-- | Determines how many active choices are available in a node. Note that we
-- count goal choices as having one choice, always.
choices :: Tree a -> Int
choices (PChoice    _ _     ts) = P.length (P.filter active ts)
choices :: Tree a -> Int
choices (PChoice    _ _     ts) = P.length (P.filter active ts)
choices (PChoice    _ _     ts) = P.length (P.filter active ts)