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Numbers and Pork Rinds

    Date: Mon, 28 Aug 89 12:35:45 EDT
    From: gls@Think.COM (Guy Steele)
    ... an implementation using IEEE arithmetic might find it completely
    convenient to have both exact and inexact floats; a result float would be
    exact if all inputs are exact AND the IEEE operation(s) reported no inexact

Quite right.  With IEEE giving you this assistance you can even consider
using -only- IEEE floats in your Scheme implementation -- using them for
both exact and inexact numbers.  This should give you an adequate range of
exact integers to index vectors and measure the lengths of lists (as well
as a random collection of exact rationals of the form M/(2^N)).  This might
even be a reasonable thing to do if you're trying to do a quick and simple
Scheme implementation.  (But if your floating point hardware -doesn't- tell
you about loss of exactness, I can't imagine making such a choice.)