public bool Equals( LR0Item other )
{
return !object.ReferenceEquals(other, null) &&
this.rule.Equals(other.rule) &&
this.cursor_pos == other.cursor_pos;
}
/// <summary>
/// Calculates and returns the closure of the given canonical set.
/// </summary>
/// <param name="set">Get the closure of this set.</param>
/// <param name="grammar">The set belongs to this grammar.</param>
/// <returns>The closure of the given <paramref name="set"/>.</returns>
/// <exception cref="ArgumentNullException"> if any of the parameters is <c>null</c>.</exception>
public static ISet<LR0Item> Closure( ISet<LR0Item> set, RestrictedStartSymbolGrammar grammar )
{
if( object.ReferenceEquals(set, null) )
throw new ArgumentNullException("set");
if( object.ReferenceEquals(grammar, null) )
throw new ArgumentNullException("grammar");
var closure = new List<LR0Item>(set);
for( int i = 0; i < closure.Count; ++i )
{
var item = closure[i];
// Skip this, if the cursor pos is on the end
if( item.CursorPosition == item.Rule.RightHandSide.Count )
continue;
// Skip this, if the next_symbol is not grammatical
var next_symbol = item.Rule.RightHandSide[item.CursorPosition];
if( !(next_symbol is GrammaticalSymbol) )
continue;
// Get all the rules whit next_symbol on the left hand side
var rules = from rule in grammar.Rules
where rule.LeftHandSide.Equals(next_symbol)
select rule;
// Add all the generated RL(0) items to the closure
foreach( var rule in rules )
{
var new_item = new LR0Item(rule, 0);
if( !closure.Contains(new_item) )
closure.Add(new_item);
}
}
return new HashSet<LR0Item>(closure);
}
