an implementation-dependent long float.

The best long float approximation to the mathematical constant π.

;; 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)))))

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.