Bytecode VM

[laszlokorte]

In order to simplify the implementation of stepping through the drawing instructions, setting break points, and the nesting of pictures inside each other (modeled as procedure calls) it seems like a good idea to build a simple VM layer specialized on doing vector math.

I already started to implement that here:
https://github.com/laszlokorte/reform-swift/blob/master/ReformCore/ReformCore/VM.swift

But it's just a rough sketch and it's not in use yet.

It would work as follows:

A picture consists of a Procedure containing the drawing instructions (represented as AST)
The Drawing instructions would be compiled into VM byte code
That byte code would then be executed by the VM/runtime
The result would be a list of shapes

Currently the AST is executed by the runtime directly.

Converting the AST into a linear sequence of instructions would also allow better tracking of runtime errors and preventing long running code (loops, recursion) by injecting control points into the sequence.