getDefinition :: Dict -> String -> Either String ProgramUnit
getDefinition dict key = case (Map.lookup key dict) of
                            Just expr -> Right expr
                            Nothing -> Left $ "Word " ++ key ++ " not defined"
getDefinition :: Dict -> String -> Either String ProgramUnit
getDefinition dict key = case (Map.lookup key dict) of
                            Just expr -> Right expr
                            Nothing -> Left $ "Word " ++ key ++ " not defined"
getDefinition dict key = case (Map.lookup key dict) of
                            Just expr -> Right expr
                            Nothing -> Left $ "Word " ++ key ++ " not defined"