fBin :: (Double -> Double -> Double) -> [Const] -> Maybe Const
fBin op [Fl x, Fl y] = Just $ Fl (op x y)
fBin :: (Double -> Double -> Double) -> [Const] -> Maybe Const
fBin op [Fl x, Fl y] = Just $ Fl (op x y)
fBin op [Fl x, Fl y] = Just $ Fl (op x y)