(please correct here me if I'm wrong)
I don't know if perl's documentation defines (as a feature) the order in which arguments are evaluated, but it's simple to check that it really does evaluate them in left-to-right order: 
$ perl -le 'print sub{print 1; "x"}->(), sub{print 2; "y"}->()'
1
2
xy

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The reason the OP's example is weird is because Perl's argument passing uses aliases whenever possible (as ikegami illustrates below). In the example, an alias to $| gets passed as the second argument. When evaluating the fourth argument, $| is changed. When print finally inspects its arguments, the aliased second argument will report the changed value.

blokhead

In reply to Re^2: Puzzling $| behavior by blokhead
in thread Puzzling $| behavior by saintmike

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