import Control.Exception
import GHC.Stack

headWithoutCS :: [a] -> a
headWithoutCS = head

headWithCS :: HasCallStack => [a] -> a
headWithCS = head

nil :: [()]
nil = []

main :: IO ()
main = do
  putStrLn "Doesn't include 'headWithoutCS' in the stack:"
  evaluate (headWithoutCS nil) `catch` \(SomeException e) -> print e
  putStrLn ""
  putStrLn "Does include 'headWithCS' in the stack:"
  evaluate (headWithCS nil) `catch` \(SomeException e) -> print e