--- Indicates the legal transitions on bracket( [| |] ).
-bracketOK :: ThStage -> Maybe ThLevel
-bracketOK (Brack _ _ _) = Nothing -- Bracket illegal inside a bracket
-bracketOK stage = Just (thLevel stage + 1)
-
--- Indicates the legal transitions on splice($).
-spliceOK :: ThStage -> Maybe ThLevel
-spliceOK (Splice _) = Nothing -- Splice illegal inside splice
-spliceOK stage = Just (thLevel stage - 1)
-