Re: [ghc-steering-committee] #493: SPECIALISE with expressions, rec: accept

Hi everyone, I believe there is broad consensus to accept this proposal. One point of detail that has arisen on the proposal thread (https://github.com/ghc-proposals/ghc-proposals/pull/493#issuecomment-1831697...) is whether to deprecate and remove the awkward and undocumented multi-type form {-# SPECIALISE f :: Int -> Int , Bool -> Bool , Float -> Float #-} since users can equally well write the clearer {-# SPECIALISE f :: Int -> Int #-} {-# SPECIALISE f :: Bool -> Bool #-} {-# SPECIALISE f :: Float -> Float #-} The current text of the proposal retains the multi-type form, but discussion on the proposal thread suggests deprecating it instead, subject to the usual requirement that if/when this is implemented, GHC will issue a warning and continue to accept the old syntax for at least 3 releases before completely removing it. I suggest we accept the proposal on the basis that it will be amended to deprecate the multi-type form. If you disagree, please object in the next week or so. Cheers, Adam On 19/12/2023 03:02, Eric Seidel wrote:

Apologies, this sounds like an obvious win. +1

On Mon, Dec 18, 2023, at 04:36, Simon Peyton Jones wrote:

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Eric, Joachim, Chris

You have not yet responded (I think) to Adam's recommendation. RSVP!

https://docs.google.com/spreadsheets/d/1e6GdwHmAjeDEUhTvP-b18MDkpTfH3SMHhFu5...

Simon

On Wed, 29 Nov 2023 at 08:25, Adam Gundry wrote:

...

Dear all,

Richard and Simon propose to generalise SPECIALISE pragmas to allow expressions, not just type signatures:

https://github.com/ghc-proposals/ghc-proposals/pull/493 https://github.com/goldfirere/ghc-proposals/blob/specialise/proposals/0000-s...

This does not add anything fundamentally new, because such SPECIALISE pragmas can be translated using the existing RULES machinery, but it does make several idioms substantially more convenient:

* Using type applications in a SPECIALISE pragma to avoid repetition

* Manual call-pattern specialisation

* Loop unrolling

Thus I propose we accept this proposal.

Cheers,

Adam

-- Adam Gundry, Haskell Consultant Well-Typed LLP, https://www.well-typed.com/ Registered in England & Wales, OC335890 27 Old Gloucester Street, London WC1N 3AX, England