3.1 Implementing conditional

From the example of Section 2.1 you can just embed a condition while you run a module.

d_out1, d_out2 = m.run(when = (len(d_in.ref) < 6), false_return = (None, 0))

This example will set d_out1 to None and d_out2 to 0, but not any Data inherited type (it's up to you actually).

print x, y

The parameter when is a boolean expression and false_return is the result your module generates when the expression is False. By default when = True and false_return = None. Here, we are giving freedom to the developer for setting the output flow when the condition is False. We have to do it explicitly, because we do not know in advance how many output will be generated during the body overriding.