Perl 6
Default SMOP Interpreter Implementation: Revision 1
The default SMOP Interpreter Implementation is a mixture of a stack-based and a stackless machine, as it does support pushing new frames, but it also supports continuation passing style inside itself. This implementation is based on three elements:

* A Node prototype and its instances
* A Stack prototype and its instances
* Lowlevel operators that manipulate the Stack

^ Node Prototype

The Node prototype just declares an object that have a set of members.

* responder
* identifier
* capture
* debug
* jail
* lexical
* outer
* continuation
* past
* result

This members can be passed to as named arguments.

^ Stack Prototype

The Stack prototype defines the implementation in itself, it's the one with the "eval" method. It simply have a reference to the currently selected Node, and have the following methods.

* new(SMOP__STACK__Stack: $initial_node?) -- creates a new stack object, optionally defining a initial node.
* push($stack: $node) -- push the node to the stack, saving the older node as the new node's outer node.
* continues($stack: $node) -- set the given node as a continuation to the current node.
* next($stack: ) -- goes to the next node in the stack, possibly drop frames.
* current($stack: ) -- returns the currently selected node.
* goto($stack: $node) -- sets the node as the currently selected node.
* eval($stack: ) -- evaluates the currently selected node and stores the result in the result field of the node.
* result($stack: $count) -- gets the result of the past node that is $count away from the current node.
* has_next($stack: ) -- returns true if there's any more node to eval.
* loop($stack: ) -- iterates in the stack and return when has_next is false.

^^^ Stack transformations

Some of the above methods transform the stack in interesting ways. Follows some ascii diagrams on how that works.

^^^^ push

Current Frame 1 <- 2 <- 3 -> 4 -> 5

New Frame given node
Current Frame 1 <- 2 <- 3 -> 4 -> 5

^^^^ next

* *
1 <- 2 -> 3 turns into 1 <- 2 <- 3
| |


1 <- 2 <- 3 turns into
| *
1 <- 2 1 <- 2

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