ArrowHead

    Micro-framework for flowchart computing
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Arrowhead is a framework for constructing flow charts composed of steps connected by (possibly) conditional branches. Such flows can be executed, inspected (at runtime) and visualized (for documentation and verification)

The idea of flowchart computing is designed in a way that mimics a hand-made drawing, typically on a white-board or a piece of paper, that describes some process as a graph of interconnected steps.

Traditionally, once designed, the process is implemented as a collection of functions and classes. Very often the original idea of how the process was supposed to work lost, especially after making changes over time. Usually it is impossible to easily reconstruct the initial idea from a complex implementation of that idea.

As an added issue, it is non-trivial to create derivative processes that somehow override, change, replace or remove parts of the process. This can affect one step or a particular group of steps.

The arrowhead framework aims to address both problems.

The process (or flow, as some communities like to call it) is encoded as a class derived from the :class:Flow class. Inside each method decorated with the @step decorator becomes a distinct step.

Each step may connect to other steps with arrows. This can be done with the @arrow decorator. Arrows may be constrained by passing value= keyword argument. Such arrows are followed only when step.value is equal to arrow.value. Arrows may also be constrained by passing error= keyword argument. Such arrows are followed only when an exception of that (or derivative) type is raised by the step function. Arrows without either constraint are always followed.

Each flow needs to have one initial and at least one accepting step. Flow execution always starts with the initial step. The initial step can be changed in derivative classes, in that case the base initial step is no longer considered initial.