Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!sdd.hp.com!news.cs.indiana.edu!arizona.edu!arizona!gudeman From: gudeman@cs.arizona.edu (David Gudeman) Newsgroups: comp.lang.misc Subject: Re: Dynamic typing (part 3) Message-ID: <815@optima.cs.arizona.edu> Date: 19 Mar 91 08:08:09 GMT Sender: news@cs.arizona.edu Lines: 30 In article Peter da Silva writes: ]But if you don't know that y is complex, you don't know if "y <= 0" is ]legal or not... If you don't know the length of A, you don't know whether "A[i]" is legal or not. So? You should know the length of A and you should know the type of y. In someone elses code, if you see "y <= 0", then you can assume that y is not complex. In you own code, if you know that y is not complex you can write "y <= 0". There is no ambiguity. ]with this in mathematics is everyone has had a bunch of Fortran-style' ]default typing rules programmed into their head in college. No, the reason you can get away with this in math is that everyone who has a clue knows that you can't compare magnitudes of complex numbers, so if you are comparing magnitudes, the numbers must not be compex. This is a trivial logical inference: (1) y is complex implies "y <= 0" is not meaningful (2) "y <= 0" is meaningful therefore (3) y is not complex There is nothing sloppy or ambiguous about this reasoning. -- David Gudeman gudeman@cs.arizona.edu noao!arizona!gudeman