I am working on the "roman-numerals" task from the exercism Haskell track and followed their instructions to installing stack. I am working on a Fedora 24 box.
As long as I was working with Haskell modules from base, I didn't have a problem. Now I am trying to import the Data.Map module. It works fine using the ghci command line:
$ ghci
GHCi, version 7.8.4: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> import Data.Map
Prelude Data.Map>
However, when I try to import it from inside my src file with the command:
import qualified Data.Map as M (foldlWithKey, fromList)
I am running into problems when I try to run the test:
$ stack test
roman-numerals-0.0.0: build (lib + test)
Preprocessing library roman-numerals-0.0.0...
[2 of 2] Compiling Roman (...)
(...) /roman-numerals/src/Roman.hs:3:1: error:
Failed to load interface for ‘Data.Map’
It is a member of the hidden package ‘containers-0.5.7.1’.
Perhaps you need to add ‘containers’ to the build-depends in your .cabal file.
Use -v to see a list of the files searched for.
Progress: 1/2
(...)
I googled the problem and found a straightforward solution at the Cabal FAQ at haskell.org:
What you need to do is to add containers to the build-depends in your .cabal file.
I am assuming they mean the file roman-numerals.cabal that is in my working directory. The contents are:
-- This file has been generated from package.yaml by hpack version 0.14.0.
--
-- see: https://github.com/sol/hpack
name: roman-numerals
version: 0.0.0
build-type: Simple
cabal-version: >= 1.10
library
hs-source-dirs:
src
build-depends:
base
exposed-modules:
Roman
other-modules:
Paths_roman_numerals
default-language: Haskell2010
test-suite test
type: exitcode-stdio-1.0
main-is: Tests.hs
hs-source-dirs:
test
build-depends:
base
, roman-numerals
, hspec
default-language: Haskell2010
I tried to add "containers" to the build-depends in either and both the "library" and "test-suite" sections, but when I run
$ stack test
the error persists, and the .cabal file is reverted to the same contents shown above.
Any pointers? Much appreciated!