[GHC] #11101: Expand Template Haskell type splices before quantification
#11101: Expand Template Haskell type splices before quantification -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider {{{ f :: Int -> $(foo) f = ... }}} This is a Template Haskell type splice. What if `$(foo)` expands to `a -> a`. Then it should all behave as if you'd written {{{ f :: Int -> a -> a f = ... }}} But it doesn't, because we collect the variables over which we will implicitly quantify ''before expanding splices''. This is made yet more tricky when we add type wildcards to the mix. And really there is no good reason for this trouble. We should simply expand the splice, and ''then'' decide what to quantify over. A little bit of refactoring in `RnTypes`. This ticket is just to record that I intend to do this shortly. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11101 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11101: Expand Template Haskell type splices before quantification -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by simonpj: Old description:
Consider {{{ f :: Int -> $(foo) f = ... }}} This is a Template Haskell type splice. What if `$(foo)` expands to `a -> a`. Then it should all behave as if you'd written {{{ f :: Int -> a -> a f = ... }}} But it doesn't, because we collect the variables over which we will implicitly quantify ''before expanding splices''.
This is made yet more tricky when we add type wildcards to the mix.
And really there is no good reason for this trouble. We should simply expand the splice, and ''then'' decide what to quantify over. A little bit of refactoring in `RnTypes`.
This ticket is just to record that I intend to do this shortly.
New description: Consider {{{ f :: Int -> $(foo) f = ... }}} This is a Template Haskell type splice. What if `$(foo)` expands to `a -> a`. Then it should all behave as if you'd written {{{ f :: Int -> a -> a f = ... }}} But it doesn't, because we collect the variables over which we will implicitly quantify ''before expanding splices''. This is made yet more tricky when we add type wildcards to the mix. And really there is no good reason for this trouble. We should simply expand the splice, and ''then'' decide what to quantify over. A little bit of refactoring in `RnTypes`. This ticket is just to record that I intend to do this shortly. It's possible that #11098 is related; I'm not sure. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11101#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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