#16059: checkValidType is defeated by a type synonym -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.10.1 Component: Compiler (Type | Version: 8.7 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC accepts | Unknown/Multiple invalid program | Test Case: Blocked By: | Blocking: 16140 Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): It turns out that option (1) from comment:4 is just plain infeasible. If you implement it, then several test cases that should fail suddenly pass. `tcfail129` is one example: {{{#!hs module ShouldFail where data T = T -- This was erroneously accepted type Foo a = String -> Maybe a type Bar m = m Int blah = undefined :: Bar Foo type Foo1 a = Maybe a type Bar1 m = m Int blah1 = undefined :: Bar1 Foo1 }}} This should fail due to the unsaturated use of `Foo`/`Foo1`, but if we always expand, then we'll never catch that! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16059#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler