(guile.info.gz) Numerical Tower

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 21.2.1 Scheme's Numerical "Tower"
 ---------------------------------
 
 Scheme's numerical "tower" consists of the following categories of
 numbers:
 
    * integers (whole numbers)
 
    * rationals (the set of numbers that can be expressed as P/Q where P
      and Q are integers)
 
    * real numbers (the set of numbers that describes all possible
      positions along a one dimensional line)
 
    * complex numbers (the set of numbers that describes all possible
      positions in a two dimensional space)
 
    It is called a tower because each category "sits on" the one that
 follows it, in the sense that every integer is also a rational, every
 rational is also real, and every real number is also a complex number
 (but with zero imaginary part).
 
    Of these, Guile implements integers, reals and complex numbers as
 distinct types.  Rationals are implemented as regards the read syntax
 for rational numbers that is specified by R5RS, but are immediately
 converted by Guile to the corresponding real number.
 
    The `number?' predicate may be applied to any Scheme value to
 discover whether the value is any of the supported numerical types.
 
  -- Scheme Procedure: number? obj
  -- C Function: scm_number_p (obj)
      Return `#t' if OBJ is any kind of number, else `#f'.
 
    For example:
 
      (number? 3)
      =>
      #t
 
      (number? "hello there!")
      =>
      #f
 
      (define pi 3.141592654)
      (number? pi)
      =>
      #t
 
    The next few subsections document each of Guile's numerical data
 types in detail.
 

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