Why PHP should never be taught.

Suppose A equals B, and also B equals C. Any reasonable person would expect that A equals C, right?

Oh yeah?

% cat equality.php
<?php

$a = 0;
$b = "eggs";
$c = "spam";

print ($a == $b) ? "a == b\n" : "a != b\n";
print ($b == $c) ? "b == c\n" : "b != c\n";
print ($a == $c) ? "a == c\n" : "a != c\n";
print ($a == $d) ? "a == d\n" : "a != d\n";
print ($b == $d) ? "b == d\n" : "b != d\n";
print ($c == $d) ? "c == d\n" : "c != d\n";

?>

% php equality.php
a == b
b != c
a == c
a == d
b != d
c != d

%

Update (2007-12-11): It gets even worse. Check this out.