ghc-pkg: cannot find package ghc-7.10.2.20150906

Question

I need to expose a package ghc-7.10.2.20150906. When I use "ghc-pkg list", I see this:

But when I'm trying to expose ghc-7.10.2.20150906 by sudo ghc-pkg expose ghc-7.10.2.20150906, I get a message:

ghc-pkg: cannot find package ghc-7.10.2.20150906

What's the problem? Or is there another way to expose it?

Cabal file:

-- This is the configuration file for the 'cabal' command line tool.

-- The available configuration options are listed below.
-- Some of them have default values listed.

-- Lines (like this one) beginning with '--' are comments.
-- Be careful with spaces and indentation because they are
-- used to indicate layout for nested sections.


remote-repo: hackage.haskell.org:http://hackage.haskell.org/packages/archive
remote-repo-cache: /home/valoisa/.cabal/packages
-- local-repo:
-- logs-dir:
world-file: /home/valoisa/.cabal/world
-- verbose: 1
-- compiler: ghc
-- with-compiler:
-- with-hc-pkg:
-- scratchdir:
-- program-prefix: 
-- program-suffix: 
-- library-vanilla: True
-- library-profiling: False
-- shared:
-- executable-dynamic: False
-- executable-profiling: False
-- optimization: True
-- library-for-ghci: False
-- split-objs: False
-- executable-stripping: True
-- user-install: True
-- package-db:
-- flags:
-- extra-include-dirs:
-- extra-lib-dirs:
extra-prog-path: /home/valoisa/.cabal/bin
-- tests: False
-- library-coverage: False
-- benchmarks: False
-- cabal-lib-version:
-- constraint:
-- preference:
-- solver: choose
-- documentation: False
-- doc-index-file: $datadir/doc/index.html
-- max-backjumps: 2000
-- reorder-goals: False
-- shadow-installed-packages: False
-- strong-flags: False
-- reinstall: False
-- avoid-reinstalls: False
-- force-reinstalls: False
-- upgrade-dependencies: False
-- root-cmd:
-- symlink-bindir:
build-summary: /home/valoisa/.cabal/logs/build.log
-- build-log:
remote-build-reporting: anonymous
-- one-shot: False
jobs: $ncpus
-- username:
-- password:

install-dirs user
  -- prefix: /home/valoisa/.cabal
  -- bindir: $prefix/bin
  -- libdir: $prefix/lib
  -- libsubdir: $arch-$os-$compiler/$pkgid
  -- libexecdir: $prefix/libexec
  -- datadir: $prefix/share
  -- datasubdir: $arch-$os-$compiler/$pkgid
  -- docdir: $datadir/doc/$arch-$os-$compiler/$pkgid
  -- htmldir: $docdir/html
  -- haddockdir: $htmldir
  -- sysconfdir: $prefix/etc

install-dirs global
  -- prefix: /usr/local
  -- bindir: $prefix/bin
  -- libdir: $prefix/lib
  -- libsubdir: $arch-$os-$compiler/$pkgid
  -- libexecdir: $prefix/libexec
  -- datadir: $prefix/share
  -- datasubdir: $arch-$os-$compiler/$pkgid
  -- docdir: $datadir/doc/$arch-$os-$compiler/$pkgid
  -- htmldir: $docdir/html
  -- haddockdir: $htmldir
  -- sysconfdir: $prefix/etc

program-locations 
  -- alex-location:
  -- ar-location:
  -- c2hs-location:
  -- cpphs-location:
  -- ffihugs-location:
  -- gcc-location:
  -- ghc-location:
  -- ghc-pkg-location:
  -- greencard-location:
  -- haddock-location:
  -- happy-location:
  -- hmake-location:
  -- hpc-location:
  -- hsc2hs-location:
  -- hscolour-location:
  -- hugs-location:
  -- jhc-location:
  -- ld-location:
  -- lhc-location:
  -- lhc-pkg-location:
  -- nhc98-location:
  -- pkg-config-location:
  -- ranlib-location:
  -- strip-location:
  -- tar-location:
  -- uhc-location:

program-default-options 
  -- alex-options:
  -- ar-options:
  -- c2hs-options:
  -- cpphs-options:
  -- ffihugs-options:
  -- gcc-options:
  -- ghc-options:
  -- ghc-pkg-options:
  -- greencard-options:
  -- haddock-options:
  -- happy-options:
  -- hmake-options:
  -- hpc-options:
  -- hsc2hs-options:
  -- hscolour-options:
  -- hugs-options:
  -- jhc-options:
  -- ld-options:
  -- lhc-options:
  -- lhc-pkg-options:
  -- nhc98-options:
  -- pkg-config-options:
  -- ranlib-options:
  -- strip-options:
  -- tar-options:
  -- uhc-options:

Please post the command you used to compile and any output from that command. Are you using cabal? If so, please post the cabal file. If you're not using cabal you probably should be. — GarethR
@GarethR Thanks for your response, I've posted a cabal file. — O.Phillips

adamse adamse · Accepted Answer · 2015-11-25T10:31:32

Usually when you're writing a larger Haskell project you would specify the packages that you want to use in a project specific Cabal file, here is a quite minimal example that uses the base package and the ghc package, example.cabal:

name:                example
version:             0.1.0.0
build-type:          Simple
cabal-version:       >=1.10

library
  exposed-modules:     AModule
  build-depends:       base >= 4.7 && < 5
                       , ghc
  default-language:    Haskell2010

To use the GHC 7.10.3 snapshot with this project you run cabal configure --with-compiler=PATH/TO/ghc-7.10.3, then you can access your project with the dependent packages in a GHCi session using cabal repl.

If you really want to expose the ghc package your problem seems to be that the sudo ghc-pkg invocation is not the ghc-pkg from the 7.10.3 snapshot, as evidenced by the line

flag db stack: ["/home/valoisa/.ghc/x86_64-linux-7.10.2/package.conf.d","/usr/local/lib/ghc-7.10.2/package.conf.d"]

in the output of sudo ghc-pkg -v2 expose ghc you posted.

I can see two possible solutions

Don't use sudo as it seems the correct version of ghc-pkg is used (I can't think of any reason to use sudo here).
Use the correct ghc-pkg by specifying the whole path to the program.

ghc-pkg: cannot find package ghc-7.10.2.20150906

1 Answers