alphaNum function
Parses a single alphanumeric character.
Implementation
Parser<ParseError, String> alphaNum() => satisfy(
(c) =>
(c.compareTo('0') >= 0 && c.compareTo('9') <= 0) ||
(c.compareTo('a') >= 0 && c.compareTo('z') <= 0) ||
(c.compareTo('A') >= 0 && c.compareTo('Z') <= 0),
'alphanumeric',
);