#15379: Don't reject user-written instances of KnownNat and friends in hsig files -------------------------------------+------------------------------------- Reporter: ezyang | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Resolution: | Keywords: backpack Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): I'm not sure I'm following all the details here, but can you take inspiration from the way that instances in `hs-boot` files work? If you have {{{ Foo.hs-boot data T instance Eq T }}} then in the `hi-boot` file (which we get from compiling `Foo.hs-boot`) we will have something like {{{ $d77 : Eq T }}} That is, the arbtrarily named `$d77` is a witness for `Eq T`. Modules importing `Foo.hi-boot` use `$d77` when they need `Eq T`. Then when compiling `Foo.hs` we generate the real instance {{{ $d98 = <the code for equality on T> :: Eq T }}} and (having read the `Foo.hi-boot` file, we also generate a compatibility stub {{{ $d77= $d98 }}} so that references to `$d77` will end up in `$d98`. Maybe the same approach will work for `hsig` files. Edward will know. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15379#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler