Haskell Stack: installed packages are not visible

Question

I installed package with stack install but I cannot import the package unless I use stack ghc or stack ghci ...

The problem is I have installed atom haskell ide, that uses ghc-mod backend, which also doesn't see packages installed by stack!

Answer 1

You'll want to ensure that you have a ghc-mod that is both recent and built by the same version of ghc as the one your project is using. Do this by installing with stack (using the same resolver as your project). e.g.

$ stack install --resolver lts-6.11 ghc-mod
$ which ghc-mod
/Users/steshaw/.local/bin/ghc-mod
$ ghc-mod --version
ghc-mod version 5.5.0.0 compiled by GHC 7.10.3

To test this, perhaps set up an example project with stack new.

$ stack new example
$ cd example

Change example.cabal to include, say, the HTTP package for the example-exe.

e.g.

executable example-exe
  hs-source-dirs:      app
  main-is:             Main.hs
  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
  build-depends:       base
                     , example
                     , HTTP
  default-language:    Haskell2010

Build with stack to install the HTTP package.

$ stack build

Now start Atom.

$ atom .

You should find that the imports from HTTP are visible within Atom.