Thanks, Simon. For now, I've added a module with aliases for all of my class methods and law-based rewrite rules in terms of those aliases. - Conal On Tue, Nov 22, 2016 at 4:06 AM, Simon Peyton Jones wrote:

Conal

Is it possible to apply GHC rewrite rules to class methods?

Not currently. See https://ghc.haskell.org/trac/ghc/ticket/11688, esp comment:7 which gives links to similar examples. https://ghc.haskell.org/trac/ghc/ticket/10528 comment:13 gives more background.

It’d be great if someone wanted to think through all this.

Simon

*From:* Glasgow-haskell-users [mailto:glasgow-haskell-users- bounces@haskell.org] *On Behalf Of *Conal Elliott *Sent:* 17 November 2016 16:40 *To:* glasgow-haskell-users@haskell.org *Subject:* GHC rewrite rules for class operations & laws

Is it possible to apply GHC rewrite rules to class methods? From what I’ve read and seen, class methods get eliminated early by automatically-generated rules. Is there really no way to postpone such inlining until a later simplifier stage? The GHC Users Guide docs say no https://na01.safelinks.protection.outlook.com/?url=https:%2F%2Fdownloads.haskell.org%2F~ghc%2Flatest%2Fdocs%2Fhtml%2Fusers_guide%2Fglasgow_exts.html%23how-rules-interact-with-class-methods&data=02%7C01%7Csimonpj%40microsoft.com%7C8678611c4c57499f97be08d40f08662a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636149976146128136&sdata=GjkFhlWdNkT6eo85FvcLKkJYoir7Dui9xJ9kMTYKVmU%3D&reserved=0, and suggests instead giving a duplicate vocabulary with somewhat awkward names for class methods. I’ve not seen this practice in libraries. I gather that we cannot therefore use class laws as optimizations in the form of rewrite rules, which seems a terrible loss.

In Control.Category and Control.Arrow, I see rules for class laws but also header comments saying “The RULES for the methods of class Arrow may never fire e.g. compose/arr; see Trac #10528”.

I’d appreciate a reality check about my conclusions as well as any strategies for using class laws in optimization.

Thanks, -- Conal

Hi, George. Yes, please do add a task, hopefully to serve as a conversation anchor until the issues and path forward are clearer. From my perspective, class methods are among the most natural and useful candidates for rewrite rules, since they tend to have associated laws, many (but not all) of which are helpful in optimization. The alternative I know (and am using) is fairly inconvenient: replicating entire APIs just in order to delay inlining long enough to apply rules. Thanks, - Conal On Sun, Dec 11, 2016 at 7:24 AM, George Colpitts wrote:

Do you want me to add a task ticket to remove this restriction that rewrite rules can't be used for class methods?

On Tue, Nov 22, 2016 at 8:06 AM Simon Peyton Jones via Glasgow-haskell-users wrote:

...

Conal

Is it possible to apply GHC rewrite rules to class methods?

Not currently. See https://ghc.haskell.org/trac/ghc/ticket/11688, esp comment:7 which gives links to similar examples. https://ghc.haskell.org/trac/ghc/ticket/10528 comment:13 gives more background.

It’d be great if someone wanted to think through all this.

Simon

*From:* Glasgow-haskell-users [mailto:glasgow-haskell-users- bounces@haskell.org] *On Behalf Of *Conal Elliott *Sent:* 17 November 2016 16:40 *To:* glasgow-haskell-users@haskell.org *Subject:* GHC rewrite rules for class operations & laws

Is it possible to apply GHC rewrite rules to class methods? From what I’ve read and seen, class methods get eliminated early by automatically-generated rules. Is there really no way to postpone such inlining until a later simplifier stage? The GHC Users Guide docs say no https://na01.safelinks.protection.outlook.com/?url=https:%2F%2Fdownloads.haskell.org%2F~ghc%2Flatest%2Fdocs%2Fhtml%2Fusers_guide%2Fglasgow_exts.html%23how-rules-interact-with-class-methods&data=02%7C01%7Csimonpj%40microsoft.com%7C8678611c4c57499f97be08d40f08662a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636149976146128136&sdata=GjkFhlWdNkT6eo85FvcLKkJYoir7Dui9xJ9kMTYKVmU%3D&reserved=0, and suggests instead giving a duplicate vocabulary with somewhat awkward names for class methods. I’ve not seen this practice in libraries. I gather that we cannot therefore use class laws as optimizations in the form of rewrite rules, which seems a terrible loss.

