-- | Lookup a constructor via a string
readConstr :: DataType -> String -> Maybe Constr
readConstr dt str =
      case dataTypeRep dt of
        AlgRep cons -> idx cons
        IntRep      -> mkReadCon (\i -> (mkPrimCon dt str (IntConstr i)))
        FloatRep    -> mkReadCon ffloat
        CharRep     -> mkReadCon (\c -> (mkPrimCon dt str (CharConstr c)))
        NoRep       -> Nothing
  where

    -- Read a value and build a constructor
    mkReadCon :: Read t => (t -> Constr) -> Maybe Constr
    mkReadCon f = case (reads str) of
                    [(t,"")] -> Just (f t)
                    _ -> Nothing

    -- Traverse list of algebraic datatype constructors
    idx :: [Constr] -> Maybe Constr
    idx cons = let fit = filter ((==) str . showConstr) cons
                in if fit == []
                     then Nothing
                     else Just (head fit)

    ffloat :: Double -> Constr
    ffloat =  mkPrimCon dt str . FloatConstr . toRational

------------------------------------------------------------------------------
--
--      Convenience funtions: algebraic data types
--
------------------------------------------------------------------------------


-- | Test for an algebraic type
readConstr :: DataType -> String -> Maybe Constr
readConstr dt str =
      case dataTypeRep dt of
        AlgRep cons -> idx cons
        IntRep      -> mkReadCon (\i -> (mkPrimCon dt str (IntConstr i)))
        FloatRep    -> mkReadCon ffloat
        CharRep     -> mkReadCon (\c -> (mkPrimCon dt str (CharConstr c)))
        NoRep       -> Nothing
  where

    -- Read a value and build a constructor
    mkReadCon :: Read t => (t -> Constr) -> Maybe Constr
    mkReadCon f = case (reads str) of
                    [(t,"")] -> Just (f t)
                    _ -> Nothing

    -- Traverse list of algebraic datatype constructors
    idx :: [Constr] -> Maybe Constr
    idx cons = let fit = filter ((==) str . showConstr) cons
                in if fit == []
                     then Nothing
                     else Just (head fit)

    ffloat :: Double -> Constr
    ffloat =  mkPrimCon dt str . FloatConstr . toRational

------------------------------------------------------------------------------
--
--      Convenience funtions: algebraic data types
--
------------------------------------------------------------------------------


-- | Test for an algebraic type
readConstr dt str =
      case dataTypeRep dt of
        AlgRep cons -> idx cons
        IntRep      -> mkReadCon (\i -> (mkPrimCon dt str (IntConstr i)))
        FloatRep    -> mkReadCon ffloat
        CharRep     -> mkReadCon (\c -> (mkPrimCon dt str (CharConstr c)))
        NoRep       -> Nothing
  where

    -- Read a value and build a constructor
    mkReadCon :: Read t => (t -> Constr) -> Maybe Constr
    mkReadCon f = case (reads str) of
                    [(t,"")] -> Just (f t)
                    _ -> Nothing

    -- Traverse list of algebraic datatype constructors
    idx :: [Constr] -> Maybe Constr
    idx cons = let fit = filter ((==) str . showConstr) cons
                in if fit == []
                     then Nothing
                     else Just (head fit)

    ffloat :: Double -> Constr
    ffloat =  mkPrimCon dt str . FloatConstr . toRational

------------------------------------------------------------------------------
--
--      Convenience funtions: algebraic data types
--
------------------------------------------------------------------------------


-- | Test for an algebraic type