handling Throw exception in Haskell

In Haskell, we can throw exceptions using the throw function from the Control.Exception module.

Here's an example of how to throw an exception using throw:

import Control.Exception
divideByZero :: Double -> Double -> IO Double

divideByZero x y =

  if y == 0

    then throw DivideByZero

    else return (x / y)

In this example, divideByZero function throws the DivideByZero exception if y is zero, otherwise it returns the division result of x and y.

Another example:

import Control.Exception
divideByZeroAgain :: Double -> Double -> IO Double

divideByZeroAgain x y =

  if y == 0

    then throwIO DivideByZero

    else return (x / y)

In this example, we use the throwIO function to raise the DivideByZero exception instead of throw. The throwIO function is an IO-based version of throw. It directly throws an exception inside an IO action.

Both of these examples use the DivideByZero exception type, which is already defined in the Haskell base library. However, you can create custom exception types by defining your own data types. Here's an example of a custom exception type:

data MyException = MyException String
  deriving (Show, Eq)
instance Exception MyException
raiseMyException :: IO ()

raiseMyException = throwIO (MyException "Something went wrong!")

In this example, we define a custom exception type MyException. We use instance Exception MyException to declare it as an instance of the Exception class so that we can use it with the throw or throwIO functions. And in the last, we use throwIO to throw the custom exception MyException with a message.