Anyway, I think I figured it out:
Hint is using the Show instance of ErrMsg.
But it is defined only in term of errMsgShortString:
https://www.haskell.org/ghc/docs/7.6.3/html/libraries/ghc-7.6.3/src/ErrUtils...
So we are missing the context infos.
On Tue, Sep 9, 2014 at 12:01 AM, Corentin Dupont
Hi everybody, I am working with Hint, after some discussion with Daniel Gorin, I decided to post here, I hope it's the right place. My problem with Hint is that I cannot get context in error messages while interpreting a string. If you run the attached file example.hs, you get:
GhcError {errMsg = "No instance for (GHC.Num.Num GHC.Base.String)\n arising from a use of `GHC.Num.+'\nPossible fix:\n add an instance declaration for (GHC.Num.Num GHC.Base.String)"}
There is no context (line number, code snippets...), plus the error message uses fully qualified names, which is not very readable. It's very hard to figure out where the problem is when interpreting a long string. But the same error in a file that is loaded with Hint gives the correct message (uncomment the putStrLn in SomeModule.hs to get it):
GhcError {errMsg = "<no location info>:\n [1 of 1] Compiling SomeModule ( SomeModule.hs, interpreted )"},GhcError {errMsg = "SomeModule.hs:5:22:\n No instance for (Num String) arising from a use of `+'\n Possible fix: add an instance declaration for (Num String)\n In the second argument of `($)', namely `\"bar\" + 1'\n In a stmt of a 'do' block: putStrLn $ \"bar\" + 1\n In the expression:\n do { putStrLn \"bar\";\n putStrLn $ \"bar\" + 1 }"}
This error is much better: it gives line number plus some code snippets ("In the second argument of...").
There might be a flag that is not correctly set in GHC? After a quick look I'm thinking of GHC.DynFlags (I'm no expert). Now it is configured with: configureDynFlags :: GHC.DynFlags -> GHC.DynFlags configureDynFlags dflags = dflags{GHC.ghcMode = GHC.CompManager, GHC.hscTarget = GHC.HscInterpreted, GHC.ghcLink = GHC.LinkInMemory, GHC.verbosity = 0}
Thanks, Corentin