Tuesday, April 21, 2009

IronPython a Configuration Language

Simon Taylor, inspired by IronPython in Action no less, has written an article on embedding IronPython to create custom state machines for different customer requirements in an application.
I had a requirement to create a state machine for a product at work. The product is a project management tool and therefore has the concept of a job which based on the users actions moves from one state to another. There was also the additional requirement that the state machine should be configurable by/for different customers. Esentially, the state machine is a large flow diagram but the implementation needed to allow for completely ripping up the first customers flow diagram and replacing it with a completely different one for the next customer.

From the C# prototype I created I had a number of helper methods for doing things to manipulate my job business entity and even create a project in project server! I didn't really want to throw this away, so I didn't - I created an abstract class and then implemented the subclass in IronPython.

To do this I needed to import the classes from my C# code which I will be using (such as Job) and then subclass my StateMachine abstract class and implement the Transition abstract method. You will notice the reference to self in the Transition methods parameter list which basically means that it is an instance method.

In order to be able to use the IronPython implementation of the state machine, I needed to read in the code, essentially compile it and then keep a handle to the state machine so that I could use it at some point in the future.

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