私は Haskell を学ぼうとしていますが、私が書こうとした小さなサンプル コードで、かなりの量の "Couldn't match expected type" エラーが発生しています。私が間違っていること/これについてどうすればよいかについて、誰かが私にガイダンスを与えることができますか?
これらはエラーですが、コードをどのように記述すればよいかよくわかりません。
toDoSchedulerSimple.hs:6:14:
Couldn't match expected type `[t0]' with actual type `IO String'
In the return type of a call of `readFile'
In a stmt of a 'do' block: f <- readFile inFile
In the expression:
do { f <- readFile inFile;
lines f }
toDoSchedulerSimple.hs:27:9:
Couldn't match expected type `[a0]' with actual type `IO ()'
In the return type of a call of `putStr'
In a stmt of a 'do' block: putStr "Enter task name: "
In the expression:
do { putStr "Enter task name: ";
task <- getLine;
return inFileArray : task }
toDoSchedulerSimple.hs:34:9:
Couldn't match expected type `IO ()' with actual type `[a0]'
In a stmt of a 'do' block:
putStrLn "Your task is: " ++ (inFileArray !! i)
In the expression:
do { i <- randomRIO (0, (length inFileArray - 1));
putStrLn "Your task is: " ++ (inFileArray !! i) }
In an equation for `getTask':
getTask inFileArray
= do { i <- randomRIO (0, (length inFileArray - 1));
putStrLn "Your task is: " ++ (inFileArray !! i) }
toDoSchedulerSimple.hs:41:9:
Couldn't match expected type `[a0]' with actual type `IO ()'
In the return type of a call of `putStr'
In a stmt of a 'do' block:
putStr "Enter the task you would like to end: "
In the expression:
do { putStr "Enter the task you would like to end: ";
task <- getLine;
filter (endTaskCheck task) inFileArray }
toDoSchedulerSimple.hs:60:53:
Couldn't match expected type `IO ()'
with actual type `[String] -> IO ()'
In a stmt of a 'do' block: schedulerSimpleMain
In the expression:
do { (getTask inFileArray);
schedulerSimpleMain }
In a case alternative:
"get-task"
-> do { (getTask inFileArray);
schedulerSimpleMain }
これはコードそのものです。かなり簡単だと思いますが、ループを実行し、入力を受け取り、それに基づいて他の関数を呼び出してアクションを実行するという考え方です。
import System.Random (randomRIO)
import Data.List (lines)
initializeFile :: [char] -> [String]
initializeFile inFile =
do f <- readFile inFile
let parsedFile = lines f
return parsedFile
displayHelp :: IO()
displayHelp =
do putStrLn "Welcome to To Do Scheduler Simple, written in Haskell."
putStrLn "Here are some commands you might find useful:"
putStrLn " 'help' : Display this menu."
putStrLn " 'quit' : Exit the program."
putStrLn " 'new-task' : Create a new task."
putStrLn " 'get-task' : Randomly select a task."
putStrLn " 'end-task' : Mark a task as finished."
putStrLn " 'view-tasks' : View all of your tasks."
quit :: IO()
quit =
do putStrLn "We're very sad to see you go...:("
putStrLn "Come back soon!"
createTask :: [String] -> [String]
createTask inFileArray =
do putStr "Enter task name: "
task <- getLine
return inFileArray:task
getTask :: [String] -> IO()
getTask inFileArray =
do i <- randomRIO (0, (length inFileArray - 1))
putStrLn "Your task is: " ++ (inFileArray !! i)
endTaskCheck :: String -> String -> Bool
endTaskCheck str1 str2 = str1 /= str2
endTask :: [String] -> [String]
endTask inFileArray =
do putStr "Enter the task you would like to end: "
task <- getLine
return filter (endTaskCheck task) inFileArray
viewTasks :: [String] -> IO()
viewTasks inFileArray =
case inFileArray of
[] -> do putStrLn "\nEnd of tasks."
_ -> do putStrLn (head inFileArray)
viewTasks (tail inFileArray)
schedulerSimpleMain :: [String] -> IO()
schedulerSimpleMain inFileArray =
do putStr "SchedulerSimple> "
input <- getLine
case input of
"help" -> displayHelp
"quit" -> quit
"new-task" -> schedulerSimpleMain (createTask inFileArray)
"get-task" -> do (getTask inFileArray); schedulerSimpleMain
"end-task" -> schedulerSimpleMain (endTask inFileArray)
"view-tasks" -> do (viewTasks inFileArray); schedulerSimpleMain
_ -> do putStrLn "Invalid input."; schedulerSimpleMain
main :: IO()
main =
do putStr "What is the name of the schedule? "
sName <- getLine
schedulerSimpleMain (initializeFile sName)
ありがとうございます。このような質問をするのが適切でない場合はお詫び申し上げます。