Dirichlet doesn't allow basic Theano types

[brandonwillard]

The Dirichlet distribution doesn't allow basic Theano types (e.g. TensorVariable and TensorConstant) for its parameter.

The following raises a TypeError:

import numpy as np
import pymc3 as pm

import theano.tensor as tt


pm.Dirichlet.dist(tt.as_tensor_variable(np.r_[1, 1]))

the relevant output is

TypeError: The vector of concentration parameters (a) must be a python list or numpy array.