> Thats not really much overhead, because when mixing AND and OR parens should always be applied to highlight precedence.

I would agree about the parens but there is a certain cognitive overhead in disassembling (or creating) the reverse polish notation which I have always shied away from. In the end for complicated expressions I think (I would have to check as it's been a while) I went for a mix of arrayrefs and hashrefs (implicit AND):

    select => [qw/expr1 expr2/],
    from   => 'table',
    where  => [
        { number => 3 }, OR,
        { 'customer LIKE' => '%...%', name => [qw/John Jane/] },
    },
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I'm looking forward to seeing what you come up with. Please post it!