private void Initialize()
{
// for all (S ::= α) ∈ P {
foreach (var production in _grammar.ProductionsFrom(_grammar.Start))
{
var α0 = production.Rhs.FirstOrDefault();
var potentialItem = new EarleyItem(new DecoratedProduction(production, 0), 0, null);
// if α ∈ Σ_N, add (S ::= · α, 0, null) to E_0
if (PrefixInSigma(α0))
{
_E[0].Add(potentialItem);
}
// if α = a_0 α′, add (S ::= · α, 0, null) to Q′
else
{
if (_a.Count > 0)
{
var a1 = _a.First();
if (α0 == a1)
{
_QPrime.Add(potentialItem);
}
}
}
}
}
private void ProcessQ(int i)
{
if (i < _a.Count)
{
// create an SPPF node v labelled(a_i, i, i + 1)
var v2 = new SppfWord(_a[i], i, i + 1);
// while Q ̸= ∅ {
while (!_Q.IsEmpty)
{
// remove an element, Λ = (B ::= α · a_i β, h, w) say, from Q
var Λ = _Q.TakeOne();
if (Λ.DecoratedProduction.NextWord != _a[i])
{
throw new Exception();
// continue;
}
var h = Λ.StartPosition;
var w = Λ.SppfNode;
var β0 = Λ.DecoratedProduction.TailFirst;
// let y = MAKE NODE(B ::= α a_i · β, h, i + 1, w, v, V)
var productionAdvanced = Λ.DecoratedProduction.Increment();
var y = MakeNode(productionAdvanced, h, i + 1, w, v2);
var newItem = new EarleyItem(productionAdvanced, h, y);
// if β ∈ Σ_N { add (B ::= α a_i · β, h, y) to E_i+1 }
if (PrefixInSigma(β0))
{
_E[i + 1].Add(newItem);
}
// if β = a_i+1 β′ { add (B ::= α a_i · β, h, y) to Q′ }
else
{
if (i + 1 < _a.Count)
{
var aNext = _a[i + 1];
if (β0 == aNext)
{
_QPrime.Add(newItem);
}
}
}
}
}
}
private bool GatherExcludes(EarleyItem parent, EarleyItem child)
{
var parentProduction = parent.DecoratedProduction.Production;
var parentGathers = parentProduction.Annotations.Gather;
if (parentGathers == null)
{
return(false);
}
var parentPrecedence = parentProduction.Annotations.Precedence;
if (parentPrecedence == null)
{
return(false);
}
var childPrecedence = child.DecoratedProduction.Production.Annotations.Precedence;
if (childPrecedence == null)
{
return(false);
}
// S + * S [* is at 2]
//var subSentence = parent.DecoratedProduction.Production.Rhs.Take(parent.DecoratedProduction.CurrentPosition);
//var numNonterminals = subSentence.Count(word => word.IsNonterminal);
var numNonterminals = parentProduction.NumNonterminalsBefore(parent.DecoratedProduction.CurrentPosition);
var parentGather = parentGathers.Value[numNonterminals];
switch (parentGather)
{
case GatherOption.SameOrLower:
if (childPrecedence.Value > parentPrecedence.Value)
{
return(true);
}
break;
case GatherOption.StrictlyLower:
if (childPrecedence.Value >= parentPrecedence.Value)
{
return(true);
}
break;
}
return(false);
}
private void LinkCompletedChildWithParent(int i, EarleyItem parent, EarleyItem child, EarleySet R, SppfNode w)
{
var k = parent.StartPosition;
var z = parent.SppfNode;
// var δ = item.Tail;
var δ0 = parent.DecoratedProduction.TailFirst;
// Λ is child, item is parent
var gatherExcludes = GatherExcludes(parent, child);
if (gatherExcludes)
{
return;
}
// let y = MAKE NODE(A ::= τD · δ, k, i, z, w, V)
var productionAdvanced = parent.DecoratedProduction.Increment();
