Tentative high-level plans for 7.10.1

[Thomas Winant]

On 2014-10-08 00:21, Simon Peyton Jones wrote:
> Is the wiki page up to date?
> https://ghc.haskell.org/trac/ghc/wiki/PartialTypeSignatures

Yes it is.


> I'd move the Constraint Wildcards bit out to an appendix or delete
> altogether -- it's a distraction since it's not part of the design.
> 
> Named wildcard are described as a "fourth form" but actually it's
> "third" I suppose. And aren't they just a vairant of "type wildcards"?
>  You can't name "extra-constraint wildcards" can you?
> 
> There's a long section on "partial expressions and pattern signatures"
> but I think the conclusion is "we don't do this".  Again, move to an
> appendix of not-implemented ideas.
> 
> Try to focus on the actual design.
> 
> Thanks!

Done.


Cheers,
Thomas



> ________________________________________
> From: ghc-devs [ghc-devs-bounces at haskell.org] on behalf of Thomas
> Winant [Thomas.Winant at cs.kuleuven.be]
> Sent: 07 October 2014 17:07
> To: ghc-devs at haskell.org
> Subject: Re: Tentative high-level plans for 7.10.1
> 
> Hi,
> 
> On 2014-10-03 23:35, Austin Seipp wrote:
>> ..
>> Here are the major patches on Phabricator still needing review, that I
>> think we'd like to see for 7.10.1:
>> 
>>   - D168: Partial type signatures
>> ..
> 
> As Austin said, our patch implementing Partial Type Signatures is still
> up for code review on Phabricator [1]. It is our goal too to get it in
> 7.10.1, and we will try to do as much as we can to help out with this
> process.
> 
> We'd like it very much if people had a thorough look at it (thanks
> Richard for the feedback). We're glad to provide additional info
> (including extra comments in the code), rewrite confusing code, etc.
> 
> = Status =
> 
> The implementation is nearly complete:
> * We've integrated support for Holes, i.e. by default, an underscore in
>    a type signature will generate an error message mentioning the
>    inferred type. By enabling -XPartialTypeSignatures, the inferred 
> type
>    is used and the underscore can remain in the type signature.
> * SPJ's proposed simplifications (over Skype) have been implemented,
>    except for the fact that we still use the annotated constraints for
>    solving, see [2].
> * Richard's comments on Phabricator [1] have been addressed in extra
>    commits.
> * I've rebased the patch against master on Monday.
> * I've added docstring for most of the new functions I've added.
> * Some TODOs still remain, I'll summarise the most important ones here.
>    See [3] for a detailed list with examples.
>    * When -XMonoLocalBinds is enabled (implied by -XGADTs and
>      -XTypeFamilies), (some) local bindings without type signature 
> aren't
>      generalised. Partial type signatures should follow this behaviour.
>      This is currently not handled correctly. We have a stopgap 
> solution
>      involving generating an error in mind, but would prefer a real 
> fix.
>      We'd like some help with this.
>    * Partial type signatures are currently ignored for pattern 
> bindings.
>      This bug doesn't seem to be difficult to solve, but requires some
>      debugging.
>    * The following code doesn't type check:
> 
>      {-# LANGUAGE MonomorphismRestriction, PartialTypeSignatures #-}
>      charlie :: _ => a
>      charlie = 3
> 
>      Type error: No instance for (Num a) arising from the literal ‘3’. 
> We
>      would like the (Num a) constraint to be inferred (because of the
>      extra-constraint wildcard).
>    * Some smaller things, e.g. improving error messages.
> 
> We'll try to fix the remaining TODOs, but help is certainly appreciated
> and will speed up integrating this patch!
> 
> Please have a look at the code and let us know what we can do to help.
> 
> 
> Cheers,
> Thomas Winant
> 
> [1]: https://phabricator.haskell.org/D168
> [2]:
> https://ghc.haskell.org/trac/ghc/wiki/PartialTypeSignatures#extra-constraints-wildcard
> [3]: https://ghc.haskell.org/trac/ghc/wiki/PartialTypeSignatures#TODOs
> 
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