Re: Help needed: Restrictions of proc-notation with RebindableSyntax

Simon, Richard, thank you for your answer! I don't have time to look into the GHC sources right now, but I will set aside some time after the holidays and take a close look at what the exact restrictions on proc-notation are and document them. Since you suggested a rewrite of GHC's handling of proc-syntax, are there any opinions on integrating generalized arrows (Joseph 2014) in the process? I think they would greatly improve arrows! I don't know if I have the time to attempt this, but if I find the time I would give it a try. Why wasn't this integrated while it was still actively developed? Best, Jan [Joseph 2014] https://www2.eecs.berkeley.edu/Pubs/TechRpts/ 2014/EECS-2014-130.pdf 2016-11-29 12:41 GMT+00:00 Simon Peyton Jones :

Jan,

Type checking and desugaring for arrow syntax has received Absolutely No Love for several years. I do not understand how it works very well, and I would not be at all surprised if it is broken in corner cases.

It really needs someone to look at it carefully, document it better, and perhaps refactor it – esp by using a different data type rather than piggy-backing on HsExpr.

In the light of that understanding, I think rebindable syntax will be easier.

I don’t know if you are up for that, but it’s a rather un-tended part of GHC.

Thanks

Simon

*From:* ghc-devs [mailto:ghc-devs-bounces@haskell.org] *On Behalf Of *Richard Eisenberg *Sent:* 28 November 2016 22:30 *To:* Jan Bracker *Cc:* ghc-devs@haskell.org *Subject:* Help needed: Restrictions of proc-notation with RebindableSyntax

Jan’s question is a good one, but I don’t know enough about procs to be able to answer. I do know that the answer can be found by looking for uses of `tcSyntaxOp` in the TcArrows module.... but I just can’t translate it all to source Haskell, having roughly 0 understanding of this end of the language.

Can anyone else help Jan here?

Richard

On Nov 23, 2016, at 4:34 AM, Jan Bracker via ghc-devs < ghc-devs@haskell.org> wrote:

Hello,

I want to use the proc-notation together with RebindableSyntax. So far what I am trying to do is working fine, but I would like to know what the exact restrictions on the supplied functions are. I am introducing additional indices and constraints on the operations. The documentation [1] says the details are in flux and that I should ask directly.

Best,

Jan

[1] https://downloads.haskell.org/~ghc/latest/docs/html/ users_guide/glasgow_exts.html#rebindable-syntax-and-the- implicit-prelude-import https://na01.safelinks.protection.outlook.com/?url=https:%2F%2Fdownloads.haskell.org%2F~ghc%2Flatest%2Fdocs%2Fhtml%2Fusers_guide%2Fglasgow_exts.html%23rebindable-syntax-and-the-implicit-prelude-import&data=02%7C01%7Csimonpj%40microsoft.com%7C80e472cedf78463bd18408d417de1af5%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636159690104764444&sdata=ygqePSmgcPKnPmKDBfZplkyjG9BIDBO1L1MWHNpqw88%3D&reserved=0

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