chickadee » srfi-196 » numeric-range

Returns a numeric range, a special case of a range specified by an inclusive lower bound start, an exclusive upper bound end, and a step value (default 1), all of which can be exact or inexact real numbers.

This constructor produces the sequence

start, (+ start step), (+ start (* 2 step)), …, (+ start (* n step)),

where n is the greatest integer such that (+ start (* n step)) < end if step is positive, or such that (+ start (* n step)) > end if step is negative. It is is an error if an n satisfying this condition cannot be determined, or if step is numerically zero. This procedure runs in O(1) time. The average accessing time of the resulting range is O(1).

Note that an effect of this definition is that the elements of a range over inexact numbers are enumerated by multiplying the index by the step value rather than by adding the step value to itself repeatedly. This reduces the likelihood of roundoff errors.

Examples:

(range->list (numeric-range 0 1 1/10))
  ⇒ (0 1/10 1/5 3/10 2/5 1/2 3/5 7/10 4/5 9/10)

(range->list (numeric-range 5 -5 -3)) ⇒ (5 2 -1 -4)