p_strLen, p_strHead, p_strTail, p_strIndex, p_strCons, p_strRev, p_strSubstr :: [Const] -> Maybe Const
p_strLen [Str xs] = Just $ I (length xs)
p_strLen, p_strHead, p_strTail, p_strIndex, p_strCons, p_strRev, p_strSubstr :: [Const] -> Maybe Const
p_strLen [Str xs] = Just $ I (length xs)
p_strLen [Str xs] = Just $ I (length xs)