Proof: If the comma operator. In scalar context it evaluates its left argument, throws that value away, then evaluates its right argument and returns that value..., then this should print undef or null or nothing, but it doesn't:

You left of binary. The latter comma in

scalar(1,2,3,)
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doesn't have an operand on its right hand side, so it cannot be a "binary comma".

In Perl, there isn't something like an "empty statement (or expression)" which would return 'undef'. If there was, then

    sub foo {1;}
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wouldn't return 1, but undef or null or nothing.