String Calculator in Haskell

string_calculator.hs

module StringCalculator where

import Test.Hspec
import Test.QuickCheck
import Control.Exception (evaluate)
import Data.List.Split (splitOn)

calculator' :: String -> Char -> Integer
calculator' x c = sum $ coerceString x c

calculator :: String -> Integer
calculator x =  sum $ coerceString x ','

coerceString :: String -> Char -> [Integer]
coerceString x c = map (coerce) (splitOn [c] x)
    where
        coerce "" = 0
        coerce a = read a :: Integer

main :: IO ()
main = hspec $ do
    describe "String Calculator" $ do
        it "returns 0 for empty string" $ do
            calculator "" `shouldBe` 0
        it "returns 1 for '1'" $ do
            calculator "1" `shouldBe` 1
        it "returns 2 for '2'" $ do
            calculator "2" `shouldBe` 2
        it "returns 3 for '1,2'" $ do
            calculator "1,2" `shouldBe` 3
        it "returns 6 for '1,2,3'" $ do
            calculator "1,2,3" `shouldBe` 6
        it "can accept a separator" $ do
            calculator' "1;2;3" ';' `shouldBe` 6
        it "can accept a separator" $ do
            calculator' "1ن2ن3" 'ن' `shouldBe` 6