/// <summary>
/// Tries to parse the given specifier into an Atom. For that all categories of Atoms are checked in the following order:
/// 1. Group
/// 2. Class
/// 3. Literal
/// When it succeeds, the given expression will be assigned a SingleAtomExpression containing the Atom and it's Quantifier.
/// The parsed atom will be removed from the specifier and the method returns true. To check whether the complete specifier was an Atom,
/// one needs to examine the specifier after calling this method. If it was, the specifier is empty after calling.
/// </summary>
/// <param name="specifier">The specifier to extract the leading Atom out of. Will be shortened if an Atom was successfully extracted</param>
/// <param name="expression">The resulting SingleAtomExpression</param>
/// <returns>True, if an Atom could be extracted, false otherwise</returns>
// Note: could be rewritten to not consume the specifier and instead return an integer specifying the consumed length of specifier. This would remove the by-ref passed string hack
// internal for testing
internal static bool TryParseAsAtom(ref string specifier, out IRegularExpression expression)
{
Match m = groupWithQuantifier.Match(specifier);
if (m.Success)
{
string atom = m.Groups["expression"].Value;
string quantifier = m.Groups["quantifier"].Value;
specifier = specifier.Substring(atom.Length + 2 + quantifier.Length);
expression = new SingleAtomExpression(new Group("(" + atom + ")", new Quantifier(quantifier)));
return(true);
}
m = characterClassWithQuantifier.Match(specifier);
if (m.Success)
{
string atom = m.Groups["expression"].Value;
string quantifier = m.Groups["quantifier"].Value;
specifier = specifier.Substring(atom.Length + 2 + quantifier.Length);
expression = new SingleAtomExpression(new CharacterClass("[" + atom + "]", new Quantifier(quantifier)));
return(true);
}
m = literalWithQuantifier.Match(specifier);
if (m.Success)
{
string atom = m.Groups["expression"].Value;
string quantifier = m.Groups["quantifier"].Value;
specifier = specifier.Substring(atom.Length + quantifier.Length);
expression = new SingleAtomExpression(new Literal(atom, new Quantifier(quantifier)));
return(true);
}
expression = null;
return(false);
}
public override bool Equals(object obj)
{
if (obj is SingleAtomExpression)
{
SingleAtomExpression other = obj as SingleAtomExpression;
return(other.Atom.Equals(Atom) && other.Quantifier.Equals(Quantifier));
}
return(false);
}