allow custom action selection criteria

[zsunberg]

We should allow the user to specify a custom action selection criterion like in POMCPOW

[simon-lc]

Hey! I'm trying to add an action selection criterion. I would like to have a set of available actions for each node defined by: actions(pomdp, belief) or actions(pomdp, s). With the belief computed via the history of actions and observations (h in "Monte-Carlo Planning in Large POMDPs") and s a state that is a particle in the set B(h).
I implemented POMDPs.actions(pomdp, s). However when I run the BasicPOMCP solver actions are selected in the set defined by POMDPs.actions(pomdp). Is there a way to force the solver to use actions(pomdp, s) or a function like actions(pomdp, belief) instead of actions(pomdp).

[MaximeBouton]

This is related to JuliaPOMDP/POMDPs.jl#226.

Note that the function insert_obs_node! that is calling actions does not have access to a state nor the belief.

[simon-lc]

Thanks for the redirection!
You're right insert_obs_node! only has access to the observation.