test.hs

{-# LANGUAGE ScopedTypeVariables #-}
module Main where
 
import Control.Exception
import System.Exit
 
main :: IO ()
main = do
    r <- catch (do
                    let [r, _] = ['a']
                    return r)
               (\(e :: PatternMatchFail) -> do
                    print "failed"
                    exitFailure
               )
    print r