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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:36.0pt">
The one exception that does trip me up is MonoLocalBinds, I often have to supply a type signature when intuitively I didn't think I needed one.<o:p></o:p></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I’d like to train Haskell users to get used to MonoLocalBinds. I simply don’t know a way to give reliable, predictable
<i>type generalisation</i> (to get polymorphic types) for local bindings, in the presence of GADTs etc. I don’t think that situation is going to improve (i.e. it’s not a short term problem) … indeed it may become more pressing as the type system advances.
It’s switched on by TypeFamilies, and I think GADTs, so many of us are using it anyway.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Most local bindings are not polymorphic, so no problem; those that are probably deserve a type signature anyway. But I accept that there is a cost here: we’re giving up on generalisation for local
bindings.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">So if we are thinking about the long term future of the language, I think MonoLocalBinds will be a part of it.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> ghc-steering-committee <ghc-steering-committee-bounces@haskell.org>
<b>On Behalf Of </b>Simon Marlow<br>
<b>Sent:</b> 09 December 2020 09:11<br>
<b>To:</b> Richard Eisenberg <rae@richarde.dev><br>
<b>Cc:</b> ghc-steering-committee <ghc-steering-committee@haskell.org><br>
<b>Subject:</b> Re: [ghc-steering-committee] A plea against "fancy types" in GHC2021<o:p></o:p></span></p>
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I would like to push back here: this seems to be suggesting a fork-like situation, where we have two kinds of Haskell (fancy and non-fancy). I do feel quite strongly that we should be converging on a single language rather than creating splits. Or perhaps the
suggestion is that we don't want these extensions on by default *yet*?<o:p></o:p></p>
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Responding to Iavor's point:<o:p></o:p></p>
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> I think these extensions convey useful information about the mindset you should use when working with a specific code base, which is quite different from working with ordinary Haskell.<o:p></o:p></p>
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I personally have been working with these extensions enabled for all my code for a long time now. I'm by no means a heavy user of "fancy types", I make occasional use of type families and GADTs to solve specific problems when they arise. But I'm not even sure
what this "different mindset" is - I certainly don't feel like I have to think differently. Of course it's entirely possible that I'm just an unsophisticated user and if I understood how to think about the type system with these extensions my life would be
better!<o:p></o:p></p>
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The one exception that does trip me up is MonoLocalBinds, I often have to supply a type signature when intuitively I didn't think I needed one.<o:p></o:p></p>
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Cheers<o:p></o:p></p>
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Simon<o:p></o:p></p>
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On Tue, 8 Dec 2020 at 19:57, Richard Eisenberg <<a href="mailto:rae@richarde.dev">rae@richarde.dev</a>> wrote:<o:p></o:p></p>
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I agree with this. Fancy types are, well, fancy, and users should have to boldly declare that they're trying to be fancy.<br>
<br>
Richard<br>
<br>
> On Dec 8, 2020, at 11:46 AM, Iavor Diatchki <<a href="mailto:iavor.diatchki@gmail.com" target="_blank">iavor.diatchki@gmail.com</a>> wrote:<br>
> <br>
> Hello,<br>
> <br>
> I would like to advocate that things like `DataKinds`, `TypeFamilies`, and `GADTs` are not enabled by default in GHC2021. The reason I ask for this is that unlike many others, I think these extensions convey useful information about the mindset you should
use when working with a specific code base, which is quite different from working with ordinary Haskell.<br>
> <br>
> I do think it would be quite reasonable to have an umbrella extensions for FancyTypes too, which would enable all of those, I just don't think they should be enabled for every Haskell program.<br>
> <br>
> -Iavor<br>
> <br>
> _______________________________________________<br>
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