Specialized type hints

[Christopher Allen]

I was looking for an indication that a more general type error improvement
sweep would be welcome. I could pinpoint a particular type error if you
liked (such as the one that prompted this email), but there are general UX
improvements I would like to undertake.

On Fri, Mar 4, 2016 at 4:25 AM, Simon Peyton Jones <simonpj at microsoft.com>
wrote:

> Christopher
>
>
>
> Improving error message is an excellent goal, and one that I have spent
> more hours on than I care to tell you.
>
>
>
> If you have a particular one in mind, could you open a Trac ticket with a
> particular reproducible test case, the error message you get, and the error
> message you’d like to get.
>
>
> Thanks
>
>
>
> Simon
>
>
>
> *From:* ghc-devs [mailto:ghc-devs-bounces at haskell.org] *On Behalf Of *Christopher
> Allen
> *Sent:* 03 March 2016 07:55
> *To:* ghc-devs at haskell.org
> *Subject:* Specialized type hints
>
>
>
> I'd like to see how warm people would be to catching GHC's type error
> quality up a bit.
>
>
>
> I did a write-up on a confusion a reader of our book had:
>
>
>
> https://gist.github.com/bitemyapp/c27c721b92dab0248433
> <https://na01.safelinks.protection.outlook.com/?url=https%3a%2f%2fgist.github.com%2fbitemyapp%2fc27c721b92dab0248433&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7c64d227da349847f85fe308d343391dbb%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=EtjujRikMvoUN%2fBq6RtOrotsPdXdvZggnMU3Cu2BypE%3d>
>
>
>
>
> This is not new. A lot of people complain about this particular type error
> in particular when they say GHC has bad type errors. I don't think GHC's
> type errors are bad, but I do think they could be improved and this
> particular issue has an unfortunate source to sink distance.
>
>
>
> I would rather type error improvements not be buried behind a "silly
> beginners only" flag and that they just be part of improving the UX for
> everyone. With that proviso, how likely would specialized type error hints
> and some general error message fix ups be regarded?
>
>
>
> By specialized I mean, "detect that they tried to find an instance of Num
> for (-> something something) and suggest that they did the wrong thing,
> with possible fixes: X Y Z". Ideally before the "hey do you want
> FlexibleContexts?!" thing fires.
>
>
>
> I do not think I am capable of doing this, but being able to zoom in,
> clang style, to the expression where they are (probably accidentally) using
> a function like a Num or a Num like a function would be pretty valuable so
> they don't have to guess-n-check parenthesize their code.
>
>
>
>
>
> --
>
> Chris Allen
>



-- 
Chris Allen
Currently working on http://haskellbook.com
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