I've opened Trac #11376 for this: https://ghc.haskell.org/trac/ghc/ticket/11376
Ryan S. On Thu, Jan 7, 2016 at 5:32 PM, Simon Peyton Jones <[email protected]> wrote: > Make a ticket? This would be worth capturing. > > I'm sure Richard will want to look at it when he gets back, and a ticket is a > useful workflow organiser. > > Simon > > | -----Original Message----- > | From: ghc-devs [mailto:[email protected]] On Behalf Of Ryan Scott > | Sent: 07 January 2016 17:55 > | To: GHC developers <[email protected]> > | Subject: Confused about specified type variables using -XTypeApplications > | > | I read in the Visible Type Applications paper [1] that you can only > | apply types to "specified" type variables. However, after trying out > | -XTypeApplications, I'm confused as to what exactly that means: > | > | $ /opt/ghc/head/bin/ghci > | GHCi, version 8.1.20160106: > | > https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fwww.haskell.o > | > rg%2fghc%2f&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7caa1fba8c2743424 > | > c1fb008d3178bb622%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=2B1fES1XwoQb8T > | MRj7oOkfdfoGo37oXhjnHFeqgOXAI%3d :? for help > | λ> :set -XTypeInType -XTypeApplications > | λ> data Prox a = Prox > | λ> let prox :: Prox a; prox = Prox > | λ> :t prox @Int > | prox @Int :: Prox Int > | λ> :t Prox @Int > | Prox @Int :: Prox a > | > | Huh? For some reason, I'm getting different types for prox @Int and > | Prox @Int! I think what's happening here is that in Prox @Int, the Int > | is being applied to a kind variable. That is, it's being applied to > | the k variable in: > | > | Prox :: forall k (t :: k). Prox t > | > | But why is this? After all, I don't think I "specified" k anywhere in > | the definition of Prox, and to make things more confusing, Int gets > | applied differently in prox @Int (and the definition of prox also > | doesn't mention k). Is this a bug, or am I misunderstanding something > | about -XTypeApplications? > | > | Ryan S. > | ----- > | [1] > | > https://na01.safelinks.protection.outlook.com/?url=http:%2f%2fwww.cis.upenn.e > | du%2f~eir%2fpapers%2f2016%2ftype-app%2fvisible-type- > | > app.pdf&data=01%7C01%7Csimonpj%40064d.mgd.microsoft.com%7Caa1fba8c2743424c1fb > | > 008d3178bb622%7C72f988bf86f141af91ab2d7cd011db47%7C1&sdata=PKUXsuMdixF76cVq0y > | yaCW8NZbIO5hOJpXwABfUkYZw%3d > | _______________________________________________ > | ghc-devs mailing list > | [email protected] > | > https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fmail.haskell. > | org%2fcgi-bin%2fmailman%2flistinfo%2fghc- > | > devs%0a&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7caa1fba8c2743424c1fb > | > 008d3178bb622%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=hV%2f3yHwiH36Qgegu > | hepSlx7JaZP0evwpGTTdK%2f3I3Po%3d _______________________________________________ ghc-devs mailing list [email protected] http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