In Control.Category and Control.Arrow, I see rules for class laws but also header comments saying “The RULES for the methods of class Arrow may never fire e.g. compose/arr; see Trac #10528”.

I’d appreciate a reality check about my conclusions as well as any strategies for using class laws in optimization.

Thanks, -- Conal _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users

| Indeed, we could eliminate several hundred lines of boilerplate in GHC if we | could lift this restriction. Can you be more specific? Which hundreds of lines? Do add this info to the ticket when Gorge makes it. Or just make one! Simon | -----Original Message----- | From: Ben Gamari [mailto:ben@smart-cactus.org] | Sent: 29 December 2016 14:50 | To: Conal Elliott ; George Colpitts | | Cc: glasgow-haskell-users@haskell.org; Simon Peyton Jones | | Subject: Re: GHC rewrite rules for class operations & laws | | On December 28, 2016 7:27:20 PM EST, Conal Elliott wrote: | >Hi, George. Yes, please do add a task, hopefully to serve as a | >conversation anchor until the issues and path forward are clearer. From | >my perspective, class methods are among the most natural and useful | >candidates for rewrite rules, since they tend to have associated laws, | >many (but not all) of which are helpful in optimization. The | >alternative I know (and am using) is fairly inconvenient: replicating | >entire APIs just in order to delay inlining long enough to apply rules. | > | Indeed, we could eliminate several hundred lines of boilerplate in GHC if we | could lift this restriction. | | Cheers, | | - Ben |

Done: https://ghc.haskell.org/trac/ghc/ticket/13044#ticket Not sure if it fully captures what you want so people should feel free to edit. Cheers George On Wed, Dec 28, 2016 at 8:27 PM Conal Elliott wrote:

Hi, George. Yes, please do add a task, hopefully to serve as a conversation anchor until the issues and path forward are clearer. From my perspective, class methods are among the most natural and useful candidates for rewrite rules, since they tend to have associated laws, many (but not all) of which are helpful in optimization. The alternative I know (and am using) is fairly inconvenient: replicating entire APIs just in order to delay inlining long enough to apply rules.

Thanks, - Conal

On Sun, Dec 11, 2016 at 7:24 AM, George Colpitts < george.colpitts@gmail.com> wrote:

Do you want me to add a task ticket to remove this restriction that rewrite rules can't be used for class methods?

On Tue, Nov 22, 2016 at 8:06 AM Simon Peyton Jones via Glasgow-haskell-users wrote:

Conal

Is it possible to apply GHC rewrite rules to class methods?

Not currently. See https://ghc.haskell.org/trac/ghc/ticket/11688, esp comment:7 which gives links to similar examples. https://ghc.haskell.org/trac/ghc/ticket/10528 comment:13 gives more background.

It’d be great if someone wanted to think through all this.

Simon

*From:* Glasgow-haskell-users [mailto: glasgow-haskell-users-bounces@haskell.org] *On Behalf Of *Conal Elliott *Sent:* 17 November 2016 16:40 *To:* glasgow-haskell-users@haskell.org *Subject:* GHC rewrite rules for class operations & laws

Is it possible to apply GHC rewrite rules to class methods? From what I’ve read and seen, class methods get eliminated early by automatically-generated rules. Is there really no way to postpone such inlining until a later simplifier stage? The GHC Users Guide docs say no https://na01.safelinks.protection.outlook.com/?url=https:%2F%2Fdownloads.haskell.org%2F~ghc%2Flatest%2Fdocs%2Fhtml%2Fusers_guide%2Fglasgow_exts.html%23how-rules-interact-with-class-methods&data=02%7C01%7Csimonpj%40microsoft.com%7C8678611c4c57499f97be08d40f08662a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636149976146128136&sdata=GjkFhlWdNkT6eo85FvcLKkJYoir7Dui9xJ9kMTYKVmU%3D&reserved=0, and suggests instead giving a duplicate vocabulary with somewhat awkward names for class methods. I’ve not seen this practice in libraries. I gather that we cannot therefore use class laws as optimizations in the form of rewrite rules, which seems a terrible loss.

In Control.Category and Control.Arrow, I see rules for class laws but also header comments saying “The RULES for the methods of class Arrow may never fire e.g. compose/arr; see Trac #10528”.

I’d appreciate a reality check about my conclusions as well as any strategies for using class laws in optimization.

Thanks, -- Conal _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users