+-- | Propagate the state into a single function application.
+-- propagateState' ::
+-- [(SignalId, SignalId)]
+-- -- ^ TODO
+-- -> SigDef -- ^ The SigDef to process.
+-- -> ([SignalId], SigDef)
+-- -- ^ Any signal ids that should become substates,
+-- -- and the resulting application.
+--
+-- propagateState' states def =
+-- if (is_FApp def) then
+-- (our_old ++ our_new, def {appFunc = hsfunc'})
+-- else
+-- ([], def)
+-- where
+-- hsfunc = appFunc def
+-- args = appArgs def
+-- res = appRes def
+-- our_states = filter our_state states
+-- -- A state signal belongs in this function if the old state is
+-- -- passed in, and the new state returned
+-- our_state (old, new) =
+-- any (old `Foldable.elem`) args
+-- && new `Foldable.elem` res
+-- (our_old, our_new) = unzip our_states
+-- -- Mark the result
+-- zipped_res = zipValueMaps res (hsFuncRes hsfunc)
+-- res' = fmap (mark_state (zip our_new [0..])) zipped_res
+-- -- Mark the args
+-- zipped_args = zipWith zipValueMaps args (hsFuncArgs hsfunc)
+-- args' = map (fmap (mark_state (zip our_old [0..]))) zipped_args
+-- hsfunc' = hsfunc {hsFuncArgs = args', hsFuncRes = res'}
+--
+-- mark_state :: [(SignalId, StateId)] -> (SignalId, HsValueUse) -> HsValueUse
+-- mark_state states (id, use) =
+-- case lookup id states of
+-- Nothing -> use
+-- Just state_id -> State state_id
+
+-- | Returns pairs of signals that should be mapped to state in this function.
+-- getStateSignals ::
+-- HsFunction -- | The function to look at
+-- -> FlatFunction -- | The function to look at
+-- -> [(SignalId, SignalId)]
+-- -- | TODO The state signals. The first is the state number, the second the
+-- -- signal to assign the current state to, the last is the signal
+-- -- that holds the new state.
+--
+-- getStateSignals hsfunc flatfunc =
+-- [(old_id, new_id)
+-- | (old_num, old_id) <- args
+-- , (new_num, new_id) <- res
+-- , old_num == new_num]
+-- where
+-- sigs = flat_sigs flatfunc
+-- -- Translate args and res to lists of (statenum, sigid)
+-- args = concat $ zipWith stateList (hsFuncArgs hsfunc) (flat_args flatfunc)
+-- res = stateList (hsFuncRes hsfunc) (flat_res flatfunc)
+