|
static private GetNullable ( ISet |
||
| originalProductions | ISet |
|
| return | double>.Dictionary | |
/// <summary>
/// Eliminate ε-rules
/// </summary>
/// <param name="productions"></param>
// TODO: Does not preserve weights
private void StepDel(ISet <Production> productions)
{
var nullableProbabilities = GrammarHelpers.GetNullable(productions);
var newRules = new List <Production>();
foreach (var production in productions)
{
var toAdd = Nullate(production, nullableProbabilities);
RemoveExtraneousNulls(toAdd);
newRules.AddRange(toAdd);
}
productions.Clear();
productions.UnionWith(newRules);
}
protected void BuildHelpers()
{
_weightTotalsByNonterminal = Cache.Create(() => Helpers.BuildLookup(
() => this.Productions,
(p) => p.Lhs,
(p) => p.Weight,
() => new Boxed <double>(0.0),
(x, y) => x.Value += y
));
this.Caches.Add(_weightTotalsByNonterminal);
_nonterminals = Cache.Create(() => {
var hs = new HashSet <Nonterminal>();
hs.Add(Start);
foreach (var production in this.Productions)
{
hs.Add(production.Lhs);
foreach (var word in production.Rhs)
{
var nonterminal = word as Nonterminal;
if (nonterminal != null)
{
hs.Add(nonterminal);
}
}
}
return((ISet <Nonterminal>)hs);
});
this.Caches.Add(_nonterminals);
_terminals = Cache.Create(() => {
var hs = new HashSet <Terminal>();
foreach (var production in this.Productions)
{
foreach (var word in production.Rhs)
{
var terminal = word as Terminal;
if (terminal != null)
{
hs.Add(terminal);
}
}
}
return((ISet <Terminal>)hs);
});
this.Caches.Add(_terminals);
_nullableDict = Cache.Create(() => GrammarHelpers.GetNullable(new HashSet <Production>(Productions)));
this.Caches.Add(_nullableDict);
}
