*** Exception: Prelude.head: empty list
CallStack (from HasCallStack):
  error, called at libraries/base/GHC/List.hs:1590:3 in base:GHC.List
  errorEmptyList, called at libraries/base/GHC/List.hs:74:11 in base:GHC.List
  badHead, called at libraries/base/GHC/List.hs:70:28 in base:GHC.List
  head, called at <interactive>:1:10 in interactive:Ghci1
*** Exception: Prelude.undefined
CallStack (from HasCallStack):
  undefined, called at <interactive>:1:17 in interactive:Ghci1