Couldn't match expected type - Haskell Code
- by wvyar
I'm trying to learn Haskell, but the small bit of sample code I tried to write is running into a fairly large amount of "Couldn't match expected type" errors. Can anyone give me some guidance as to what I'm doing wrong/how I should go about this?
These are the errors, but I'm not really sure how I should be writing my code.
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 }
This is the code itself. I think it's fairly straightforward, but the idea is to run a loop, take input, and perform actions based off of it by calling other functions.
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)
Thanks, and apologies if this isn't the correct place to be asking such a question.
