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| ANSI Common Lisp 12 Numbers 12.2 Dictionary of Numbers
12.2.29 abs | Function
  Syntax: abs number absolute-value Arguments and Values: number - a number. absolute-value - a non-negative real. Description: abs returns the absolute value of number. If number is a real, the result is of the same type as number. If number is a complex, the result is a positive real with the same magnitude as number. The result can be a float even if number's components are rationals and an exact rational result would have been possible. Thus the result of `(abs #c(3 4))` can be either `5` or `5.0`, depending on the implementation. Examples:
       (abs 0)  0
       (abs 12/13)  12/13
       (abs -1.09)  1.09
       (abs #c(5.0 -5.0))  7.071068
       (abs #c(5 5))  7.071068
       (abs #c(3/5 4/5))  1 or approximately 1.0
       (eql (abs -0.0) -0.0)  true
See Also: Section 12.1.3.3 Rule of Float Substitutability Notes: If number is a complex, the result is equivalent to the following: `(sqrt (+ (expt (realpart number) 2) (expt (imagpart number) 2)))` An implementation should not use this formula directly for all complexes but should handle very large or very small components specially to avoid intermediate overflow or underflow. Allegro CL Implementation Details: None.

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