[Haskell-cafe] Language complexity & beginners (Was: New type of ($) operator in GHC 8.0 is problematic)

Mihai Maruseac mihai.maruseac at gmail.com
Sat Feb 6 00:27:42 UTC 2016

On Fri, Feb 5, 2016 at 7:09 PM, Richard Eisenberg <eir at cis.upenn.edu> wrote:
> Another great question that has come up is about Haddock output (Hackage). I
> think Haddock needs to add a facility where library authors can include
> specializations of an overly general type. This can be done in commentary,
> but it's not as prominent. Such a new feature would address the ($) problem,
> as ($) :: forall (a :: *) (b :: *). (a -> b) -> a -> b is a specialization
> of its real type. It would also help a great deal with FTP-related
> generalizations.

This goes hand in hand with Artyom's suggestion of a warning in GHCi
after showing the simpler type.

I'm thinking of a flag which enables/disables printing the simplest
type with warning (in GHCi) or footnote (or otherwise, in Haddock). We
can have the default behavior of the flag be either printing the
simpler type + extra (warning/footnote) or printing the longer type
and include a reference in our learning materials that beginners and
people confused by the long, complex and real type, can use
--use-simpler-types flag.

Mihai Maruseac (MM)
"If you can't solve a problem, then there's an easier problem you can
solve: find it." -- George Polya

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