Think of a while node type

[vijayvammi]

There is a need to simulate:

while until_condition:
   execute_branch()
   test_condition()

The until_condition should be based of a parameter that the user can control.

The results generated in that loop have to be handled carefully. They would then be a list by default but could be changed by a custom function. What about the catalog items, we need to be careful not to overwrite them.

Class While:
   branch: Graph
   until: parameter
   reducer: function

There should be a RUNNABLE_LOOP_INDEX available as env variables to the executables.