isAlpha method
Implementation
bool isAlpha(String c) {
return (c.codeUnitAt(0) >= 'a'.codeUnitAt(0) &&
c.codeUnitAt(0) <= 'z'.codeUnitAt(0)) ||
(c.codeUnitAt(0) >= 'A'.codeUnitAt(0) &&
c.codeUnitAt(0) <= 'Z'.codeUnitAt(0)) ||
c == '_' ||
c == '&' ||
c == '|';
}