I think that Neil \bot posted on this subject in this forum at some point with a fairly optimistic message.
Robby On Tue, Mar 4, 2014 at 11:54 AM, J. Ian Johnson <i...@ccs.neu.edu> wrote: > It's a bit of a philosophical problem to have an "exact" infinity. Writing > your own such wrappers should not be too much work. I've done similar > constructions in my own work in analysis, simply using the symbol 'ω for > infinity. > -Ian > ----- Original Message ----- > From: "Max New" <maxs...@gmail.com> > To: users@racket-lang.org > Sent: Tuesday, March 4, 2014 12:08:03 PM GMT -05:00 US/Canada Eastern > Subject: [racket] Exact Infinity? > > > > > I've been doing some work that uses a data structure that includes a size > that can be either a Natural number of Infinity ,a so-called "extended > natural number". > > > I've been using +inf.0 and gotten by using `<` and `infinite?` and things > have worked fine out of the box but now I need to take the minimum of such > numbers, but > > > > (min 0 +inf.0) > returns 0.0, an inexact 0. This behavior is expected: > http://docs.racket-lang.org/reference/generic-numbers.html?q=inf&q=min&q=min&q=list/c&q=-%3E&q=define/contract#%28def._%28%28quote._~23~25kernel%29._min%29%29because > +inf.0 (and +inf.f) is a floating point number and thus inexact. > > > I need to use exact naturals throughout however, so I can write a wrapper > that takes the floor of the number after a call to min or I can define my > own min that returns the original arguments. > > > > (define (mymin a b) > (if (< a b) a b)) > > > But would it be useful if exact infinities were added to the numeric > tower? I'll call them +inf and -inf. Most operations like +, * etc could be > defined easily though you would probably also want to add an "exact" nan > for say (+ +inf -inf). The operations would work exactly the same way they > do for inexact infinities, except returning exact numbers when possible, so > for example > > > (1 . / . +inf) ==> 0 > (min 34 +inf) ==> 34 > > > -Max Stewart New > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users >
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