"Stopped in <exception thrown>, <unknown>
_exception :: e = _
Logged breakpoint at QSort.hs:6:24-38
_result :: [Char]
a :: Char
as :: [Char]
Printing 1
as = 'b' : 'c' : (_t1::[Char])
Forcing
*** Exception: Prelude.undefined
CallStack (from HasCallStack):
  error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err
  undefined, called at <interactive>:3:17 in interactive:Ghci1
Printing 2
as = 'b' : 'c' : (_t2::[Char])