[ghc-steering-committee] GHC2021 extensions should be sufficient for early intermediate Haskellers

[Simon Marlow]

On Thu, 17 Dec 2020 at 08:15, Spiwack, Arnaud <arnaud.spiwack at tweag.io>
wrote:

> I don't agree with this sentiment at all, to be honest. In my opinion, the
> ultimate fate of every extension is to be rolled into the standard or to be
> relegated to the bins of history. The idea of having various levels of
> languages based on how advanced they are perceived to be sounds
> extraordinary to me (also quite a bit patronising).
>
> Generally speaking, you opt in to a feature by using it. GHC2021 should
> not have features that we, as a community, don't recommend using (the
> bins-of-history ones); but, surely, TypeFamilies is not one of these. It is
> not to say that GHC2021 should have TypeFamilies, but that them being
> perceived as advanced is not, in my opinion, a relevant criterion. We
> should be asking, instead, whether it is ready.
>

I strongly agree with Arnuad here.

Cheers
Simon



>
> On Tue, Dec 15, 2020 at 10:22 PM Richard Eisenberg <rae at richarde.dev>
> wrote:
>
>> Hi all,
>>
>> In thinking about how I feel about TypeFamilies (and why I lean against
>> inclusion), I realized I had a new criterion:
>>
>> * GHC2021 extensions should be sufficient for early-intermediate
>> Haskellers
>>
>> Today, users have to enable a number of extensions just to get basic work
>> done (I'm looking at you, FlexibleContexts). So they learn just to take
>> whatever suggestion is presented to them in an error message and apply it.
>>
>> But if extensions were considered more exotic, then users might not be so
>> willing to add an extension. They would have to consider whether they
>> really want to opt into more challenging error messages and a wider
>> horizon. TypeFamilies is an extension that significantly widens the
>> horizon, but also invites new scary error messages. I think it should be
>> opt in. But this gatekeeping works only if users will be thoughtful about
>> enabling the extension; thus my new criterion.
>>
>> What do we think about this?
>>
>> (I thought of putting this on Kialo, but it didn't seem to fit the setup
>> there. Maybe I've erred in not just blasting ahead.)
>>
>> Richard
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