Result is that it gives is "equal". Why?

Because eq is a function with infix syntax. That is:  a eq b is actually eq( a, b ).

Thus, by the time eq() sees the parameters, both assignments have been done, and it just gets two copies of the (same) final value.

Viz

sub eq{ print "@_"; $_[0] eq $_[1] };;

print eq( $x=1, $x=2 );;
Ambiguous call resolved as CORE::eq(), qualify as such or use & at (ev
+al 13) line 1, <STDIN> line 5.
Use of uninitialized value $_ in print at (eval 13) line 1, <STDIN> li
+ne 5.

print &eq( $x=1, $x=2 );;
2 2
1
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