Complete the following Haskell function definitions. Unless stated otherwise do not use library functions that are not in the Haskell standard prelude.

6. [2 marks] Write a function isNumber:: String -> Bool that tests if a string contains a valid number. A valid number is defined in EBNF as: number ?digit+| digith [.digit"] For example, .5, 1.5, 1, 1. are all valid numbers. As usual, -+ signifies one or more occurrences, anddenotes zero or more. You may use the isDigit function from the Data. Char module. Hint: you may wish to write functions someDigits, manyDigits: String - Bool to test for digit and digit