#12989: ($) can have a more general type -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Keywords: Resolution: | LevityPolymorphism Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * keywords: => LevityPolymorphism Comment: Worth reading our [https://www.microsoft.com/en-us/research/publication /levity-polymorphism/ levity polymorphism paper]. `good` is OK because no value of type `a` is manipulated by the code for `good` (see the paper). NB: care is needed during optimisation: eta expansion (to get `bad`) is not allowed. So, yes, perhaps `($)` could be defied like `good`, as an arity-1 function. Then it could have the more generous type. I'll add this to the levity-polymorphism pile; see [wiki:LevityPolymorphism] -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12989#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler