I have code something like this
main :: [[String]] -> IO ()
main st = do
answer <- getLine
case answer of
"q" -> return ()
"load" x -> main $ parseCSV $ readFile x
This doesn't work, so my question is how can I use case switch statement for something of changing input For example in my code I want the input from a user to be either q or a load, but the load will constant change:
load "sample.csv"
load "test.csv"
load "helloworld.csv"
In my code I indicated the constantly changing input as X, but this doesn't work as I expected it.
Help would be appreciated, thank you.
As others have mentioned, the problem is with your pattern matching.
Here's a simple way to get around this (and still have something readable).
answer
into words for matching (with the words
function). unwords
the remaining elems in the list to get a string. Example:
main :: IO ()
main = do
answer <- getLine
case words answer of
("q":_) -> putStrLn "I'm quitting!"
("load":x) -> putStrLn ("Now I will load " ++ unwords x)
otherwise -> putStrLn "Not sure what you want me to do!"
Note - the x
you had above is actually unwords x
here.
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