in reply to A C-like brain in a Perl-like world

You do it using a hash like this - it is rather brief :-) but that's perl for you: 

sub merge {
    my %hash;
    $hash{$_}++ for @_;
  return keys %hash;
}

sub intersection {
    my %hash;
    $hash{$_}++ for @_;
  return grep { $hash{$_} > 1 } keys %hash
}

sub lookup {
    $value = shift;
    for (@_) {
        return 1 if $value eq $_;
    }
  return 0;
}
    

@ary1 = qw( a b c d e f g );
@ary2 = qw( e f g h i j k );
print merge ( @ary1, @ary2), "\n";
print intersection ( @ary1, @ary2 ), "\n";
for ( qw( j a p h ) ) {
    print lookup( $_, @ary2) ? "$_ Found\n" : "$_ Not found\n";
}

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There is a thing called the Perl FAQ which is nine documents covering all the common stuff you will want to do like merge arrays, find intersections.....

By the way it will be a good idea to lose the TRUE FALSE habit. In perl everything is true except for:

This is really handy as it lets you do stuff like print @array if @array which will only print @array if it contains elements and is thus true or &some_func if $flag which will only call the sub if $flag is true. This also means that unless you have defined a sub sub FALSE { 0 } that when you think you return FALSE you don't. 

sub oops {
   return FALSE;
}
print "Oops 'FALSE' is true in Perl" if &oops;

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Update

CheeseLord points out a error in my understanding. Thanks!

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

Replies are listed 'Best First'.
Re: Re: A C-like brain in a Perl-like world
by CheeseLord (Deacon) on Sep 27, 2001 at 05:08 UTC

    In perl everything is true except for:

    0 (including the string equvalents "0" "0.0" etc which all evaluate to zero)

    Sorry, tachyon, but that's not quite right. "0.0" is not false in perl:

    % perl -le 'print "" ? "True" : "False"'
False
% perl -le 'print "0" ? "True" : "False"'
False
% perl -le 'print "0.0" ? "True" : "False"'
True

    [download]

    Now with new grammatical goodness! (Thanks, blakem. ;-)

    His Royal Cheeziness

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[d/l]
      Apparently Perl is not as seemless in its conversions between strings and floating point numbers as it is in its conversions between strings and integers. Because the following works:

      % perl -le '$foo=0.0; print $foo ? "True" : "False";'
False

      [download]
      but the following does not: 
      % perl -le '$foo="0.0"; print $foo ? "True" : "False";'
True

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      -----
      Be bloody, bold, and resolute; laugh to scorn
      The power of man...
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[d/l]
[select]
        Perl seems to be assuming that "0.0" is a string, which is fair enough, if that is by design, which I assume it is. "return 0.0" would from a subroutine would evaluate as false.

        Perl will convert "0.0" to a number as soon as you do anything mathematical on it. Such as: 
        perl -e '$foo = "0.0" + 0; print $foo ? "True" : "False"'

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        Which behaves as you'd expect. This reminds me of (even though it's completely different):
        perl -e 'print "I cannot add" unless 19.08 + 2.01 == 21.09'

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        If I remember correctly this comes from an early TPJ article.

        Update: removed ' from print statement - thanks tilly - That's me in hybrid Win32 cmd.exe, Linux shell quoting mode :)

        Simon Flack ($code or die)
        $,=reverse'"ro_';s,$,\$,;s,$,lc ref sub{},e;$,
        =~y'_"' ';eval"die";print $_,lc substr$@,0,3;
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[d/l]
[select]

      Hey good point! "0.0" is only zero if you force an eval on it one way or another. These are interesting: 

      print "0.0 is == 0\n" if "0.0" == 0;
$string_zero = "0.0";
print "True" if $string_zero;
print "True" if eval $string_zero;

      [download]

      cheers

      tachyon

      s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

[reply]
[d/l]

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