Tracing Factorial in Racket

• To help understand how the factorial procedure works, we can trace it:

      > (require (lib "trace.ss"))
      > (trace factorial)
      (factorial)
      > (factorial 4)
      |(factorial 4)
      | (factorial 3)
      | |(factorial 2)
      | | (factorial 1)
      | | 1
      | |2
      | 6
      |24
      24
      >

• Q: What happens if we evaluate (factorial -5)?