Change user input to input "Char" not a "Value"? - haskell

Question

This is my code
module Main where
import Control.Monad (mapM)
import Text.Read (readMaybe)
import System.IO (BufferMode(..), stdout, hSetBuffering)
mouth = [('P',0),('(',1),('[',2),(')',3),('O',4)]
eyes = [(':',1),('8',2),(';',3)]
findKey :: (Eq k) => k -> [(k,v)] -> Maybe v
findKey key = foldr (\(k,v) acc -> if key == k then Just v else acc) Nothing
query :: Read a => String -> IO a
query prompt = do
putStr $ prompt ++ ": "
val <- readMaybe <$> getLine
case val of
Nothing -> do
putStrLn "Sorry that's a wrong value - please reenter"
query prompt
Just v -> return v
ngoers :: IO Int
ngoers = query "Enter the number of Concertgoers"
cgoers :: Int -> IO (Int, Double)
cgoers i = do
c <- query prompt
return (fromIntegral i,c)
where prompt = "Enter the emoticon for concertgoer " ++ show (i+1)
concertgoer :: IO [(Int, Double)]
concertgoer = do
n <- ngoers
mapM cgoers [0,1..n-1]
presentResult :: Double -> IO ()
presentResult v = putStrLn $ "The results are: " ++ show v
main :: IO ()
main = do
p <- concertgoer
presentResult $ 0
I want this output
Enter the number of Concertgoers: 4
Enter the emoticon for concertgoer 1: :(
Enter the emoticon for concertgoer 2: :)
Enter the emoticon for concertgoer 3: ;P
Enter the emoticon for concertgoer 4: ;o
The results are: 2 4 3 7

Answer 1

From your example I'm guessing that you match each eye and mouth to a number, and a emoticon is the sum if those... but you haven't explained nothing of this in your post. Assuming so, this is a very naive way to write It
import Control.Monad (mapM)
-- Define the data you want to use
data Eye = Normal
| Glasses
| Wink
deriving(Show, Eq)
data Mouth = P
| Sad
| Bracket
| Happy
| O
deriving(Show, Eq)
data Face = Face Eye Mouth deriving(Show, Eq)
-- Define special readers and elemToInt
readEyes :: Char -> Maybe Eye
readEyes c = case c of
':' -> Just Normal
'8' -> Just Glasses
';' -> Just Wink
_ -> Nothing
-- This is equivalent to derive Enum class and apply fromEnum. Try to do it your self ;)
eyeToInt :: Eye -> Int
eyeToInt Normal = 1
eyeToInt Glasses = 2
eyeToInt Wink = 3
readMouth :: Char -> Maybe Mouth
readMouth c = case c of
'P' -> Just P
'(' -> Just Sad
'[' -> Just Bracket
')' -> Just Happy
'O' -> Just O
_ -> Nothing
mouthToInt :: Mouth -> Int
mouthToInt P = 0
mouthToInt Sad = 1
mouthToInt Bracket = 2
mouthToInt Happy = 3
mouthToInt O = 4
readFace :: String -> Maybe Face
readFace [] = Nothing
readFace [e,m] = do
eye <- readEyes e
mouth <- readMouth m
return $ Face eye mouth
readFace _ = Nothing
faceToInt :: Face -> Int
faceToInt (Face e m) = eyeToInt e + mouthToInt m
-- The main loop is straight forward
main :: IO ()
main = do
putStrLn "Enter the number of Concertgoers"
number <- read <$> getLine -- Use safe reading better... I am using an online repl so no access to it
results <- mapM getEmoticon [1..number]
putStrLn $ "The results are: " ++ show results
where getEmoticon n = do
putStrLn $ "Enter the emoticon for concertgoer " ++ show n
face <- readFace <$> getLine
case face of
Nothing -> do
putStrLn "That's not an emotion!!"
getEmoticon n
Just f -> return $ faceToInt f
I think It is what you expect but let me know