public void ExecuteReduces(GlrStep step, GlrStackItem stackTop) {
var inputTerm = step.Input.Term;
GlrParserAction actionInfo;
if (!stackTop.State.GlrActions.TryGetValue(inputTerm, out actionInfo)) {
step.Discarded.Add(stackTop);
return;
}
// if this top is elligible for shift on input, add it to step.ShiftBases
if (actionInfo.Shifts.Count > 0)
step.ShiftBases.Add(stackTop);
foreach (var reduceItem in actionInfo.Reduces) {
if (!reduceItem.Lookaheads.Contains(inputTerm)) continue;
//execute reduce
var prod = reduceItem.Core.Production;
var prodLen = prod.RValues.Count;
var sliceBuffer = new GlrStackSlice(prodLen);
foreach (var slice in EnumerateTopStackSlices(stackTop, sliceBuffer)) {
// the slice contains top stack elements, we can now try to reduce
var newNode = prod.ExecuteReduce(slice.Items.Select(el => el.ParseNode));
//Shift over newNode from all stack elements preceding reduced segment
foreach (var prev in sliceBuffer.PrecedingItems) {
GlrParserAction actionFromPrev;
if (!prev.State.GlrActions.TryGetValue(newNode.Term, out actionFromPrev) || actionFromPrev.Shifts.Count == 0)
// TODO: possible it never happens in LALR, investigate!
continue; // no shifts over newNode;
// find next state after shifting node
var stateAfterShift = actionFromPrev.Shifts[0].ShiftedItem.State;
// do not check here if this state is compatible with input; if not it will be discarded inside the ExeduceReduces call that follows
var itemAfterShift = new GlrStackItem(stateAfterShift, newNode, prev);
ExecuteReduces(step, itemAfterShift);
}// foreach prev
}//foreach path
}//foreach reduce
}//method
}//method
public void ExecuteShift(GlrStep step) {
//execute shifts on ShiftBases over input. Merge stack elements with the same state - see merging suffixes in Parsing Techniques
foreach (var shiftFrom in step.ShiftBases) {
GlrParserAction action;
if (!shiftFrom.State.GlrActions.TryGetValue(step.Input.Term, out action)) continue;
// if (action.Shifts.Count == 0) continue; // that never happens, step.ShiftBases has only items that have shifts over input
var nextState = action.Shifts[0].ShiftedItem.State;
GlrStackItem nextItem;
if (step.Shifts.TryGetValue(nextState, out nextItem))
nextItem.Previous.Add(shiftFrom); //add back link to existing stack elem with the same state
else
// create new stack element
step.Shifts[nextState] = new GlrStackItem(nextState, step.Input, shiftFrom);
}
}
