particle was talking to me about reverse and not being able to get it to work in scalar context. The problem with reverse is the classic Perl scalar versus list context one. Many perl functions can return either a scalar or a list, depending on how they are called. localtime() is a common one that can return suprising results if you wanted the scalar human readable form and insted call it in list context. Reverse to exhibits some interesting behaviour on the surface. 

print "The time is ",localtime();
printf "\nor do you prefer %s\n\n", scalar localtime();

$a = "1234";
$b = "4321";
print "Hmm '$a' eq reverse '$b'\n" if $a eq reverse $b;
print "But reverse \$b = ", reverse $b;
print "\nWhich is not equal to \$a = ", $a;

# assign a scalar context to reverse
print "\n\nApplying scalar context to reverse\n";
$b = "4321";
$b = reverse $b;
print "Now \$b = '$b', which is reversed\n";
# you can assign scalar context to reverse like this to
$b = "4321";
printf "Here too reverse \$b = '%d'\n", scalar reverse $b;
printf "And also here reverse \$b = '%d'\n", eval reverse $b;

[download]

This prints: 

The time is 4434612610141920
or do you prefer Thu Jul 12 06:34:44 2001

Hmm '1234' eq reverse '4321'
But reverse $b = 4321
Which is not equal to $a = 1234

Applying scalar context to reverse
Now $b = '1234', which is reversed
Here too reverse $b = '1234'
And also here reverse $b = '1234'

In the example where reverse seems to fail it actually does not. Perl assumes list context in the print and thus reverses the one element list containing $b - this of course does not reverse the content of $b. To get it to work you need to force scalar context. It took me a while to get to grips with this behaviour.

cheers

tachyon

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In reply to Reverse in scalar context by tachyon

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