[ruby-core:68506] Seven stacks (and two questions)

The Ruby Hacking Guide says that Ruby has=E2=80=A6 seven stacks. Is it =
an implementation choice (and it could be implemented with one stack), =
or is there really a need for seven logical stacks? For example, Lua has =
one stack, and still closures with upvalues are totally possible (it=E2=80=
=99s like Ruby=E2=80=99s blocks that can reference local variables of =
their enclosing method, but it works for any function with any =
upvalues).=20

1. Is there any Ruby feature that I=E2=80=99m not aware of, and it =
justifies the need of seven stacks?

2. When does Ruby generate `getdynamic` YARV opcode? Could you provide =
me with an example source code? (I really tried to make Ruby generate =
it. No results.)

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Jakub Trzebiatowski
Computer science student
Gda=C5=84sk University of Technology