readRational.purs

readRational :: String -> Maybe Rational
readRational = (<|>) <$> withPoint <*> withSlash
  where
  withPoint =
    String.split (String.Pattern ".")
    >>> traverse Int.fromString
    >=> case _ of
          [a]    -> Just $ a % 1
          [a, b] -> Just $ a % 1 + b % 10
          _      -> Nothing
  withSlash =
    String.split (String.Pattern "/")
    >>> traverse Int.fromString
    >=> case _ of
          [a]    -> Just $ a % 1
          [a, b] -> Just $ a % b
          _      -> Nothing