/// <summary>
/// Computes the FIRSTS set for this rule body
/// </summary>
/// <returns><c>true</c> if there has been modifications</returns>
public bool ComputeFirsts(RuleChoice next)
{
// If the choice is empty : Add the ε to the Firsts and return
if (parts.Count == 0)
{
return(setFirsts.Add(Epsilon.Instance));
}
Symbol symbol = parts[0].Symbol;
// If the first symbol in the choice is a terminal : Add terminal as first and return
var terminal = symbol as Terminal;
if (terminal != null)
{
return(setFirsts.Add(terminal));
}
// Here the first symbol in the current choice is a variable
Variable variable = symbol as Variable;
bool mod = false; // keep track of modifications
// foreach first in the FIRSTS set of the variable
foreach (Terminal first in variable.Firsts)
{
// If the symbol is ε
if (first == Epsilon.Instance)
{
// Add the Firsts set of the next choice to the current Firsts set
mod |= setFirsts.AddRange(next.setFirsts);
}
else
{
// Symbol is not ε : Add the symbol to the Firsts set
mod |= setFirsts.Add(first);
}
}
return(mod);
}
/// <summary>
/// Append the specified choice
/// </summary>
/// <param name="choice">A choice</param>
public void Append(RuleChoice choice)
{
parts.AddRange(choice.parts);
}