//
// Context-Free languages, CFG and LR Parsing
//
/// <summary>
/// G3 in "A Survey of LR-Parsing Methods", Gallier.
/// </summary>
public static void GallierLookaheadLR_Example3()
{
var grammar = DragonBookExample4_48.GetGrammar();
// characteristic automaton (LR(0) automaton)
var dfaLr0 = grammar.GetLr0AutomatonDfa();
SaveFile("GallierEx3_LR0Automaton.dot", DotLanguagePrinter.ToDotLanguage(dfaLr0, DotRankDirection.LeftRight, skipStateLabeling: true));
var analyzer = Analyzers.CreateErasableSymbolsAnalyzer(grammar);
//(ImmutableArray<IReadOnlySet<Terminal>> initfirstSets, IGraph graphFirst) = DigraphAlgorithm.GetFirstGraph(grammar, analyzer);
(var initfirstSets, IGraph graphFirst) = DigraphAlgorithm.GetFirstGraph(grammar, analyzer);
SaveFile("GallierEx3_FirstGraph.dot",
DigraphDotLanguagePrinter.PrintGraph("INITFIRST", initfirstSets, graphFirst, v => grammar.Nonterminals[v].Name));
var firstSymbolsAnalyzer = Analyzers.CreateFirstSymbolsAnalyzer(grammar);
(var initFollowSets, IGraph graphFollow) = DigraphAlgorithm.GetFollowGraph(grammar, firstSymbolsAnalyzer);
SaveFile("GallierEx3_FollowGraph.dot",
DigraphDotLanguagePrinter.PrintGraph("INITFOLLOW", initFollowSets, graphFollow, v => grammar.Nonterminals[v].Name));
var stringWriter = new StringWriter();
grammar.PrintFirstAndFollowSets(stringWriter);
SaveFile("GallierEx3_FirstAndFollowSets.txt", stringWriter.ToString());
// Grammar is LR(0)
var lr0Parser = grammar.ComputeLr0ParsingTable();
var writer = new StringWriter();
lr0Parser.PrintParsingTable(writer);
foreach (var conflict in lr0Parser.Conflicts)
{
writer.WriteLine(conflict);
writer.WriteLine($"In state {conflict.State}: {lr0Parser.GetItems(conflict.State).KernelItems.ToVectorString()} (kernel items)");
}
writer.WriteLine();
SaveFile("GallierEx3_Lr0ParsingTable.txt", writer.ToString());
////
var vertices = LalrLookaheadSetsAlgorithm.GetGotoTransitionPairs(grammar, dfaLr0);
// Read (INITFOLLOW) sets
var(directReads, graphRead) = LalrLookaheadSetsAlgorithm.GetGraphReads(grammar, dfaLr0, vertices, analyzer);
SaveFile("GallierEx3_ReadGraph.dot",
DigraphDotLanguagePrinter.PrintGraph("DR", directReads, graphRead, v => vertices[v].ToString()));
var graphLaFollow = LalrLookaheadSetsAlgorithm.GetGraphLaFollow(grammar, dfaLr0, vertices, analyzer);
SaveFile("GallierEx3_LaFollowGraph.dot",
DigraphDotLanguagePrinter.PrintGraph("INITFOLLOW", directReads, graphLaFollow, v => vertices[v].ToString()));
}
public static void DigraphMethods()
{
var grammar = GallierCalc.GetGrammar();
var analyzer = Analyzers.CreateErasableSymbolsAnalyzer(grammar);
(var initfirstSets, IGraph graphFirst) = DigraphAlgorithm.GetFirstGraph(grammar, analyzer);
SaveFile("FirstGraph.dot", DigraphDotLanguagePrinter.PrintGraph("INITFIRST", initfirstSets, graphFirst, v => grammar.Nonterminals[v].Name));
var firstSymbolsAnalyzer = Analyzers.CreateFirstSymbolsAnalyzer(grammar);
(var initFollowSets, IGraph graphFollow) = DigraphAlgorithm.GetFollowGraph(grammar, firstSymbolsAnalyzer);
SaveFile("FollowGraph.dot", DigraphDotLanguagePrinter.PrintGraph("INITFOLLOW", initFollowSets, graphFollow, v => grammar.Nonterminals[v].Name));
}
public void GetFollowGraph()
{
var analyzer = Analyzers.CreateFirstSymbolsAnalyzer(Grammar);
var(initSets, graph) = DigraphAlgorithm.GetFollowGraph(Grammar, analyzer);
// INITFOLLOW(S)
initSets[0].ShouldBeEmpty();
// INITFOLLOW(E)
initSets[1].ShouldSetEqual(Grammar.Ts(Sym.PLUS, Sym.RPARAN, Sym.EOF));
// INITFOLLOW(T)
initSets[2].ShouldSetEqual(Grammar.Ts(Sym.ASTERISK));
// INITFOLLOW(F)
initSets[3].ShouldBeEmpty();
var closureSets = DigraphAlgorithm.Traverse(graph, new[]
{
// trick to inspect closure (unions)
new Set <string> {
"S"
},
new Set <string> {
"E"
},
new Set <string> {
"T"
},
new Set <string> {
"F"
}
});
// FOLLOW(S) = INITFOLLOW(S)
closureSets[0].ShouldSetEqual("S");
// FOLLOW(E) = INITFOLLOW(S) ∪ INITFOLLOW(E)
closureSets[1].ShouldSetEqual("S", "E");
// FOLLOW(T) = INITFOLLOW(S) ∪ INITFOLLOW(E) ∪ INITFOLLOW(T) ∪ INITFOLLOW(F)
closureSets[2].ShouldSetEqual("S", "E", "T", "F");
// FOLLOW(F) = INITFOLLOW(S) ∪ INITFOLLOW(E) ∪ INITFOLLOW(T) ∪ INITFOLLOW(F)
closureSets[3].ShouldSetEqual("S", "E", "T", "F");
}