Example: Factorial

• n! = n × (n-1) × (n-2) × ... 2 × 1

• For example, 4! = 4 × 3 × 2 × 1 = 24

• Of course 4! is easy in Scheme:

      > (* 4 3 2 1)
      24		

• How about 52! (The number of possible outcomes of shuffling a deck of cards):

      > (* 52 51 50 ... 2 1)
      reference to undefined identifier: ... 

• We want a procedure that will take an arbitrary positive integer as an argument and compute its factorial:

      > (factorial 4)
      24
  
      > (factorial 52)
      80658175170943878571660636856403766975289505440883277824000000000000