Re: Diagonalization/ dupe for monads and tuples?

If I really had my way, we’d make (,) a right-associative operator in both values and types, so (a, b, c) = (a, (b, c)), and accessor functions could work on any size of tuple.

uncurry . uncurry :: (a -> b -> c -> d) -> ((a, b), c) → d, so left-nesting may be more convenient. — Sent from my phone with K-9 Mail. On September 17, 2020 5:20:04 PM UTC, Jon Purdy wrote:

I’m inclined against anything to do with higher tuples than pairs, honestly. If there’s a real demand for it at some point, we can certainly consider it, but pairs are vastly more common, and I’ve only ever wanted or seen people wanting the ‘a → (a, a)’ version in practice.

Generally speaking, I see ≥3-tuples as a sign of a missing data type, and I think I’m in likeminded company here.

If I really had my way, we’d make (,) a right-associative operator in both values and types, so (a, b, c) = (a, (b, c)), and accessor functions could work on any size of tuple.

I would also expect these functions to be called dup, dup3, dup4, &c. by analogy with other tuple functions using that convention (e.g. zip, zip3).

On Thu, Sep 17, 2020, 10:03 AM David Feuer wrote:

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Does dup come with trip, quadrup, etc.? It doesn't have to, but once you plug one hole the others nearby start to stand out.

On Wed, Sep 16, 2020, 1:58 PM Carter Schonwald wrote:

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It was pointed out to me in a private communication that the tuple function \x->(x,x) is actually a special case of a diagonalization for biapplicative and some related structures monadicially. Another example in the same flavor is pure impl for the applicative instance for sized lists.

diag x = bipure x x

So framed a litttle differently, there’s definitely an abstraction or common pattern lurking here. Perhaps folks can help Tease this out. One person I chatted with this morning alluded to it being relevant to computational flavors of adjunctions or some such ? It def matters in a different way when doing computation resource aware programming in a symmetric monoidal category.

Let’s collect some ideas and patterns and get to the bottom of this! _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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