Hi Cafe, > > I've bumped into a strange error message -- it looks like an obvious > bug, but maybe there's something that I'm just not aware of: > GHCi, version 7.10.1: http://www.haskell.org/ghc/ :? for help > ghci> type Test a = a > ghci> type Huh = Test > > <interactive>:3:1: > Type synonym ‘Test’ should have 1 argument, but has been given none In the type declaration for ‘Huh’ > > So far, so good: > > ghci> :set -XPolyKinds > ghci> type Test a = a > ghci> type Huh = Test > > <interactive>:6:1: > Type synonym ‘Test’ should have 2 arguments, but has been given 1 > In the type declaration for ‘Huh’ > > (Notice
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 I would guess the two arguments are a kind and a type of that kind. The kind is given implicitly, so this corresponds to your one given argument. If we specify a kind, we get the following: Prelude> :set -XPolyKinds -XDataKinds -XKindSignatures Prelude> type Test a = a Prelude> type Huh a = Test (a :: Bool) Prelude> type Bar = Huh <interactive>:5:1: Type synonym ‘Huh’ should have 1 argument, but has been given none In the type declaration for ‘Bar’ So it really takes two arguments and we can specify one, leaving one to be specified. Maybe a better error message would be useful, but I would not say this is a bug. On 07/17/2015 08:37 PM, Nikolay Amiantov wrote: the number of arguments reported in the second case) > -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQEcBAEBCAAGBQJVqV0gAAoJEM0PYZBmfhoBEYYH/2dbUfsM9X9EKRaGdrsGmRlx Yj51KkvO8uGDfoFfu++JuCY/o0poD3/NQLUtHOrUx9tKrGD+Kksoqs5+3jKdKWhb x4SITIShOOd31qwwKdfs7QaTdrP1cyr/km9U5wP5o8Zgf9XCUI337RC6HRuhphcb Ytk+We3ZODy1+SewMjYvJvOiTfzTAa3u4zW1arEcXMXaaIcyMwtfH+UMgSljbBUt K9nfWE73klyftae3duSonML0fwTgUepnhRrZ+weIS0fEHqfJDsy4KJKqJGm2ee8T w72D69FNVvwkL46TH7rZKhHyh3k7Ct5SHb14IqyDDduobFtswfhCpGjdLXyfn3o= =5hgl -----END PGP SIGNATURE-----