Could not find module 'Data.Set'

Question

I have the following RPM packages installed on my Fedora 28 system:

ghc-ghc-8.2.2-66
ghc-containers-0.5.10.2-66

According to hackage the set module should be included in the given RPMs. However trying to import Data.Set results in

<no location info>: error:
    Could not find module ‘Data.Set’
    Perhaps you meant Data.Int (from base-4.10.1.0)

Did I miss something to install? How can I check which modules are available?

Edit:

$ ghc-pkg list
/usr/lib64/ghc-8.2.2/package.conf.d
    base-4.10.1.0
    ghc-prim-0.5.1.1
    integer-gmp-1.0.1.0
    rts-1.0

How do I register a module?

Answer 1

I would skip the operating system packages and go with stack:

$ wget -o get-stack.sh https://get.haskellstack.org/
$ chmod +x get-stack.sh
$ ./get-stack.sh -d ~/.local/bin
$ echo 'export PATH="~/.local/bin:$PATH"' >> ~/.bashrc
$ source ~/.bashrc
$ stack --version
Version 1.7.1, Git revision ...

Then use stack ghc to run GHC; the first time it will install this:

$ stack ghc
Writing implicit global project config file to: ...
Note: You can change the snapshot via the resolver field there.
Using latest snapshot resolver: lts-12.9
Downloaded lts-12.9 build plan.    
Preparing to install GHC to an isolated location.

Answer 2

For anyone new like me who finds this, you need to add containers to your package.yaml dependencies in order to import Data.Set. My package.yaml dependencies looked like this to get a Data.Set import to work:

dependencies:
  - base >= 4.7 && < 5
  - containers > 0.6

Then you can import Data.Set in your file like

import Data.Set (Set)
import qualified Data.Set as Set

Answer 3

ghc-containers contains only the shared library (.so) for compiled programs that are linked to it. If you wish to use the library in development, install ghc-containers-devel:

$ dnf install -y ghc-containers-devel
$ ghci
GHCi, version 8.2.2: http://www.haskell.org/ghc/  :? for help
Prelude> import Data.Set
Prelude Data.Set>