var y = MakeNode(productionAdvanced, k, i, z, w);
var newItem = new EarleyItem(productionAdvanced, k, y);
// if δ ∈ Σ_N and (A ::= τD · δ, k, y) ̸∈ E_i {
if (PrefixInSigma(δ0))
{
// add (A ::= τD · δ, k, y) to E_i and R
if (_E[i].Add(newItem))
{
R.Add(newItem);
}
}
else
{
// if δ = a_i δ′ { add (A ::= τD · δ, k, y) to Q } }
if (i < _a.Count)
{
var aCurr = _a[i];
if (δ0 == aCurr)
{
_Q.Add(newItem);
}
}
}
}
// if Λ = (D ::= α·, h, w) {
private void Complete(int i, Dictionary <Nonterminal, SppfNode> H, EarleySet R, EarleyItem Λ)
{
var D = Λ.DecoratedProduction.Production.Lhs;
var w = Λ.SppfNode;
var h = Λ.StartPosition;
// if w = null {
if (w == null)
{
// if there is no node v ∈ V labelled (D, i, i) create one
var v = _V.GetOrSet(D, i, i);
// set w = v
w = v;
Λ.SppfNode = v;
// if w does not have family (ϵ) add one
w.AddFamily(Λ.DecoratedProduction.Production, new SppfEpsilon(i, i));
}
// if h = i { add (D, w) to H }
if (h == i)
{
if (H.TryGetValue(D, out var oldw))
{
if (w != oldw)
{
throw new Exception("Different D, w in H");
}
}
else
{
H[D] = w;
}
}
var eh = _E[h];
// for all (A ::= τ · Dδ, k, z) in E_h {
//var count = eh.Count; // TODO: notice this doesn't run on items added to eh during the loop, not sure if this is right
//for (var itemi = 0; itemi < count; itemi++) {
// var item = eh[itemi];
// if (item.DecoratedProduction.NextWord != D) {
// continue;
// }
// LinkCompletedChildWithParent(V, i, item, Λ, R, Q, w);
//}
var list = eh.ItemsAtNonterminal(D);
if (list == null)
{
return;
}
var count = list.Count;
for (var listi = 0; listi < count; listi++)
{
var item = list[listi];
LinkCompletedChildWithParent(i, item, Λ, R, w);
}
}
// if Λ = (B ::= α · Cβ, h, w) {
private void Predict(int i, Dictionary <Nonterminal, SppfNode> H, EarleySet R, EarleyItem Λ, Nonterminal C)
{
//var β = Λ.Tail;
var w = Λ.SppfNode;
var h = Λ.StartPosition;
var β0 = Λ.DecoratedProduction.TailFirst;
// for all (C ::= δ) ∈ P {
foreach (var production in _grammar.ProductionsFrom(C))
{
// if δ ∈ Σ_N and (C ::= ·δ, i, null) ̸∈ E_i {
var δ0 = production.Rhs.FirstOrDefault();
var newItem = new EarleyItem(new DecoratedProduction(production, 0), i, null);
if (PrefixInSigma(δ0))
{
// add (C ::= ·δ, i, null) to E_i and R }
if (_E[i].Add(newItem))
{
R.Add(newItem);
}
}
else
{
// if δ = a_i δ′ { add (C ::= · δ, i, null) to Q }
if (i < _a.Count)
{
var aCurr = _a[i];
if (δ0 == aCurr)
{
_Q.Add(newItem);
}
}
}
}
// if ((C, v) ∈ H) {
if (H.TryGetValue(C, out SppfNode v))
{
// let y = MAKE_NODE(B ::= αC · β, h, i, w, v, V)
var productionAdvanced = Λ.DecoratedProduction.Increment();
var y = MakeNode(productionAdvanced, h, i, w, v);
var newItem = new EarleyItem(productionAdvanced, h, y);
// if β ∈ Σ N and (B ::= αC · β, h, y) ̸∈ E_i {
if (PrefixInSigma(β0))
{
// add(B::= αC · β, h, y) to E_i and R }
if (_E[i].Add(newItem))
{
R.Add(newItem);
}
}
else
{
// if β = a_i β′ { add (B ::= αC · β, h, y) to Q } } }
if (i < _a.Count)
{
var aCurr = _a[i];
if (β0 == aCurr)
{
_Q.Add(newItem);
}
}
}
}
}