#10516: PolyKinds results in incorrect reporting of type synonym parameter count -------------------------------------+------------------------------------- Reporter: benjamin.hodgson | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: MacOS X | Architecture: x86_64 Type of failure: None/Unknown | (amd64) Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Description changed by benjamin.hodgson: Old description:

The following program is invalid because the declaration of `f` doesn't fully apply `App` to all of its arguments.

{{{#!hs {-# LANGUAGE PolyKinds #-}

type App f a = f a

newtype X f a = X (f a)

f :: f a -> X (App f) a f = X }}}

However, with the `PolyKinds` extension, the error reporting is quite weird:

{{{ Type synonym ‘App’ should have 4 arguments, but has been given 3 In the type signature for ‘f’: f :: f a -> X (App f) a }}}

`App` has ''two'' arguments, and I gave it ''one''! I'm guessing that `PolyKinds` makes GHC supply some implicit parameters during expansion of type synonyms, and that's what gets reported in the error message. The behaviour is correct without `PolyKinds`.

I've tested this on GHC 7.8.3 (the Haskell Platform version).

New description: The following program is invalid because the declaration of `f` doesn't fully apply `App` to all of its arguments. {{{#!hs {-# LANGUAGE PolyKinds #-} type App f a = f a newtype X f a = X (f a) f :: f a -> X (App f) a f = X }}} However, with the `PolyKinds` extension, the error reporting is quite weird: {{{ Type synonym ‘App’ should have 4 arguments, but has been given 3 In the type signature for ‘f’: f :: f a -> X (App f) a }}} `App` has ''two'' arguments, and I gave it ''one''! I'm guessing that `PolyKinds` makes GHC supply some implicit parameters during expansion of type synonyms, and that's what gets reported in the error message. The behaviour is correct without `PolyKinds`. I've tested this on GHC 7.8.3 (the Haskell Platform version) on my 64-bit OSX Yosemite system. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10516#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10516: PolyKinds results in incorrect reporting of type synonym parameter count -------------------------------------+------------------------------------- Reporter: benjamin.hodgson | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: MacOS X | Architecture: x86_64 Type of failure: None/Unknown | (amd64) Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by goldfire): * version: 7.8.3 => 7.10.1 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10516#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10516: PolyKinds results in incorrect reporting of type synonym parameter count -------------------------------------+------------------------------------- Reporter: benjamin.hodgson | Owner: Type: bug | Status: merge Priority: high | Milestone: 7.10.3 Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: MacOS X | Architecture: x86_64 Type of failure: None/Unknown | (amd64) Blocked By: | Test Case: Related Tickets: | polykinds/T10516 | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by simonpj): * priority: normal => high * status: new => merge * testcase: => polykinds/T10516 * milestone: => 7.10.3 Comment: I believe I have fixed this. Could merge to the branch if convenient. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10516#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler