public CFGSubtypingAPIGenerator(CFG grammar, string grammarName, bool generateFluentAPI)
{
if (!grammar.InGreibachNormalForm())
{
throw new Exception("can generate API only for grammars in Greibach normal form");
}
this.grammar = grammar;
this.grammarName = grammarName;
this.generateFluentAPI = generateFluentAPI;
}
/// <summary>
/// Transforms grammar into Greibach normal form, i.e.,
/// where productions are of the form `v ::= t s1 s2...`, `v` a variable,
/// `t` a terminal.
/// The grammar's start variable may be nullable, `v0 ::= epsilon`.
/// </summary>
/// <param name="grammar">target grammar</param>
/// <returns>grammar in Greibach normal form</returns>
public static CFG ToGreibachNormalForm(this CFG grammar)
{
if (grammar.InGreibachNormalForm())
{
return(grammar);
}
while (true)
{
grammar = grammar.RemoveEpsilonProductions().RemoveLeftRecursion();
OrderedHashSet <Production> productions = new OrderedHashSet <Production>();
foreach (Production production in grammar.productions)
{
if (production.IsEpsilonProduction() || grammar.Terminals().Contains(production.rhs[0]))
{
productions.Add(production);
}
else
{
string rhsStartVariable = production.rhs[0];
foreach (Production otherProduction in grammar.productions)
{
if (otherProduction.lhs == rhsStartVariable)
{
List <string> newRHS = new List <string>();
newRHS.AddRange(otherProduction.rhs);
newRHS.AddRange(production.rhs.Skip(1));
productions.Add(new Production(production.lhs, newRHS.ToArray()));
}
}
}
}
grammar = verifyConsistency(grammar, new CFG(grammar.startVariable, productions));
if (grammar.InGreibachNormalForm())
{
return(grammar);
}
}
}