haskellghciunordered-containers

haskell, error ':set -package unordered-containers', ghci

I am just starting out with haskell.. trying out use of key value pairs..

came across this example on reddit

https://www.reddit.com/r/haskellquestions/comments/2xn9y2/whats_the_equivalent_of_a_python_dictionary_in/

λ> import qualified Data.HashMap.Strict as M
λ> let d = M.fromList [("a", 10.33), ("c", 20.23), ("d", 100.33)]
λ> d
fromList [("d",100.33),("a",10.33),("c",20.23)]
λ> M.lookup "c" d
Just 20.23
λ> M.insert "z" 77 d
fromList [("z",77.0),("d",100.33),("a",10.33),("c",20.23)]

when i try to run this it gives an error ':set -package unordered-containers'

When i do that the code runs..

What i am not clear is the following

  1. what does it mean?

  2. is that setting default? if not should i make it default?

  3. Lastly if i repeat the example in a haskell script what do i need to do to get the same setting?

I searched on google and found that it is a part of this package https://hackage.haskell.org/package/unordered-containers-0.2.19.1/docs/Data-HashMap-Strict.html

When i create a new project using stack and add dependency as

and run it it gives this error

/Users/air/haskell/thinkingFunctionally/myproj/src/Lib.hs:4:1: error:
    Could not find module ‘Data.HashMap.Strict’
    Perhaps you meant
      Data.Map.Strict (needs flag -package-id containers-0.6.7)
      Data.IntMap.Strict (needs flag -package-id containers-0.6.7)
    Use -v (or `:set -v` in ghci) to see a list of the files searched for.
  |
4 | import qualified Data.HashMap.Strict as M
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Error: [S-7282]
       Stack failed to execute the build plan.

       While executing the build plan, Stack encountered the error:

       [S-7011]
       While building package myproj-0.1.0.0 (scroll up to its section to see the error) using:
       /Users/air/.stack/setup-exe-cache/x86_64-osx/Cabal-simple_6HauvNHV_3.10.1.0_ghc-9.6.3 --verbose=1 --builddir=.stack-work/dist/x86_64-osx/ghc-9.6.3 build lib:myproj exe:myproj-exe --ghc-options " -fdiagnostics-color=always"
       Process exited with code: ExitFailure 1

my .cabal file is as under


source-repository head
  type: git
  location: https://github.com/githubuser/myproj

library
  exposed-modules:
      Lib
  other-modules:
      Paths_myproj
  autogen-modules:
      Paths_myproj
  hs-source-dirs:
      src
  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints
  build-depends:
      base >=4.7 && <5
  default-language: Haskell2010

executable myproj-exe
  main-is: Main.hs
  other-modules:
      Paths_myproj
  autogen-modules:
      Paths_myproj
  hs-source-dirs:
      app
  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -threaded -rtsopts -with-rtsopts=-N
  build-depends:
      base >=4.7 && <5
    , myproj
  default-language: Haskell2010

test-suite myproj-test
  type: exitcode-stdio-1.0
  main-is: Spec.hs
  other-modules:
      Paths_myproj
  autogen-modules:
      Paths_myproj
  hs-source-dirs:
      test
  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -threaded -rtsopts -with-rtsopts=-N
  build-depends:
      base >=4.7 && <5
    , myproj
  default-language: Haskell2010

This is my first post .. so i hope i am making sense here

thanks in advance for helping out..

Edit: Tried the same thing using cabal.. for anyone who has the same issue my new cabal file looks like this

executable myproject
    main-is:          Main.hs

    -- Modules included in this executable, other than Main.
    -- other-modules::

    -- LANGUAGE extensions used by modules in this package.
    -- other-extensions:
    build-depends:    base ^>=4.15.1.0
                     ,unordered-containers >=0.2.19.1 
                      
    hs-source-dirs:   app
    default-language: Haskell2010
Solution

  • Add the unordered-comtainers to the build-depedends:

    library
  # …
  build-depends:
      base >=4.7 && <5
      unordered-containers >=0.2.19.1