CODEWITHSUNDEEP
haskell
buck
buck

Reputation: 64

Haskell issue (Couldn't match type 'IO Integer' with 'Int')

I have a problem with a Haskell script. I'm trying to learn Haskell through doing problems I find online. The input I get is: Int -> Number of test cases S1 -> String 1 for each test case S2 -> String 2 for each test case

Each S1 and S2 is a space delimited string of numbers. I convert them to a list of Ints with the function strToIntList. I then want to process the two lists and return an integer value based on the results. I get the following error: Couldn't match type 'IO Integer' with 'Int' on line 24 and I stared for ages but just can't figure out why (full error at end of post).

If someone could explain why I'm going wrong, I would be very grateful.

This is my script:

import Data.List
import Data.List.Split

main = do
    cases <- readLn
    doLoop cases

toInt x = read x :: Int

strToIntList s = [read x :: Int | x <- (splitOn " " s)]

minOfTwo :: Int
minOfTwo = do
    sa <- getLine
    sb <- getLine
    return $ minimum [1..50]
    -- return $ minimum $ strToIntList sa

doLoop 0 = return ()
doLoop loopIndex = do
    q <- getLine
    let c = minOfTwo
    print(c)
    doLoop (loopIndex-1)

This is the full error I'm getting:

Couldn't match type `IO Integer' with `Int'
Expected type: IO String -> (String -> IO Integer) -> Int
  Actual type: IO String -> (String -> IO Integer) -> IO Integer
In a stmt of a 'do' block: sa <- getLine
In the expression:
  do { sa <- getLine;
       sb <- getLine;
       return $ minimum [1 .. 50] }
In an equation for `minOfTwo':
    minOfTwo
      = do { sa <- getLine;
             sb <- getLine;
             return $ minimum [1 .. 50] }

Upvotes: 1

Views: 1990

Answers (1)

MathematicalOrchid
MathematicalOrchid

Reputation: 62818

The getLine function is in the IO monad, and therefore any function that calls getLine must also be in the IO monad. Change your type signature for minOfTwo from Int to IO Int, and that particular problem will go away.

(You'll also need to change let c = minOfTwo into c <- minOfTwo.)

There may be other errors, but this is the one causing your error message.

Upvotes: 3

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