#12126: Bad error messages for SPECIALIZE pragmas -------------------------------------+------------------------------------- Reporter: antalsz | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Specialize, | ErrorMessages, newcomer Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by mpickering): Thanks, this is a good bug report and something good for a newcomer to get started with. I think that fixing at least (2) and (3) should be easy. Here are my investigations so far: 1. Specialisation signatures are handled in `TcBinds.tcSpecPrags`. 2. `unifyType` fails to solve `Bool ~ (Num a => a -> a)` so it gets deferred to later on in the constraint solving process. At which point it is defaulted for some reason. 1. The outer error context is added in `tcSpecPrag`. 2. The inner error context is added as a result of `hsSigDoc`. Suggestion: Modify the outer context added in `tcSpecPrag`. 1. The actual text that a user used can be found in the `inl_src` field of the `InlinePragma` field of `SpecSig`. Suggestion: There should be a few places to change where you can use this value rather than hard-coding `SPECIALISE`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12126#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler