[ghc-steering-committee] Proposal #79 "Add a :kind!! command to ghci" — propose yes

[Richard Eisenberg]

I think this is useful, but I strongly dislike :kind!!.

Currently:

> :type <expr> gives the type of an expression, without evaluating it
> :kind <type> gives the kind of a type, without evaluating it
> <expr> evaluates an expression

Obviously, we can't have

> <type> evaluates a type

because that's terribly ambiguous.

On the thread, I proposed :eval-type, which got a less-than-lukewarm response. But I'll propose that here, regardless. Really, anything is better than :kind!! for me. (And I think we should remove :kind! too, and use a system like with have with :type +v and :type +d to have an evaluate-this-type command, with options.)

Richard

> On Mar 20, 2018, at 10:42 PM, Manuel M T Chakravarty <chak at justtesting.org> wrote:
> 
> We need to decide on the Proposal #79 ”Add a :kind!! command to ghci, to expand type families and type synonyms”:
> 
>  (rendered)   https://github.com/alpmestan/ghc-proposals/blob/master/proposals/0000-kind-bang-bang.rst
>  (discussion) https://github.com/ghc-proposals/ghc-proposals/pull/79
> 
> I agree that this is useful functionality and it is a simple change to GHCi. There has been some discussion about the naming of this command, but TBH I didn’t find any of the alternatives more convincing than ”:kind!!”, so I’d suggest to stick with that. 
> 
> I favour accepting this proposal. Are there any dissenting opinions?
> 
> Cheers,
> Manuel
> 
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