I like the fact that monadLib provides IdT ^^ (IdentityT))

Haven't found a use for it though. =)


nightmare = unsafePerformIO (getWrongWife >>= sex)

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