Possibility for cyclic graph support?

[lcorcodilos]

Hello,

I'm curious what thoughts there are on producing graphs with cycles. I know this is essentially disallowed currently because of this line. But below is a simple example of the type of thing I'd like to be able to do.

from graphtik import compose, config, operation, optional
config.set_debug(True)

@operation(name="f1", needs=["i"], provides=["j"])
def f1(x):
    return x

@operation(name="f2", needs=["j", optional("l")], provides=["k"])
def f2(x, y=None):
    if y is None:
        return x
    return x + y

@operation(name="f3", needs=["k"], provides=["l", "m"])
def f3(x):
    if x > 5:
        return {"l": x}
    else:
        return {"m": x}

sol = compose("test", f1, f2, f3)
sol.plot("test.svg")
sol.compute({"i": 1})

This plots perfectly fine and as I'd expect but fails on sol.compute() as expected. I'm not a computational graph expert so I'm wondering if there are any fundamental blockers to supporting this type of feature. As far as I can tell, the topological sort is used just when looking for unsatisfied operations. Maybe there's another way to do this search that doesn't require the sort? Thanks for taking a look!