EclipseOn Mac OS X
However, getting syntax highlighting working requires a little work. The "scion-browser" and "buildwrapper" don't seem to install correctly, probably something to do with permissions. You will see errors whenever your try and let Eclipse install and build them, or just ignore the fact they are missing.
Even if you skip the work for getting syntax highlighting working, EclipseFp is currently (early 2012) the easiest tool to get working for reliable edit/compile on Mac OS X, so it is a good choice for beginners.
Build them from the command line with cabal, making sure everything is up to date.
cabal install zlib
cabal install scion-browser
cabal install buildwrapper
The executables you need will likely be in a hidden directory "Library/Haskell/bin" of your home directory. i.e. if your user id is "foo" then the path will be "/Users/foo/Library/Haskell/bin". That folder may not show in finder or spotlight.
In Eclipse, select preferences. Select Haskell in the menu and drill down to helper executables. Select the appropriately named executables for Build Wrapper and Browser Executable (for scion-browser). These are links in the bin directory, but eclipse will resolve them fine.
That should at least get syntax highlighting working.
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These instructions are applicable to EclipseFp 2.2.2 and Lion, and probably apply to other versions of OS X and EclipseFP.