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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.

 integer? x Scheme Procedure scm_integer_p (x) C Function
 Return #t if x is an integer number, else #f. (integer? 487) => #t (integer? -3.4) => #f