Cabal: No 'Main-Is' field found for executable test1

Question

I am trying to run a very simple "Hello World" project with cabal.

This is the folder (ubuntu) where I have saved my project

mtt@mttPC:~/Documents/Haskell/test1$ ls
dist          Greetings.o  Setup.hs  test1.cabal

Main.hs contains:

module Greetings where

main :: IO ()
main = print "hello"

Hello world actually works:

mtt@mttPC:~/Documents/Haskell/test1$ runhaskell Main.hs configure --ghc
"hello"

The test1.cabal file has been generated with cabal init:

-- Initial test1.cabal generated by cabal init.  For further documentation,
--  see http://haskell.org/cabal/users-guide/

name:                test1
version:             0.1.0.0
-- synopsis:            
-- description:         
-- license:             
license-file:        LICENSE
author:              mtt
maintainer:           
-- copyright:           
-- category:            
build-type:          Simple
cabal-version:       >=1.8

executable test1
  -- main-is: Main.hs     
  -- other-modules:     
  build-depends:       base ==4.6.*

I don't understand why:

mtt@mttPC:~/Documents/Haskell/test1$ cabal configure
Resolving dependencies...
Configuring test1-0.1.0.0...

Error: No 'Main-Is' field found for executable test1

Answer 1

You forgot to uncomment the file that tells GHC what module to build as the main entry point

...
executable test1
  main-is: src/Main.hs -- Or whatever is appropriate
  build-depends: base==4.6.*