Producing multiple executables from single project

Question

With the following project structure:

src/FirstExecutable.hs src/SecondExecutable.hs my-amazing-project.cabal 

and the following cabal setup:

name:               my-amazing-project version:            0.1.0.0 build-type:         Simple cabal-version:      >=1.8  executable first-executable   hs-source-dirs:   src   main-is:          FirstExecutable.hs   ghc-options:      -O2 -threaded -with-rtsopts=-N   build-depends:    base == 4.5.*  executable second-executable   hs-source-dirs:   src   main-is:          SecondExecutable.hs   ghc-options:      -O2 -threaded -with-rtsopts=-N   build-depends:    base == 4.5.* 

Running cabal install fails with the following output:

Installing executable(s) in /Users/mojojojo/Library/Haskell/ghc-7.4.2/lib/my-amazing-project-0.1.0.0/bin cabal: dist/build/second-executable/second-executable: does not exist Failed to install my-amazing-project-0.1.0.0 cabal: Error: some packages failed to install: my-amazing-project-0.1.0.0 failed during the final install step. The exception was: ExitFailure 1 

What am I doing wrong or is this a Cabal bug?

---

The contents of the executable modules are as follows:

module FirstExecutable where  main = putStrLn "Running FirstExecutable" 

and

module SecondExecutable where  main = putStrLn "Running SecondExecutable" 

Answer 1

cabal expects the module of the executable to be Main. You should skip the module line or use module Main where.

Ok here is the possible reason. The executable of a haskell program is not produced when the module is not Main when you actually compile the program. The main function of the Main module is used when the executable is run. A possible workaround for ghc is -main-is flag. So you can have something like

name:               my-amazing-project version:            0.1.0.0 build-type:         Simple cabal-version:      >=1.8  executable first-executable   hs-source-dirs:   src   main-is:          FirstExecutable.hs   ghc-options:      -O2 -threaded -with-rtsopts=-N -main-is FirstExecutable   build-depends:    base == 4.5.*  executable second-executable   hs-source-dirs:   src   main-is:          SecondExecutable.hs   ghc-options:      -O2 -threaded -with-rtsopts=-N -main-is SecondExecutable   build-depends:    base == 4.5.*