Whitespace only
A couple of small refactorings
Remove an out-of-date comment
Improve an error message; fixes #984

This code:
    f _ = do
            x <- computation
            case () of
                    _ ->
                            result <- computation
                            case () of () -> undefined
Now gives this error:
    Parse error in pattern: case () of { _ -> result }
    Possibly caused by a missing 'do'?