Sorry if you get this twice (and slightly different), but I posted it off list by mistake.
---------- Forwarded message ---------- From: Thomas Yandell <[EMAIL PROTECTED]> Date: Thu, 10 Feb 2005 10:22:44 +0000 Subject: Re: Junctive puzzles. To: Matthew Walton <[EMAIL PROTECTED]> > > What if junctions collapsed into junctions of the valid options under > > some circumstances, so > > > > my $x = any(1,2,3,4,5,6,7); > > if(is_prime($x) # $x = any(2,3,5,7) > > and is_even($x) # $x = any(2) > > and $x > 2) # $x = any() > > This is Just Wrong, IMO. How confusing is it going to be to find that > calling is_prime($x) modifies the value of $x despite it being a very > simple test operation which appears to have no side effects? > > As far as I can see it, in the example, it's perfectly logical for > is_prime($x), is_even($x) and $x > 2 to all be true, because an any() > junction was used. If an all() junction was used it would be quite a > different matter of course, but I would see is_prime() called on an > any() junction as returning true the moment it finds a value inside that > junction which is prime. It doesn't need to change $x at all. > > In a way, you're sort of asking 'has $x got something that has the > characteristics of a prime number?' and of course, $x has - several of > them, in fact (but the count is not important). > Is it perhaps the comments that are wrong, rather than the code? my $x = any(1,2,3,4,5,6,7); if(is_prime($x) # expression evaluates to any(2,3,5,7) and is_even($x) # expresion evaluates to any(2, 4, 6) # at this point the boolean expression evaluates to any(2) - is this the same as 2? and $x > 2) # expression evaluates to any(3,4,5,6,7) # so result is false # $x is still any(1,2,3,4,5,6,7) Is this right? Is the following comment correct? my $x = any(2,3,4,5) and any(4,5,6,7); # $x now contains any(4,5) Tom
