Anyway i dont understand your reply. I removed :default ::= action => [name,values] and is this the root cause of the "bogus" array (it makes sense to know which name is passing around but I consider it misleading in the sysnopsis).

I read in the doc you linked:

> The "::first" action indicates that the value of a rule is to be the value of its first child, that is, the value corresponding to the first symbol of the rule's RHS.

But I cannot see how your addition of action => ::first can fix it. Given I removed the :default ::= action I get the same results with or without ::first

Dice_Expression ::= Simple_Dice
            |Dice_with_modifier_x
            |Dice_with_modifier_r

do_simple_roll received: ({}, 4, "d", 6)
        Rolled : 4
        Rolled : 3
        Rolled : 6
        Rolled : 2
do_simple_roll returning: { die_type => "1d6", rolls => [4, 3, 6, 2] }
modifier_r received: ({}, { die_type => "1d6", rolls => [4, 3, 6, 2] }
+, "r", 1)



Dice_Expression ::= Simple_Dice action => ::first 
                    |Dice_with_modifier_x action => ::first
                    |Dice_with_modifier_r action => ::first 

do_simple_roll received: ({}, 4, "d", 6)
        Rolled : 3
        Rolled : 2
        Rolled : 5
        Rolled : 6
do_simple_roll returning: { die_type => "1d6", rolls => [3, 2, 5, 6] }
modifier_r received: ({}, { die_type => "1d6", rolls => [3, 2, 5, 6] }
+, "r", 1)
[download]

L*