No instance for (Show Builder) in bytestring-0.10.4.0

[jkozlowski]

Compiling against bytestring-0.10.4.0 (which happened to be released when I checked out code and tried to build) is missing Show instance for http://hackage.haskell.org/package/bytestring-0.10.4.0/docs/Data-ByteString-Builder.html.

I am thinking of trying this http://www.haskell.org/cabal/users-guide/developing-packages.html#conditional-compilation over the weekend to fix the build (effectively add conditional compilation). Unless you think that's an overkill?

[NicolasT]

Where does this fail?

[jkozlowski]

Sorry I meant to copy this in, and then I forgot:

src/Network/Kontiki/Types.hs:342:13:
    No instance for (Show Builder)
      arising from the 'deriving' clause of a data type declaration
    Possible fix:
      add an instance declaration for (Show Builder)
      or use a standalone 'deriving instance' declaration,
           so you can specify the instance context yourself
    When deriving the instance for (Show (Command a))

[NicolasT]

Hmm... I guess it makes some sense Builder no longer Has a Show instance, but I'd dislike no longer having a Show instance for Command, mainly for debugging/tracing purposes, which is (I suppose) what you propose?

I'd say a hand-written instance with the CLog value expanded in the result would be more useful?

[jkozlowski]

I agree about the debugging and no Show instance...

I just added the following to silence the compiler:

import Data.ByteString.Builder (toLazyByteString)

instance Show Builder
  where show = show . toLazyByteString

[NicolasT]

That'd introduce an orphan instanc. We really shouldn't have those in any of the Kontiki library modules!

[jkozlowski]

Ouch, gotcha. Still learning

[NicolasT]

No worries :smiley: Not sure how to work around though (except writing tedious instances by hand...)