> On 8 Sep 2017 at 07:54 Nathan van Doorm wrote: Thank you Nathan and Mario for your explanations.
> The motivation is that there are many types with sensible > definitions for addition and multiplication etc that can't > be instances of Eq or Show, for example functions to > numbers (allowing us to write "sin + cos" instead of "\x > -> sin x + cos X") or arbitrary real numbers (where > comparison isn't necessarily computable). The Haskell 2010 report section 6.4 Numbers starts: "Haskell provides several kinds of numbers; ...". Then goes on to class `Num`. Functions `sin`, `cos` are not numbers, so it's not sensible to put them in `Num`. By the same token, I wouldn't expect Haskell to figure out tan == sin / cos so it's not sensible to put those in `Eq`. If you want to write higher-order algebraic expressions with the Num operators, override the Prelude. (Perhaps this is part of a wider issue to do with reorganising `Num` so it has nicer 'mathematical' structure: additive, multiplicative, etc. That might also cover that `Eq` is dodgy for floating-point or `Rational`s representations. But that reorg has seemed prohibitively hard.) > > I'm not sure why this is being discussed on the mailing > list rather than the Github proposals thing, ... Quite. I've found the github proposals process for GHC very valuable. > but I do know that that has grown somewhat inactive The Haskell-prime list has been fairly inactive too. It was originally formed to identify stable features, that were to go into a revised language standard that was to be an evolution from H98. "Haskell' will be a conservative refinement of Haskell 98." it still says on the listinfo. (Note the future tense.) That process ended with the H2010 report. I must admit I thought (wrongly, it seems) that Haskell-prime rather died after that. Somebody could start by loading up the outstanding proposals from the Haskell-prime list. (Herbert says this one is from 2011.) > and this is as good as anything for getting the > Haskell' committee to make a final judgement. > Do we need any judgment at all? The skies do not seem to be falling. > This has been how it is in GHC for a long time now, > so it really is a matter for the Haskell' committee > rather than one of the GHC committees. MPTCs, GADTs (for example) have been in GHC far longer. OK it's bit naughty GHC doesn't have a flag for something that's not compliant to the report. But that's a GHC issue, not a grounds for changing the language spec. AntC > >> On 8 Sep 2017 8:35 am, "Anthony Clayden" wrote: >> ... _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-prime