public Parser(CFG grammar, Terminal syncTerm)
{
this.grammar = grammar;
this.table = grammar.CreateLL1ParseTable();
this.start = grammar.StartSymbol;
this.syncTerm = syncTerm;
if (table == null)
throw new Exception("GRAMMAR NOT LL(1)");
}
public Parser(CFG grammar, Terminal syncTerm)
{
this.grammar = grammar;
this.table = grammar.CreateLL1ParseTable();
this.start = grammar.StartSymbol;
this.syncTerm = syncTerm;
if (table == null)
{
throw new Exception("GRAMMAR NOT LL(1)");
}
}
// Builds an LL(1) parse table using the First and Follow sets for the grammar
// returns null if CFG is not LL(1)
public ParseTable CreateLL1ParseTable()
{
ComputeFirstSets();
ComputeFollowSets();
if (Program.debug)
Console.WriteLine("=========================================================");
ParseTable parseTable = new ParseTable();
// for each nonterminal in the grammar and each production rule for the nonterminal
foreach (Nonterminal var in productions.Keys)
{
foreach (ISymbol[] varProduction in productions[var])
{
if (Program.debug)
Console.WriteLine("CFG: LL(1) table gen, var = " + var + " prod = " + SymbolsToString(varProduction));
ISet<Terminal> productionFirst = First(varProduction);
// add an entry to the parse table for each terminal in the first set of the production
foreach (Terminal term in productionFirst)
{
if (term != Terminal.EPSILON)
{
if (parseTable.Get(var, term) != null) // LL(1) violation
{
if (Program.debug)
{
Console.WriteLine("CFG: LL(1) violation at (First) [" + var + "," + term + "]");
Console.WriteLine("\tWas: " + SymbolsToString(parseTable.Get(var, term)));
Console.WriteLine("\tNew: " + SymbolsToString(varProduction));
}
return null;
}
else
{
parseTable.Add(var, term, varProduction);
}
}
}
// if epsilon can be derived from the production
// add an entry to the parse table for each terminal in the follow set of the nonterminal as well
if (productionFirst.Contains(Terminal.EPSILON))
{
foreach (Terminal term in Follow(var))
{
if (parseTable.Get(var, term) != null) // LL(1) violation
{
if (Program.debug)
{
Console.WriteLine("CFG: LL(1) violation at (Follow) [" + var + "," + term + "]");
Console.WriteLine("\tWas: " + SymbolsToString(parseTable.Get(var, term)));
Console.WriteLine("\tNew: " + SymbolsToString(varProduction));
}
return null;
}
else
{
parseTable.Add(var, term, varProduction);
}
}
}
}
}
if (Program.debug)
foreach (Nonterminal var in nonterminals)
foreach (Terminal term in terminals)
if (parseTable.Get(var, term) != null)
Console.WriteLine("CFG: LL(1) Table[" + var + "][" + term + "] = " + SymbolsToString(parseTable.Get(var, term)));
return parseTable;
}
// Builds an LL(1) parse table using the First and Follow sets for the grammar
// returns null if CFG is not LL(1)
public ParseTable CreateLL1ParseTable()
{
ComputeFirstSets();
ComputeFollowSets();
if (Program.debug)
{
Console.WriteLine("=========================================================");
}
ParseTable parseTable = new ParseTable();
// for each nonterminal in the grammar and each production rule for the nonterminal
foreach (Nonterminal var in productions.Keys)
{
foreach (ISymbol[] varProduction in productions[var])
{
if (Program.debug)
{
Console.WriteLine("CFG: LL(1) table gen, var = " + var + " prod = " + SymbolsToString(varProduction));
}
ISet <Terminal> productionFirst = First(varProduction);
// add an entry to the parse table for each terminal in the first set of the production
foreach (Terminal term in productionFirst)
{
if (term != Terminal.EPSILON)
{
if (parseTable.Get(var, term) != null) // LL(1) violation
{
if (Program.debug)
{
Console.WriteLine("CFG: LL(1) violation at (First) [" + var + "," + term + "]");
Console.WriteLine("\tWas: " + SymbolsToString(parseTable.Get(var, term)));
Console.WriteLine("\tNew: " + SymbolsToString(varProduction));
}
return(null);
}
else
{
parseTable.Add(var, term, varProduction);
}
}
}
// if epsilon can be derived from the production
// add an entry to the parse table for each terminal in the follow set of the nonterminal as well
if (productionFirst.Contains(Terminal.EPSILON))
{
foreach (Terminal term in Follow(var))
{
if (parseTable.Get(var, term) != null) // LL(1) violation
{
if (Program.debug)
{
Console.WriteLine("CFG: LL(1) violation at (Follow) [" + var + "," + term + "]");
Console.WriteLine("\tWas: " + SymbolsToString(parseTable.Get(var, term)));
Console.WriteLine("\tNew: " + SymbolsToString(varProduction));
}
return(null);
}
else
{
parseTable.Add(var, term, varProduction);
}
}
}
}
}
if (Program.debug)
{
foreach (Nonterminal var in nonterminals)
{
foreach (Terminal term in terminals)
{
if (parseTable.Get(var, term) != null)
{
Console.WriteLine("CFG: LL(1) Table[" + var + "][" + term + "] = " + SymbolsToString(parseTable.Get(var, term)));
}
}
}
}
return(parseTable);
}
