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Re^5: Burned by precedence rules (== true)

by ikegami (Patriarch)
on Dec 30, 2008 at 20:09 UTC ( #733338=note: print w/replies, xml ) Need Help??

in reply to Re^4: Burned by precedence rules (== true)
in thread Burned by precedence rules

There's a logical operator for that: xor

if ( !$x == !$y) ) # bool($x) == bool($y) if ( !$x != !$y ) # bool($x) != bool($y)
can be written as
if ( !($x xor $y) ) # bool($x) == bool($y) if ( $x xor $y ) # bool($x) != bool($y)

Unforunately, both sets have readability issues.

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Re^6: Burned by precedence rules (== true)
by TimToady (Parson) on Dec 30, 2008 at 20:49 UTC
    In Perl 6 we can use positive boolean context, which helps readability a little:
    if ?$x == ?$y {...} if ?$x != ?$y {...}
    We can use junctions, which again helps the different case more than the same case:
    if not $x ^ $y {...} if $x ^ $y {...}
    or if you prefer:
    if !one($x,$y) {...} if one($x,$y) {...}
    That's probably enough ways to do it...

      Nah. Clearly this demonstrates the utility of a few "Boolean comparison" operators:

      if $isFree ?= $isEasy if $isOne !?= $isOther unlink $dev eqv unlink $prod or die "Inconsistent state"; system $verifyUser neqv system $verifyAdmin or die "You are not just either a User or an Admin";


      - tye        

        Well, we can't use eqv because we already use that for something else, but we do have a Boolean not-equal already:
        $x ?^ $y
        What we don't have is a Boolean equal. I thought about adding:
        $x ?= $y
        but people would probably think that means:
        $x = $x ? $y;
        which is nonsense, but they'd still think it. :-)

        Anyway, the utility is not worth the extra complexity, in my opinion. Comparing two Booleans for equivalence is an odd enough thing to do that I don't mind if it looks a little odd.

Re^6: Burned by precedence rules (== true)
by demerphq (Chancellor) on Dec 31, 2008 at 00:01 UTC

    Ah yes, scalar xor, i always forget about it. Personally the !$x == !$y makes more sense to me than !($x xor $y). But whatever.


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