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 21.2.2 Integers
 ---------------
 
 Integers are whole numbers, that is numbers with no fractional part,
 such as 2, 83 and -3789.
 
    Integers in Guile can be arbitrarily big, as shown by the following
 example.
 
      (define (factorial n)
        (let loop ((n n) (product 1))
          (if (= n 0)
              product
              (loop (- n 1) (* product n)))))
 
      (factorial 3)
      =>
      6
 
      (factorial 20)
      =>
      2432902008176640000
 
      (- (factorial 45))
      =>
      -119622220865480194561963161495657715064383733760000000000
 
    Readers whose background is in programming languages where integers
 are limited by the need to fit into just 4 or 8 bytes of memory may find
 this surprising, or suspect that Guile's representation of integers is
 inefficient.  In fact, Guile achieves a near optimal balance of
 convenience and efficiency by using the host computer's native
 representation of integers where possible, and a more general
 representation where the required number does not fit in the native
 form.  Conversion between these two representations is automatic and
 completely invisible to the Scheme level programmer.
 
  -- Scheme Procedure: integer? x
  -- C Function: scm_integer_p (x)
      Return `#t' if X is an integer number, else `#f'.
 
           (integer? 487)
           =>
           #t
 
           (integer? -3.4)
           =>
           #f
 

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