pi (ANSI and GNU Common Lisp Document)

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#### 12.2.22 pi [Constant Variable]

#### Value::

an implementation-dependent long float.

#### Description::

The best long float approximation to the mathematical constant \pi.

#### 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 \pi 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.