Remember that arguments are passed by reference*, so print will see the change in $x caused by ++ (which must be evaluated before print is called).

In detail, 

print $x, $x++;

[download]

is roughly equivalent to 

{
   local @_;
   alias $_[0] = $x;
   alias $_[1] = $x++;
   &print;
}

[download]

except the order of the alias statements isn't defined.

Given $x=0, @_ is ($x, $anon) which evaluates to (1, 0).

In short, avoid modifying a variable in a parameter list expression when the variable appears elsewhere in that parameter list.

* — "by reference" is different than "as a reference".

In reply to Re: print behavior by ikegami
in thread print behavior by Anonymous Monk

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