Basic Predicates - NULL?

• We need to be able to test if a list is empty

  • we use NULL? for this, e.g.,
    • (null? '(a b c))
      #F
    • (null? '())
      #T
  • Scheme and LISP often use the empty list, (), to denote falsity, e.g., you may sometimes see
    • (null? '(a b c))
      ()
  • In LISP, the special atom, NIL, also stands for the empty list

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