On Feb 10, 2022, at 11:35 AM, Spiwack, Arnaud <arnaud.spiwack@tweag.io> wrote:
This feature, while cheap, is not free. Is the improvement worth it? I find myself doubting that Haskellers not named Richard or Vlad will start writing `f (Tuple [a, b, c])` in order to avoid writing `f (type (a, b, c))`

But what about `f (Tuple [HList [Int], Bool])`? The alternative, `f (type (HList [Int], Bool))` has a kind error: HList is expecting a list of types, not a Type. Of course, I could use a ' to get around that kind error, but that's what we're trying to get away from.

Richard

I'm happy to be convinced. But I'm not yet.

On Mon, Jan 31, 2022 at 1:26 PM Simon Peyton Jones <simon.peytonjones@gmail.com> wrote:
> Personally I’d drop TupleN/ConstraintN and accept the rest of the proposal, but I’d love to hear more opinions. Let me know what you think!

I agree.

I'm also not sure if we should have `Tuple` and `Constraints` or `Tuple` and `CTuple`. I lean to the latter.

On Sun, 30 Jan 2022 at 10:24, Vladislav Zavialov (int-index) <vlad.z.4096@gmail.com> wrote:
Dear Committee,

Richard has proposed #475 "New tuple and list syntax”. Read it here:

https://github.com/goldfirere/ghc-proposals/blob/tuple-syntax/proposals/0000-tuple-syntax.rst

Here’s some background:
Earlier we accepted #281 "Visible 'forall' in types of terms”, which introduced, among other things, the -X(No)ListTupleTypeSyntax extension. During implementation, I discovered that this part of the proposal required further design considerations. Richard has kindly agreed to take a stab at this problem, and #475 is the result.

Short summary of the proposal:
* Introduce Tuple2, Tuple3, Tuple4, and so on, as alternative ways to write the types of tuples.
* Introduce List as the alternative way to write the type of a list.
* Do the same for unboxed tuples, unboxed sums, and constraint tuples.

This is the core part of the proposal, for which I strongly urge acceptance.

There are also other minor additions:
* Rename -XListTupleTypeSyntax to -XListTuplePuns.
* Introduce Tuple [a, b, c] as a more convenient way of writing Tuple3 a b c (likewise for n/=3)
* Introduce Constraints [a, b, c] as a more convenient way of writing CTuple3 a b c (likewise for n/=3)
* Introduce TupleN a b c as another more convenient way of writing Tuple3 a b c (likewise for n/=3)
* Introduce CTupleN a b c as another more convenient way of writing CTuple3 a b c (likewise for n/=3)

I foresee that if we don’t include Tuple/Constraints, users will end up defining their own, with different libraries exporting conflicting definitions. TupleN/ConstraintN, on the other hand, seem weakly motivated.

Personally I’d drop TupleN/ConstraintN and accept the rest of the proposal, but I’d love to hear more opinions. Let me know what you think!

- Vlad
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