Re: Reading infinity

From: Lars Thomas Hansen <lth_at_ccs.neu.edu>
Date: Thu, 03 Oct 96 09:43:40 -0400

>> David Fox writes
>> Is there any way to read and write infinity or minus infinity? I
>> supose I could check each number and write the value shown above it it
>> was too big.
>
>No there is not yet. What about #+inf and #-inf?
>I put it on my TODO list.

In the spirit of compatibility, could you consider making the syntax
compatible with an existing system? :-) A quick survey shows that

Chez Scheme +inf.0 -inf.0
MacScheme Student Edition 3.0 #<INFINITY> -#<INFINITY>
                                (output only)
PC Scheme (Geneva 4.0) Cannot compute infinities (gives error)
Scsh Has inexact bignums (no infinities :-)
MacGambit 2.2.2 Uses largest flonum as an alias for this
Larceny 0.25 +inf.0 -inf.0

(Popular implementations I can't get to at the moment that one might
want to check: MIT Scheme, Gambit-C, MzScheme/Rice Scheme, Scheme->C,
SCM, Bigloo.)

Furthermore, for reference,

Clisp Cannot compute infinities (gives error)
Allegro Common Lisp 4.2 (Sun) #.EXCL::*INFINITY-SINGLE*
                                (also as input)

Of the three commercial Scheme systems mentioned above, only Chez Scheme
supports reading of infinities, and it is the only one actively being
developed, and I think that forms precedent of some kind (which is why
Larceny has adopted the same convention). Not the least, this syntax
lends itself to represent infinite complexes, e.g. +inf.0+1.0i or
-3.0-inf.0i. I would make an argument, therefore, that in the spirit of
compatibility and portability you pick the same syntax as Chez Scheme.

--lars
Received on Thu Oct 03 1996 - 19:09:16 CEST