/*
* Initial condition: we have state S with conflicts on lookaheads in Sc.Conflicts.
* Each reduce item Ir in S has a set of lookahead sources Ir.ReducedLookaheadSources.
* Our goal is to a create non-canonical state ncState with proper lookaheds, create jumps to this state
* on jump lookaheads from S to ncState, remove these jump lookaheads from lookahead sets of reduce items
* and replace them with non-canonical non-terminal lookaheads.
* 1. Compute all jump lookaheads jL and non-canonical lookaheads ncL for state Sc.
* 2. Collect relevant lookahead sources in lkhSources set. For each lookahead source lkhSrc in all reduce items,
* if lkhSrc.Current.Firsts includes a jump lookahead in jL, include it into lkhSources.
* 3. Collect item cores for non-canonical state into ncCores. For each production Prod in productions
* of current non-terminal of all items in lkhSources, if Prod.Firsts contains a jump lookahead, then add initial LR0 item of Prod
* to ncCores.
* 4. Add to ncCores all shift items in state Sc that have Current term in jump lookaheads. We need to include
* such shift items from original state into non-canonical state to allow proper resolution of shift-reduce
* conflicts. We let shift items in current state "compete" with possible reductions to non-canonical lookaheads
* inside non-canonical state.
* 5. Create (or find existing) non-canonical state Sn from ncCores.
* 6. Assign lookbacks to items in ncState. For each item Src in lkhSources, for each production Prod
* in Src.Current.Productions, if Prod.DirectFirsts contains jump lookahead, then:
* find LR item I in Sn with I.Core == Prod.LR0Items[0]; do the following: I.Lookbacks.Add(Src.Transition).
* 7. For state S for each reduce item I adjust I.Lookaheads: remove jump lookaheads from I.Lookaheads,
* and add those non-canonical lookaheads that are in I.AllLookaheads
*/
//TODO: one thing to look at - see if all items in ncState should lead to reduce item in some state.
// There may be items (most likely top ones, expansions of original reduced lookahead) that never get
// to full reduce, because we switch back to canonical state on reduction of some "child" non-terminal and
// continue through canonical states from there.
// So we don't need to generate target transition states for these items (unreachable states).
// The main trouble is that unreachable state may introduce conflicts that in fact are never realized.
#endregion
private void SwitchStateToNLalrLookaheads(ParserState state)
{
//1. Compute minimal (most expanded) non-canonical lookaheads that resolve all conflicts
ComputeStateNonCanonicalLookaheads(state);
var stateData = state.BuilderData;
//2. Collect reduced lookahead sources and non-terminal lookaheads
var lkhSources = new LRItemSet();
var ntSet = new NonTerminalSet(); //All non-terminals in current positions of lkhSources
foreach (var reduceItem in stateData.ReduceItems)
{
foreach (var lkhSource in reduceItem.ReducedLookaheadSources)
{
var ntLkh = lkhSource.Core.Current as NonTerminal;
if (ntLkh == null)
{
continue;
}
if (!ntLkh.Firsts.Overlaps(stateData.JumpLookaheads))
{
continue;
}
lkhSources.Add(lkhSource);
ntSet.Add(ntLkh);
}
}
//2. Collect core set for non-canonical state
var ncCoreSet = new LR0ItemSet();
foreach (var ntLkh in ntSet)
{
foreach (var prod in ntLkh.Productions)
{
if (prod.Firsts.Overlaps(stateData.JumpLookaheads))
{
ncCoreSet.Add(prod.LR0Items[0]);
}
}
}
//4. Add shift items
foreach (var shiftItem in stateData.ShiftItems)
{
if (stateData.JumpLookaheads.Contains(shiftItem.Core.Current))
{
ncCoreSet.Add(shiftItem.Core);
}
}
//5. Find or create non-canonical state
var oldStateCount = Data.States.Count;
var ncState = FindOrCreateState(ncCoreSet, "SN"); //if not found, state is created and added to state list and state hash
bool ncStateIsNew = Data.States.Count > oldStateCount;
stateData.JumpTarget = ncState;
//6. Setup appropriate lookbacks in items in ncState;
// first set lookbacks for items originated from lookaheads of reduce items in original state.
foreach (var lkhSource in lkhSources)
{
var ntLkh = lkhSource.Core.Current as NonTerminal;
foreach (var prod in ntLkh.Productions)
{
if (prod.Firsts.Overlaps(stateData.JumpLookaheads))
{
var ncItem = ncState.BuilderData.AllItems.FindByCore(prod.LR0Items[0]);
ncItem.Lookbacks.Add(lkhSource.Transition);
} //if
}
} //foreach lkhSource
//Now items orginated from shift items in original state in step 4 above
// just copy lookbacks
foreach (var shiftItem in stateData.ShiftItems)
{
if (stateData.JumpLookaheads.Contains(shiftItem.Core.Current))
{
var ncItem = ncState.BuilderData.ShiftItems.FindByCore(shiftItem.Core);
shiftItem.ShiftedItem = ncItem;
ncItem.Lookbacks.UnionWith(shiftItem.Lookbacks);
if (ncItem.Transition != null)
{
ncItem.Transition.Include(shiftItem.Transition.Includes);
}
}
}
PropagateLookbacksAndTransitionsThruShifts(ncState);
//7. Adjust reduce items lookaheads in original state
foreach (var reduceItem in stateData.ReduceItems)
{
foreach (var jumpLkh in stateData.JumpLookaheads)
{
if (reduceItem.Lookaheads.Contains(jumpLkh))
{
reduceItem.Lookaheads.Remove(jumpLkh);
}
}
foreach (var ncLkh in stateData.NonCanonicalLookaheads)
{
if (reduceItem.AllLookaheads.Contains(ncLkh))
{
reduceItem.Lookaheads.Add(ncLkh);
}
}
}//foreach reduceItem
// 8. Create jump action to non-canonical state, remove shifts on jump lookaheads
state.JumpAction = ParserAction.CreateJump(ncState);
foreach (var jumpTerm in state.BuilderData.JumpLookaheads)
{
if (state.Actions.ContainsKey(jumpTerm))
{
state.Actions.Remove(jumpTerm);
}
}
//9. Complete generating states
state.BuilderData.Conflicts.ExceptWith(state.BuilderData.JumpLookaheads);
}//method