public Lr0AutomatonDigraphAnalyzer(
Grammar <TTokenKind, TNonterminal> grammar,
LrItemsDfa <TTokenKind> dfaLr0,
IErasableSymbolsAnalyzer analyzer)
{
_lookaheadSets = ComputeLookaheadSets(grammar, dfaLr0, analyzer);
}
internal FollowSetsDigraphAnalyzer(
Grammar <TTokenKind, TNonterminal> grammar,
IErasableSymbolsAnalyzer nullableSymbolsAnalyzer,
IFirstSetsAnalyzer <TTokenKind> starterTokensAnalyzer)
{
var analyzer = new FirstSymbolsAnalyzer <TTokenKind>(nullableSymbolsAnalyzer, starterTokensAnalyzer);
_followMap = ComputeFollow(grammar, analyzer);
}
public FollowSymbolsAnalyzer(
IErasableSymbolsAnalyzer nullableSymbolsAnalyzer,
IFirstSetsAnalyzer <TTokenKind> starterTokensAnalyzer,
IFollowSetsAnalyzer <TTokenKind> followerTokensAnalyzer)
{
_nullableSymbolsAnalyzer = nullableSymbolsAnalyzer;
_starterTokensAnalyzer = starterTokensAnalyzer;
_followerTokensAnalyzer = followerTokensAnalyzer;
}
private Dictionary <Nonterminal, Set <Terminal <TTokenKind> > > ComputeFirst(
Grammar <TTokenKind, TNonterminal> grammar, IErasableSymbolsAnalyzer analyzer)
{
var(initFirstSets, graph) = DigraphAlgorithm.GetFirstGraph(grammar, analyzer);
var firstSets = DigraphAlgorithm.Traverse(graph, initFirstSets);
var firstMap = grammar.Nonterminals.ToDictionary(v => v, v => firstSets[v.Index]);
return(firstMap);
}
// Relational formulation:
// t ∈ LA(q, A → ω) iff (q, A → ω) lookback (p,A) includes* (p',B) reads* (r,C) directly-reads t
//
// (r,C) directly-reads t iff t ∈ DR(r,C)
private static Dictionary <(int, int), Set <Terminal <TTokenKind> > > ComputeLookaheadSets(
Grammar <TTokenKind, TNonterminal> grammar,
LrItemsDfa <TTokenKind> dfaLr0,
IErasableSymbolsAnalyzer analyzer)
{
var vertices = LalrLookaheadSetsAlgorithm.GetGotoTransitionPairs(grammar, dfaLr0);
var(directReads, graphRead) = LalrLookaheadSetsAlgorithm.GetGraphReads(grammar, dfaLr0, vertices, analyzer);
// Read(p,A) sets
Set <Terminal <TTokenKind> >[] readSets = DigraphAlgorithm.Traverse(graphRead, directReads);
var graphLaFollow = LalrLookaheadSetsAlgorithm.GetGraphLaFollow(grammar, dfaLr0, vertices, analyzer);
// Follow(p,A) sets
Set <Terminal <TTokenKind> >[] followSets = DigraphAlgorithm.Traverse(graphLaFollow, readSets);
// LA(q, A → ω) = ∪{ Follow(p,A) | (q, A → ω) lookback (p,A) }
var lookaheadSets = LalrLookaheadSetsAlgorithm.GetLaUnion(grammar, dfaLr0, vertices, followSets);
return(lookaheadSets);
}
public static bool Erasable(this IErasableSymbolsAnalyzer analyzer, IEnumerable <Symbol> symbols)
{
// Nullable(X) = Nullable(Y1) Λ ... Λ Nullable(Yn), for X → Y1 Y2...Yn
// Nullable(ε) = true
return(symbols.All(analyzer.Erasable)); // All (&&-Monoid) is true by default, because true is the unit
}
internal FirstSetsDigraphAnalyzer(Grammar <TTokenKind, TNonterminal> grammar, IErasableSymbolsAnalyzer analyzer)
{
_firstMap = ComputeFirst(grammar, analyzer);
}
