[Haskell-cafe] why OverloadedTuples extension is missing?

[Carter Schonwald]

In some respects, there’s another path: further generalizing overloaded
lists with the right machinery for list syntax to support hlists and sized
lists!

I prototyped out a possible type class for this that predates pattern
synonyms and I believe it could be made even nicer with pattern synonyms

https://github.com/cartazio/HetList/blob/master/HetList.hs

Here’s the example code above!

On Thu, Jan 13, 2022 at 8:06 PM Viktor Dukhovni <ietf-dane at dukhovni.org>
wrote:

> On Thu, Jan 13, 2022 at 07:50:02PM -0500, Jeffrey Brown wrote:
> > You can get very close -- specifically, to within two extra characters --
> > to the brevity you're imagining without introducing any new extensions:
> >
> >     data Foo = Foo Int Int
> >       deriving (Show)
> >
> >     f :: (Int, Int) -> Foo
> >     f = uncurry Foo
> >
> >     g :: Int -> Int -> Foo
> >     g = Foo
>
>     {-# LANGUAGE PatternSynonyms #-}
>
>     pattern F :: Int -> Int -> Foo
>     pattern F f s = Foo f s
>
> Which abbreviates a frequently used constructor, and works in pattern
> matches too.
>
>     λ> case F 4 "2" of { F x y -> show x ++ y }
>     "42"
>
> But the original question is really about logical completeness of
> overloading primitives, not about work-arounds, so bottom line I too
> don't think that overloading tuples is justified, since this breaks
> extensibility if constructor type signatures later become ambiguous, I
> don't think the idea has sufficient merit.
>
> --
>     Viktor.
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