I have an (admittedly awkward) script which can be compiled or interpreted.

If it's compiled, I want the full goodness. If it's interpreted, I want to run a "minimal" version (because if I don't have the compiled version, I probably don't have the required libraries either).

The following almost works:

module Main (main) where
#ifdef FANCY
import qualified System.Console.ANSI as Term
start = Term.setSGR [Term.SetColor Term.Foreground Term.Dull Term.Green]
end = Term.setSGR []
#else
start = return ()
end = return ()
#endif
main :: IO ()
main = do
	start
	putStrLn "hello world"
	end

and then I can do:

$ runghc -cpp main.hs
hello world
^^ plain text

$ ghc -O -cpp -DFANCY main.hs
$ ./main
hello world
^^ green text (a.k.a "fancy")

I attempted to make this directly runnable by adding a shebang line of

{{{ #!/usr/bin/runghc -cpp }}}

But unfortunately that chokes with -cpp:

$ ghc -O -cpp -DFANCY main.hs

main.hs:1:0:  error: invalid preprocessing directive #!