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);
}
private static Dictionary <Nonterminal, Set <Terminal <TTokenKind> > > ComputeFollow(
Grammar <TTokenKind, TNonterminal> grammar,
IFirstSymbolsAnalyzer <TTokenKind> analyzer)
{
var(initFollowSets, graph) = DigraphAlgorithm.GetFollowGraph(grammar, analyzer);
var followSets = DigraphAlgorithm.Traverse(graph, initFollowSets);
var followMap = grammar.Nonterminals.ToDictionary(v => v, v => followSets[v.Index]);
return(followMap);
}
// 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);
}
