| And I am wondering if there is a way for GHC to discriminate between | these two options somehow… Not that I know of. Simon | -----Original Message----- | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Joachim | Breitner | Sent: 20 May 2017 18:14 | To: ghc-devs@haskell.org | Subject: Re: How lose can we be with strictness | | Hi, | | yes, of course. What GHC is doing now is correct, safe and what an | (exprienced) programmer expects. Especially if he is using `x==x` to | deeply force x… | | But then I presume that there are many uses of code like this where the | effect of `==` forcing its arguments is a necessary side effect of | deciding the equality, and if the compiler finds a different way of | deciding the equality, e.g. statically, the programmer would be happy to | have `n` as dead code, with all the advantages this provides. | | And I am wondering if there is a way for GHC to discriminate between | these two options somehow… | | Joachim | | | Am Samstag, den 20.05.2017, 12:07 -0500 schrieb Christopher Allen: | > Correct me if I'm wrong here, but it's preserving the effect of (==) | > forcing its arguments. This makes the optimization less surprising, in | > my opinion. | > | > Is there a benefit to not doing this? | > | > On Sat, May 20, 2017 at 11:56 AM, Joachim Breitner | > wrote: | > > Hi, | > > | > > I just observed that GHC optimizes | > > | > > fun (n::Int) = n == 0 + n | > > | > > to essentially | > > | > > fun (n::Int) = n `seq` True | > > | > > | > > I am wondering under what circumstances we would be happy to | > > transform this further to | > > | > > fun _ = True | > > | > > | > > Clearly, we do not want to drop `seq`s in general. But is there some | > > commonly accepted rule about which strictness we generally allow the | > > compiler to get rid of, if it turns out that the compiler can do | > > without? Or are all such transformations out of bounds for GHC? | > > | > > Greetings, | > > Joachim | > > | > > -- | > > Joachim Breitner | > >   mail@joachim-breitner.de | > > | > > https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww. | > > joachim-breitner.de%2F&data=02%7C01%7Csimonpj%40microsoft.com%7C4840 | > > 85dababa49deee5c08d49fa3a18a%7C72f988bf86f141af91ab2d7cd011db47%7C1% | > > 7C0%7C636308972543295456&sdata=mCYy2wGpdTvnCofPEBiVsYfRggxxUd9m3SPEu | > > fTQAJg%3D&reserved=0 | > > | > > _______________________________________________ | > > ghc-devs mailing list | > > ghc-devs@haskell.org | > > https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmail | > > .haskell.org%2Fcgi-bin%2Fmailman%2Flistinfo%2Fghc-devs&data=02%7C01% | > > 7Csimonpj%40microsoft.com%7C484085dababa49deee5c08d49fa3a18a%7C72f98 | > > 8bf86f141af91ab2d7cd011db47%7C1%7C0%7C636308972543295456&sdata=XdESs | > > wIFC2EByMcyYyhVcq40Q0SPEujNKgY8Oqv%2Ff3Q%3D&reserved=0 | > > | > | > | > | -- | Joachim Breitner | mail@joachim-breitner.de | | https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.joach | im- | breitner.de%2F&data=02%7C01%7Csimonpj%40microsoft.com%7C484085dababa49dee | e5c08d49fa3a18a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636308972543 | 295456&sdata=mCYy2wGpdTvnCofPEBiVsYfRggxxUd9m3SPEufTQAJg%3D&reserved=0