However, if I try to use f' or f'', I get parse errors. Three questions:
* Is there a better way of doing this
* Are stylistic changes to f really called for?
* How can/ought I correct my syntax errors?
if and case are expressions. As such they are not part of the outer "do"'s syntax; you would need a new "do" in each one. This will make more sense if you study how "do" is converted to uses of the (>>) and (>>=) operators.
Additionally you can't just use "s <- getContents" like that, since (a) "s" will go out of scope, abnd (b) with nothing following, it expands to a syntax error ("getContents >>= \s ->" with nothing after the "->"). Since if and case are expressions, you need to produce a result from them and bind it at the top level. So you really want something like:
f' :: String -> IO () f' file = do s <- if file == "-" then getContents else readFile file putStrLn s