ghci not loading function from file

Question

In test.hs, I have:

doubleMe x = x + x

In ghci, I type:

Prelude> :l test
[1 of 1] Compiling Main             ( test.hs, interpreted )
Ok, modules loaded: Main.
*Main> doubleMe 9

<interactive>:1:0: Not in scope: `doubleMe'
*Main> 

Why? How to fix?

Answer 1

Are you sure that you're loading the right test.hs? Maybe you're in the wrong directory. Or maybe you didn't save test.hs after adding the definition of doubleMe.

Answer 2

My guess is that you have defined a main function in your source file.

If you have defined a main function, loading the module with :l test won't import any functions but main. In that case you can load it by prepending an asterix to the module name: :l *test. The reason is that the compiled binary will hide non-exported top-level functions. Prepending an asterix forces GHCi to ignore the precompiled module (test) and interprete the source file instead (test.hs).

[jkramer/sgi5k:.../haskell]# cat test.hs 

main = do
    print $ doubleMe 2

doubleMe x = x + x

[jkramer/sgi5k:.../haskell]# ghc --make test
[jkramer/sgi5k:.../haskell]# ghci
[...some messages...]
>> :l test
Ok, modules loaded: Main.
>> :t doubleMe

<interactive>:1:0: Not in scope: `doubleMe'
>> :l *test
[1 of 1] Compiling Main             ( test.hs, interpreted )
Ok, modules loaded: Main.
>> :t doubleMe
doubleMe :: (Num a) => a -> a

Check these links for further information:

http://www.haskell.org/ghc/docs/6.12.2/html/users_guide/ghci-compiled.html http://www.haskell.org/ghc/docs/6.12.2/html/users_guide/interactive-evaluation.html#ghci-scope

Answer 3

1. Remove test.hi and test.o from the directory and then try ghci test. [Sometimes when I run ghc file.hs (and not ghc --make file.hs) it gives undefined reference error, but creates such files that are read by ghci later. Maybe this is a bug.]

2. Try

   :cd "<path to your file>"
   :l test
   :browse
   

   in ghci. What is the result?

Answer 4

This happened to me, too - and in case anyone else runs into it and stumbles across this page, my issue was that the VM I was running GHCI in was out of disk space - prompting it to try and load an empty file each time.