Could someone please explain why the commented line fails spectacularly while the final line succeeds?
import System.IO (getContents) import System.Environment (getArgs)
fileInput :: IO String fileInput = getArgs>>=readFirst where readFirst :: [FilePath] -> IO String readFirst [] = System.IO.getContents --readFirst xs = readFile.head xs readFirst xs = readFile $ head xs
I'm particularly confused given the following typings (from ghci): readFile.head :: [FilePath] -> IO String readFile.head [] :: a -> IO String And this is still stranger: :type readFile.head ["foo", "bar"] <interactive>:28:16: Couldn't match expected type `a0 -> FilePath' with actual type `[Char]' In the expression: "foo" In the first argument of `head', namely `["foo", "bar"]' In the second argument of `(.)', namely `head ["foo", "bar"]' <interactive>:28:23: Couldn't match expected type `a0 -> FilePath' with actual type `[Char]' In the expression: "bar" In the first argument of `head', namely `["foo", "bar"]' In the second argument of `(.)', namely `head ["foo", "bar"]' Many thanks in advance, vale