Leksah default hello world is not working after installation Xubuntu 13.10

Question

I've installed Leksah 0.12.1.3 on Xubuntu 13.10 from terminal.

sudo apt-get install leksah

Opened leksah, created new workspace and package. Main.hs is created by default with 'Hello world' program.

module Main (
    main
) where

import Control.Monad (unless)
import Data.List (stripPrefix)
import System.Exit (exitFailure)
import Test.QuickCheck.All (quickCheckAll)

-- Simple function to create a hello message.
hello s = "Hello " ++ s

-- Tell QuickCheck that if you strip "Hello " from the start of
-- hello s you will be left with s (for any s).
prop_hello s = stripPrefix "Hello " (hello s) == Just s

-- Hello World
exeMain = do
    putStrLn (hello "World")   

-- Entry point for unit tests.
testMain = do
    allPass <- $quickCheckAll -- Run QuickCheck on all prop_ functions
    unless allPass exitFailure

-- This is a clunky, but portable, way to use the same Main module file
-- for both an application and for unit tests.
-- MAIN_FUNCTION is preprocessor macro set to exeMain or testMain.
-- That way we can use the same file for both an application and for tests.
#ifndef MAIN_FUNCTION
#define MAIN_FUNCTION exeMain
#endif
main = MAIN_FUNCTION

Now, if I try to run package, or write anything in editor, in lower-right window
========== 127 ==========================
appears.

Answer 1

This happens to me a lot.... I don't know what the cause is, but (at least in my case) I know I can fix the problem by just using the command line. I just "cd" into the directory with the package (the one with the *.cabal file), and type

cabal configure
cabal build

after this is done, Leksah works properly. Clearly it is a Leksah bug, but it is easy to work around.

Answer 2

Problem was in my naive assumption that 'apt-get install leksah' will install all needed packages. However, that's not correct.

After leksah installation you'll need:

apt-get install cabal-install
apt-get install ghc
cabal update

After that, as jamshidh mentioned, you need to click package->cofigure.

Now build brakes with (for program posted in question, which is leksah autogenerated default):

Couldn't match type `IO' with `[]'
Expected type: String
  Actual type: IO ()
In the first argument of `putStrLn', namely `testMain'
In the expression: putStrLn testMain
In an equation for `main': main = putStrLn testMain

But I managed to build much simpler version:

module Main (
  main
) where
main = putStrLn "Hello World"

Answer 3

The problem with the default hello world is the following line:

putStrLn (hello "World")   

It's simply that the left quote is not in the correct place. Change that to

putStrLn ("hello World")   

and it should work.