[Haskell-cafe] Diving into the records swamp (possible GSoC project)

Petr Pudlák petr.mvd at gmail.com
Fri Apr 26 20:53:19 CEST 2013

Hi Adam,

very nice idea. As the others, I'm curious why you chose to implement SORF
in favor of the other ideas?

I just read the SORF proposal, and I'm a bit concerned about what error
messages would GHC issue when someone would type incorrect code involving
such records. Currently Haskell's error messages already pose a barrier for
newcomers (like "No instance for (Num (a -> a))"), and if records are
converted into those very complicated `Has` instances, type errors would be
probably undecipherable even for moderate skilled Haskell users.
Considering that records are a basic feature of Haskell and something that
 people with OOP background are familiar with, this could result in a
feature that would without doubts deter many (if not most) newcomers. So do
you think it would be possible to implement it in such a way that users get
sensible type error messages?

  Best regards,

2013/4/26 Adam Gundry <adam.gundry at strath.ac.uk>

> Hi,
> I am hoping to do a GSoC project this year working on GHC, and have been
> pointed in the direction of the records issue (in particular, the desire
> to overload field names). This has been discussed on-and-off for years,
> and while there are lots of ideas [1], little has been implemented in
> GHC itself.
> The plan would be to implement a solution to the "narrow issue" of
> overloaded field names, along the lines of Simon PJ's SORF proposal (on
> the wiki). This would provide a basis for experimentation with
> first-class record types. While there are still design issues to
> resolve, the broad plan is clear and I'm confident it can be implemented
> in a summer and without overly restricting future record system designs.
> Does this sound like a reasonable strategy? I'd appreciate comments and
> criticism, although arguing about the details of the design should
> perhaps wait.
> (A little about me: I'm a PhD student working on type inference for
> Haskell and dependent types, with about four years' Haskell experience
> including work on big type-system related projects. I am familiar with
> the theory behind GHC, but I haven't worked on the code before.)
> Thanks,
> Adam Gundry
> [1] http://hackage.haskell.org/trac/ghc/wiki/Records
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