[This is a resend; I tried to post through gmane but the message never arrived.] There is a bug in System.Console.GetOpt causing it to mistakenly reject options as ambiguous. Testcase:

import System.Console.GetOpt

type Color = String

optsDesc :: [OptDescr Color] optsDesc = [Option "" ["color", "colour"] (ReqArg id "color") "Foreground color"]

main = do let args = ["--col=blue"] case getOpt RequireOrder optsDesc args of (_, _, err:_) -> putStrLn err _ -> return ()

Output: option `--col' is ambiguous; could be one of: --color=color, --colour=color Foreground color --color=color, --colour=color Foreground color This error is silly, because the two alternatives listed are the same option. The problem is caused by incorrect use of a generator in a list comprehension. I've attached a patch that fixes the problem. Regards, Eelis