Write a lexical analyzer for Pascal. These functions are provided.
Identifiers begin with a letter, followed by any number of letters or digits.
Strings are enclosed by ' characters. The character ' may be included within a string by doubling it, as in the example 'don''t' . For simplicity, we will assume that a string has at most 15 characters. The lexical analyzer must convert a number to internal numeric form. Care must be taken to ensure that the result is numerically accurate and that errors such as numeric overflow are detected.