Question

I write the following file temp.hs:

import qualified Data.Set
import System.Environment

main :: IO ()
main = do
        args <- getArgs
        let fname = head args
        print (fname)

It loads in ghci without errors:

$ ghci
GHCi, version 6.12.3: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
Prelude> :load temp.hs 
[1 of 1] Compiling Main             ( temp.hs, interpreted )
Ok, modules loaded: Main.
*Main> 

When I try to compile it, I get the following errors:

$ ghc temp.hs -o temp
Undefined symbols:
  "___stginit_containerszm0zi3zi0zi0_DataziSet_", referenced from:
      ___stginit_Main_ in temp.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

If I take the import Data.Set out, it compiles fine.

Version Info:

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.12.3

$ gcc --ver
Using built-in specs.
Target: i686-apple-darwin10
Configured with: /var/tmp/gcc_40/gcc_40-5494~112/src/configure --disable-checking -enable-werror --prefix=/usr --mandir=/share/man --enable-languages=c,objc,c++,obj-c++ --program-transform-name=/^[cg][^.-]*$/s/$/-4.0/ --with-gxx-include-dir=/include/c++/4.0.0 --with-slibdir=/usr/lib --build=i686-apple-darwin10 --with-arch=apple --with-tune=generic --host=i686-apple-darwin10 --target=i686-apple-darwin10
Thread model: posix
gcc version 4.0.1 (Apple Inc. build 5494)

Answer 1

You can add packages individually (as KennyTM suggests), or you can just use --make, which is much more convenient in a number of ways:

ghc --make temp.hs -o temp

This will cause GHC to look for any required modules among its installed packages in exactly the same way that GHCi does.