pi (Constant Variable)

Value:

an implementation-dependent long float.

Description:

The best long float approximation to the mathematical constant π.

Examples:

 ;; In each of the following computations, the precision depends
 ;; on the implementation.  Also, if `long float' is treated by
 ;; the implementation as equivalent to some other float format
 ;; (e.g., `double float') the exponent marker might be the marker
 ;; for that equivalent (e.g., `D' instead of `L').
 pi → 3.141592653589793L0
 (cos pi) → -1.0L0

 (defun sin-of-degrees (degrees)
   (let ((x (if (floatp degrees) degrees (float degrees pi))))
     (sin (* x (/ (float pi x) 180)))))

Notes:

An approximation to π in some other precision can be obtained by writing (float pi x), where x is a float of the desired precision, or by writing (coerce pi type), where type is the desired type, such as short-float.