cabal error when building a simple tutorial project

Question

1 The Problem

I am following the tutorial How to Write a Haskell Program, in which you build the project haq.

Whenever I try to run cabal test, I get the following error snippet:

<command line>: cannot satisfy -package-id haq-0.1.0.0-inplace
    (use -v for more information)
    cabal: Error: some packages failed to install:
    haq-0.1.0.0 failed during the building phase. The exception was:
    ExitFailure 1

Notice that the package it cannot build is itself (at least I think that's what this error means).

2 The Details

2.1 The Full Error

$ cabal install --enable-tests
Resolving dependencies...
Configuring haq-0.1.0.0...
Building haq-0.1.0.0...
Failed to install haq-0.1.0.0
Build log ( /home/user/.cabal/logs/haq-0.1.0.0.log ):
Configuring haq-0.1.0.0...
Warning: The 'license-file' field refers to the file 'LICENSE' which does not
exist.
Building haq-0.1.0.0...
Preprocessing executable 'haq' for haq-0.1.0.0...
[1 of 1] Compiling Main             ( Haq.hs, dist/build/haq/haq-tmp/Main.o )
Linking dist/build/haq/haq ...
Preprocessing test suite 'tests' for haq-0.1.0.0...
<command line>: cannot satisfy -package-id haq-0.1.0.0-inplace
    (use -v for more information)
    cabal: Error: some packages failed to install:
    haq-0.1.0.0 failed during the building phase. The exception was:
    ExitFailure 1

2.2 Project File Structure

.
├── .cabal-sandbox
├── cabal.sandbox.config
├── dist
├── haq.cabal
├── Haq.hs
├── HSpecTests.hs
└── Setup.hs

2.3 Haq.hs

    --
    -- Copyright (c) 2006 Don Stewart - http://www.cse.unsw.edu.au/~dons/
    -- GPL version 2 or later (see http://www.gnu.org/copyleft/gpl.html)
    --
    import System.Environment

    -- | 'main' runs the main program
    main :: IO ()
    main = getArgs >>= print . haqify . head

    haqify s = "Haq! " ++ s

2.4 haq.cabal

    -- Initial haq.cabal generated by cabal init.  For further documentation, 
    -- see http://haskell.org/cabal/users-guide/

    name:                haq
    version:             0.1.0.0
    -- synopsis:            
    -- description:         
    -- license:             
    license-file:        LICENSE
    author:              First Last
    maintainer:          [email protected]
    -- copyright:           
    -- category:            
    build-type:          Simple
    -- extra-source-files:  
    cabal-version:       >=1.10

    executable haq
        main-is:             Haq.hs
        -- other-modules:       
        -- other-extensions:    
        build-depends:       base >=4.8 && <4.9
        -- hs-source-dirs:      
        default-language:    Haskell2010

    test-suite tests
        ghc-options: -Wall
        default-extensions:  OverloadedStrings
        type: exitcode-stdio-1.0
        main-is: HSpecTests.hs
        build-depends:       base,
                                                 haq,
                                                 hspec                >= 1.8
        default-language:    Haskell2010

2.5 HSpecTests.hs

    module Main where

    import Haq
    import Test.Hspec

    main :: IO ()
    main = hspec $ do

        describe "Validate haqify function" $ do
            it "haqify is supposed to prefix Haq! to things" $ do
                haqify "me" `shouldBe` "Haq! me"

ErikR · Accepted Answer · 2016-05-10 21:31:17Z

3

Update:

You get the error when you run cabal test.

The problem is that your test suite depends on the library haq, but the cabal file does not declare a library component. It only declares an executable.

To fix:

Rename the existing file Haq.hs to App.hs. Update the cabal file appropriately.

Create a new file 'Haq.hs` with this contents:

module Haq (haqify) where

haqify :: String -> String
haqify s = "Haqify! " ++ s

Add this stanza to the cabal file:

library
  build-depends: base >= 4.8 && < 4.9
  exposed-modules: Haq

Run cabal build or cabal test

Original Answer

I was able to cabal build your project once I fixed the indentation problems in Haq.hs:

removed the leading space on the lines for main
removed the leading space in front of haqify

edited May 10, 2016 at 21:31

answered May 10, 2016 at 21:18

ErikR

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4 Comments

George Over a year ago

I'm not sure how those leading spaces got up there, but they aren't present in my system (I'm adjusting the post now). Nevertheless, are you able to cabal install --enable-tests without error?

George Over a year ago

When I run cabal build, I still get the original error as well.

George Over a year ago

Also: my project builds fine with cabal install. It is only when I try to run the tests that I get this error.

ErikR Over a year ago

I don't think cabal install builds or runs any tests.

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cabal error when building a simple tutorial project

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2.2 Project File Structure

2.3 Haq.hs

2.4 haq.cabal

2.5 HSpecTests.hs

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