On 2013-09-03 16:19, Simon Peyton-Jones wrote:
Some comments on the code.
Use warnTc or addWarnTc, rather than fiddling with mkPlainWarnMsg etc. Ditto in checkShouldInst, instead of returning a (Maybe WarnMsg), just use warnTc inside checkShouldInst.
Why not just getInstEnvs and lookupInstEnv in checkShouldInst, much as in TcInteract.matchClassInst? Instead you are passing parameters around that are readily available in the Tc monad.
Still getting used to the API, will refactor :-)
Don't use tryTc in tcLookupClassMaybe -- it's a sledgehammer to crack a nut. The only classes you are looking up are monad, applicative, alternative, and they will always be found -- or at least if not we have a problem, and tcLookupClass will rightly report an error. So I see no need for this tryTc and matching on maybes.
The use of tryTc there fixed the problem we (me and Dan) discussed recently on ghc-devs: the testsuite errors with GHC/Base.lhs:1:1: GHC internal error: ‛GHC.Base.Monad’ is not in scope during type checking, but it passed the renamer tcl_env of environment: [] (and the full build errored with "missing interfaces for GHC.Base"). The maybe business fixed this. (Subject of the discussion: "Cannot make ghc: Failed to load interface for GHC.Base") Also note that the Prelude is not necessarily imported, so I think the lookups here can fail regardless of the issue mentioned before.
I don't see any documentation.
In what sense? More comments, longer function headers? I thought the names used were clear, with comments giving an overview over longer sections. (If you're talking about Haddock: the AMP functions are not exported, hence no HTML docs. tcAmpWarn is called from inside tcTopSrcDecls in the same module.)
I don't know about this validation stuff; maybe others can help. Why not *not* add -fno-warn-amp to GcStage1HcOpts?
The flag is mysteriously passed to the existing GHC, i.e. it appears when building phase 1. However, the current compiler doesn't know about the flag and fails. (This was my initial attempt.) Thanks for the advice, David/quchen