 Polyadic constructors with special case for unary constructors.
encodeArgs opts multiCons (NormalC conName ts) = do
    let len = length ts
    args <- mapM newName ["arg" ++ show n | n <- [1..len]]
    js <- case [[|toJSON|] `appE` varE arg | arg <- args] of
            -- Single argument is directly converted.
            [e] -> return e
            -- Multiple arguments are converted to a JSON array.
            es  -> do
              mv <- newName "mv"
              let newMV = bindS (varP mv)
                                ([|VM.unsafeNew|] `appE`
                                  litE (integerL $ fromIntegral len))
                  stmts = [ noBindS $
                              [|VM.unsafeWrite|] `appE`
                                (varE mv) `appE`
                                  litE (integerL ix) `appE`
                                    e
                          | (ix, e) <- zip [(0::Integer)..] es
                          ]
                  ret = noBindS $ [|return|] `appE` varE mv
              return $ [|Array|] `appE`
                         (varE 'V.create `appE`
                           doE (newMV:stmts++[ret]))
    match (conP conName $ map varP args)
          (normalB $ encodeSum opts multiCons conName js)
          []

-- Records.
e
encodeArgs opts multiCons (NormalC conName ts) = do
    let len = length ts
    args <- mapM newName ["arg" ++ show n | n <- [1..len]]
    js <- case [[|toJSON|] `appE` varE arg | arg <- args] of
            -- Single argument is directly converted.
            [e] -> return e
            -- Multiple arguments are converted to a JSON array.
            es  -> do
              mv <- newName "mv"
              let newMV = bindS (varP mv)
                                ([|VM.unsafeNew|] `appE`
                                  litE (integerL $ fromIntegral len))
                  stmts = [ noBindS $
                              [|VM.unsafeWrite|] `appE`
                                (varE mv) `appE`
                                  litE (integerL ix) `appE`
                                    e
                          | (ix, e) <- zip [(0::Integer)..] es
                          ]
                  ret = noBindS $ [|return|] `appE` varE mv
              return $ [|Array|] `appE`
                         (varE 'V.create `appE`
                           doE (newMV:stmts++[ret]))
    match (conP conName $ map varP args)
          (normalB $ encodeSum opts multiCons conName js)
          []

-- Records.
encodeArgs opts multiCons (NormalC conName ts) = do
    let len = length ts
    args <- mapM newName ["arg" ++ show n | n <- [1..len]]
    js <- case [[|toJSON|] `appE` varE arg | arg <- args] of
            -- Single argument is directly converted.
            [e] -> return e
            -- Multiple arguments are converted to a JSON array.
            es  -> do
              mv <- newName "mv"
              let newMV = bindS (varP mv)
                                ([|VM.unsafeNew|] `appE`
                                  litE (integerL $ fromIntegral len))
                  stmts = [ noBindS $
                              [|VM.unsafeWrite|] `appE`
                                (varE mv) `appE`
                                  litE (integerL ix) `appE`
                                    e
                          | (ix, e) <- zip [(0::Integer)..] es
                          ]
                  ret = noBindS $ [|return|] `appE` varE mv
              return $ [|Array|] `appE`
                         (varE 'V.create `appE`
                           doE (newMV:stmts++[ret]))
    match (conP conName $ map varP args)
          (normalB $ encodeSum opts multiCons conName js)
          []

-- Records.