[Haskell-cafe] Name that function =)

Cale Gibbard cgibbard at gmail.com
Tue Dec 12 13:33:23 EST 2006

On 12/12/06, Louis J Scoras <louis.j.scoras at gmail.com> wrote:
> What I didn't realize is that even though the documentation for
> Control.Monad says that (->(r)) is an instance, it must not be defined
> there.  Importing Control.Monad.Reader indeed does make it work,
> thanks for pointing that out again.
> So I guess my next question would be, looking here
>    http://haskell.org/ghc/docs/latest/html/libraries/base/Control-Monad.html
> How do I figure out that the instance declaration is actually in the
> Reader module?  Is it just because the (->) constructor is special --
> or just not hyperlinked?

It's pretty subtle, but the Haddock there does list an instance of
MonadReader r ((->) r).

In newer GHC's the instance is also found in Control.Monad.Instances.
In my opinion, it belongs in the Prelude. :)

 - Cale

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