[ghc-steering-committee] #179: Tweak the printing of foralls, recommendation: accept

[Iavor Diatchki]

Overall I am all for simplifying this stuff, but the bit where constraints
with no variables are not simplified seems quite confusing.   More
concretely, using the example from the proposal:

bar :: forall a b. (a ~ Int) => a -> b -> a

Is it the case that `:t bar @Bool` will print

bar :: (Bool ~ Int) => Bool -> b -> Bool

This looks particularly confusing without the explicit `forall`, although
it seems questionable either way.

-Iavor



On Thu, Mar 14, 2019 at 7:47 AM Joachim Breitner <mail at joachim-breitner.de>
wrote:

> Dear Committee,
>
> Richard, in collarboration with Simon PJ, proposes some tweaks to how
> foralls are printed by GHC.
>
> In particular, whenever a type variable is printed with an forall, it
> is printed with {a} unless it is a specified variable. And there are
> tweaks to what :type does with its argument that makes it more useful,
> and obviates the need for a separate :type +v.
>
> https://github.com/goldfirere/ghc-proposals/blob/printing-foralls/proposals/0000-printing-foralls.rst
>
> I like that it actually simplifies the UI (by removing :type +v), so I
> recommend acceptance.
>
> Cheers,
> Joachim
> --
> Joachim Breitner
>   mail at joachim-breitner.de
>   http://www.joachim-breitner.de/
>
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