[Haskell-cafe] Re: what does the hidden package error mean?

Anatoly Yakovenko wrote:

On Fri, Apr 10, 2009 at 1:36 PM, Anatoly Yakovenko wrote:

...

I am trying to build ParseP on the latest ghc, and i am getting this error:

Text/ParserCombinators/ParseP/Interface.hs:26:17: __ __Could not find module `Data.ByteString.Char8': __ __ __it is a member of package bytestring-0.9.1.4, which is hidden

what does "hidden" mean? __why does this work in ghci

...

import Data.ByteString import Data.ByteString.Char8

without any problems

Ah, bytestring was missing from the build-depends,

what a confusing error message, can we change it to say

"package Foo is missing from the MyPackage.cabal build-depends"

would be a lot more obvious how to fix it.

The problem is that ghc doesn't know that, and shouldn't[1]: All it sees is a -hide-all-packages on its command line, you can witness it by calling cabal with the -v flag. OTOH, having some cross-compiler, machine-readable format to describe errors would enable cabal to do some holding of hands, as well as save ide developers from having to write all these boring parsers. [1] For UNIX fundamentalists, like me, MUST NOT -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.