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(guile.info)Integers

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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.

 - primitive: integer? obj
     Return `#t' if OBJ is an integer number, `#f' else.

          (integer? 487)
          =>
          #t
          
          (integer? -3.4)
          =>
          #f