pattern function
Returns a parser that accepts a single character of a given character set provided as a string.
Characters match themselves. A dash -
between two characters matches the
range of those characters. A caret ^
at the beginning negates the pattern.
For example, the parser pattern('aou')
accepts the character 'a', 'o', or
'u', and fails for any other input. The parser pattern('1-3')
accepts
either '1', '2', or '3'; and fails for any other character. The parser
`pattern('^aou') accepts any character, but fails for the characters 'a',
'o', or 'u'.
Implementation
@useResult
Parser<String> pattern(String element, [String? message]) =>
SingleCharacterParser(_pattern.parse(element).value,
message ?? '[${toReadableString(element)}] expected');