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 <glasgow-haskell-users@haskell.org> 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, 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