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Re^4: A "but" operator.

by Velaki (Chaplain)
on Sep 28, 2004 at 02:37 UTC ( #394442=note: print w/ replies, xml ) Need Help??

in reply to Re^3: A "but" operator.
in thread A "but" operator.

Since "A but B" is really a conjunctive inversion, discursively it should be equivalent to "A and not B".

And since "A and not B" is equivalent to "not (if A then B)", or in other words, "not (B if A)", couldn't this be said thusly, to be perly, "B unless A"?

"Perl. There is no substitute."
Comment on Re^4: A "but" operator.
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Re^5: A "but" operator.
by dragonchild (Archbishop) on Sep 28, 2004 at 12:34 UTC
    This is where predicate logic doesn't work as well as set theory. "A but B" is actually more akin to "A minus B", where A and B are both sets. Or, in Perl,
    my @A = ( ... ); my @B = ( ... ); my %B = map { $_ => !!1 } @B; # "A but B" grep { !$B{$_} } @A;

    Which is very close to the mixin concept that Perl6 will apply to the term "but".

    Being right, does not endow the right to be rude; politeness costs nothing.
    Being unknowing, is not the same as being stupid.
    Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
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    I shouldn't have to say this, but any code, unless otherwise stated, is untested

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