On Sun Jul 9 20:37:23 UTC 2017, Alexis King wrote:
On Jul 9, 2017, at 10:36, Ertugrul Söylemez <esz at posteo.de> wrote:
AND PLEASE not the way an [existing proposal] suggests to do it! Please let's just do ad-hoc overloading. There is no reason to introduce new syntax, because syntax is completely orthogonal to this problem.
[existing proposal]:
Folks, that is not an existing proposal. SPJ's write-up is seductive, but fatally flawed, as Edward Kmett pointed out during the OverLoadedRecordFields development work. Quite apart from its relying on special syntax, TDNR can't cope with nested records. In:
... student.course.instructor ...
the `.course.instructor` is irresolvably ambiguous, in exactly the same way as `(show . read)`. You can maybe fix that up with FunDeps or TypeFamilies, but then you lose most of TDNR's benefits (esp not coping with existential quanted fields, which is typically a requirement to cope with OOP-style).
If I understand correctly, what youre proposing is the syntax-free variant of TDNR, which is already outlined here:
I agree that would be a very nice feature to have, and I
https://ghc.haskell.org/trac/ghc/wiki/SyntaxFreeTypeDirectedNameResolution I think everyone should read the accompanying discussion. That turned out to be not an 'outline' but just a piece of wishful thinking. It has all the flaws of the original TDNR, plus a few of its own. think doing it
without new syntax would be strongly preferable to adding new syntax. The proposal outlines the basics of how it would work, but I have no idea how difficult it would be to implement in practice.
Quite. AntC