So I'd hope it won't throw empty elements at me, but you never know. :)

Ah. But the way I read your sample data it already has implicit empty elements.

({ 1, 2, "three", 0, ({ "internal", "array", 0, }), "end", })
                                               ^          ^
                                               |          |
                                              Here and   Here
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If you read my original post to the end, you'd see I did indeed think about using P::RD

I did read it. I just didn't comprehend it properly. I think its cause my laptop has a small screen and after a while of using it I stop focussing properly. I need to get a monitor at home. Anyway yesterday I seemed to overlook a lot of things. Sorry about that. :-)

rule : production { $return = undef; 1; }
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? Or am I understanding you wrong?

Actually I don't think that works. (At least I tried it and it did the below, but considering my other oversights of yesterday I make no strong claims :-) It seems to be semantically equivelent to

rule : production { $return = 1; }
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As for leftop it just means you dont have to do tortured things to avoid left recursion which as far as I can tell is involved in this grammar. (I could be wrong).

Anyway, it was fun. Cheers. Oh when you benchmark dont forget failure cases as well as success. :-)

--- demerphq
my friends call me, usually because I'm late....