#11376: Inconsistent specified type variables among functions and datatypes/classes when using -XTypeApplications -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.1 checker) | Keywords: Resolution: | TypeApplications Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I found another inconsistency with regards to datatypes vs. data families and visible type application. Let's define a datatype first: {{{ $ /opt/ghc/head/bin/ghci GHCi, version 8.1.20160120: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/xnux/.ghci λ> :set -XTypeInType -XTypeApplications λ> data T k2 k4 (f :: k1 -> k2 -> k3 -> k4) = T λ> :t T T :: forall k1 k3 k2 k4 (f :: k1 -> k2 -> k3 -> k4). T k2 k4 f λ> :t T @Int T @Int :: forall k3 k2 k4 (f :: Int -> k2 -> k3 -> k4). T k2 k4 f }}} Nothing surprising here. The type variables are topologically sorted such that the last three variables correspond to the specified type variables. Looks good. But if I define the equivalent data family instance, I get a surprisingly different result: {{{ λ> :set -XTypeInType -XTypeApplications -XTypeFamilies λ> data family T (a :: k1) (b :: k2) (c :: k3) λ> data instance T k2 k4 (f :: k1 -> k2 -> k3 -> k4) = T λ> :t T T :: forall k2 k4 k1 k3 (f :: k1 -> k2 -> k3 -> k4). T k2 k4 f λ> :t T @Int T @Int :: forall k4 k1 k3 (f :: k1 -> Int -> k3 -> k4). T Int k4 f }}} This time, the kind variables are in a completely different order! The specified kind variables now come before the invisible kind variables, and as a result, `T @Int` has a completely different type. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11376#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler