do notation, pattern matching, if, & case

26 Aug 2014

      I'm working on a cli program where I'd like to take input from a file
or stdin. I've managed to get my program to work but thought my
dispatch mechanism could be simplified. I use a scheme along the lines
of f in the following minimal example, which compiles. 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?

Many thanks,
vale
...
module MinimalExample where
import System.IO (getContents)
...
f :: String -> IO ()
f "-" = do
 s <- getContents
 putStrLn s
f file = do
 s <- readFile file
 putStrLn s
...
-- f' :: String -> IO ()
-- f' file = do
--   if file == "-"
--     then s <- getContents
--     else s <- readFile file
--   putStrLn s
...
-- f'' :: String -> IO ()
-- f'' file = do
--   case file of
--     "-" -> s <- getContents
--     _ -> s <- readFile file
--   putStrLn s
--
vale cofer-shabica
vale.cofershabica@gmail.com

Vale Cofer-Shabica

Brandon Allbery

Vale Cofer-Shabica

tags

participants (2)