General properties for queuing multihistory elements

[maxitg]

The problem

Many of the properties just need to extract lists of various elements. For example, "FinalState" extracts the list of expressions at the final state represented by their atoms content.

We need generic functions that would extract such sets of elements based on specified conditions.

Possible solution

The syntax should probably be:

evolution["ExpressionsList", "Atoms", "StateAfterGeneration", 4]

• The first argument tells what kind of elements to return. It could be "ExpressionsList", "AtomsList", "EventsList", etc.
• The second argument is the representation of the returned elements. It can be in terms of "Atoms", "Expressions", "Events", etc.
• The third argument is the selection function. It can be All, "StateAfterGeneration", "StateAfterEvent", "Generation", "FinalState", "EvolutionBeforeEvent", etc.
• And after that, it's the arguments for the selection function.

The example above would be equivalent to

evolution["Generation", 4]

or

evolution["ExpressionsList", "Expressions", "StateAfterEvent", 3]

would be equivalent to

evolution["StateEdgeIndicesAfterEvent", 3]

[maxitg]

We are planning to implement this in Project Yellowstone (v 0.4), however, the API will be quite different. This issue needs to be updated with the new API.