-- Later: combine with IO monad for stable names.

import Flatten
import Control.Monad.State

-- import System.IO.Unsafe
-- import System.Mem.StableName



---- Monad versions ----

-- The foldable function wrapped in a State monad with unit output.
-- This might only be useful when combined with the IO monad for
-- stable names.
type DictUpdate n v = State ([v], [(Graph n v, v)]) ()
dictExtendState :: (Eq v, Eq n) => Graph n v -> DictUpdate n v
dictExtendState node = State tx where
    tx s = ((), dictExtend s node)

-- Dictionary accumulation then happens as a side effect of chaining
-- the update function above, mapped over the nodes.
nameNodesState vars expr = dict where
    (_, (_, dict)) = 
        (runState $ sequence $ fmap dictExtendState $ nodes expr) (vars,[])