/// <summary>
/// Attempts to return a direct link to the specified parent.
/// </summary>
/// <param name="parent">The parent to look for.</param>
/// <returns>The <see cref="Link"/> to the specified parent;
/// or <see langword="null"/> when the specified frame is no parent
/// of this frame.</returns>
public Link TryGetParentLink(Frame parent)
{
#region Contract
Contract.Requires<ArgumentNullException>(parent != null);
#endregion
return this.Links.FirstOrDefault(l => l.Parent == parent);
}
/// <summary>
/// Initializes a new instance of the <see cref="ActionState"/> class.
/// </summary>
/// <param name="stack"></param>
/// <param name="state"></param>
/// <param name="currentToken"></param>
public ActionState(Frame stack, StateRef state, CodePoint currentToken)
: this()
{
#region Contract
Contract.Requires<ArgumentNullException>(stack != null);
#endregion
this.Stack = stack;
this.NextState = state;
this.CurrentToken = currentToken;
}
/// <summary>
/// Initializes a new instance of the <see cref="Link"/> class.
/// </summary>
/// <param name="parent">The parent/destination frame.</param>
/// <param name="label">The label of this link.</param>
/// <param name="length"></param>
public Link(Frame parent, IParseNode label, int length)
{
#region Contract
Contract.Requires<ArgumentNullException>(parent != null);
Contract.Requires<ArgumentNullException>(label != null);
Contract.Requires<ArgumentOutOfRangeException>(length >= 0);
#endregion
this.Parent = parent;
this.Label = label;
this.IsRejected = false;
this.Length = length;
}
/// <summary>
/// Initializes a new instance of the <see cref="Path"/> class.
/// </summary>
/// <param name="next">The next node in the path; or <see langword="null"/>.</param>
/// <param name="link">The associated link; or <see langword="null"/>.</param>
/// <param name="frame">The associated stack frame.</param>
/// <param name="length"></param>
public Path(Path next, Link link, Frame frame, int length)
{
#region Contract
Contract.Requires<ArgumentNullException>(frame != null);
Contract.Requires<ArgumentOutOfRangeException>(length >= 0);
#endregion
this.Next = next;
this.Link = link;
this.Frame = frame;
this.Length = length;
this.AncestorCount = next != null ? next.AncestorCount + 1 : 0;
this.label = this.Link?.Label;
}
/// <summary>
/// Gets an active stack frame with the specified state,
/// or creates and adds one if there is none.
/// </summary>
/// <param name="state">The state to look for.</param>
/// <returns>A <see cref="Frame"/> with the specified state.</returns>
private Frame GetOrCreateActiveFrame(StateRef state)
{
#region Contract
Contract.Ensures(Contract.Result<Frame>() != null);
Contract.Ensures(Contract.Result<Frame>().State == state);
#endregion
var frame = GetActiveFrame(state);
if (frame == null)
{
frame = new Frame(state);
this.activeStacks.PushFront(frame);
}
return frame;
}
/// <summary>
/// Checks whether the production is a completion production, and if so, checks
/// the boundaries for the completion region, the parser location and the cursor
/// location, and whether the parser is in completion mode.
/// Otherwise, when the production is not a completion production,
/// checks whether it is a recover production, or the parser is in fine grained recovery mode.
/// </summary>
/// <param name="stack"></param>
/// <param name="production"></param>
/// <returns></returns>
private bool RecoverModeOk(Frame stack, ProductionRule production)
{
if (!production.IsCompletion)
return !production.IsRecover || isFineGrainedMode; // TODO: isFineGrainedMode
return InCompletionMode(production);
}
/// <param name="st0"></param>
/// <param name="nextState"></param>
/// <param name="label"></param>
/// <param name="kids">A list of trees.</param>
/// <param name="path"></param>
private void Reducer(Frame st0, StateRef nextState, LabelRef label, IReadOnlyList<IParseNode> kids, Path path)
{
var production = this.parseTable.Labels[label.Index].Production;
Contract.Assert(!production.IsRecover);
// t := application of a -> A to kids
IParseNode t = ApplyProduction(production, kids, /* TODO */ 0, /* TODO */ 0, /* TODO */ false, /* TODO */ false);
Frame st1 = GetActiveFrame(nextState);
if (st1 != null)
{
// A stack with state nextState exists. Check for ambiguities.
Link nl = st1.TryGetParentLink(st0);
if (nl != null)
{
// There exists a direct link from st1 to st0.
// TODO: Add `t` to the possiblities of the ambiguity node at `tree(nl)`
if (production.IsReject)
nl.Reject();
// TODO: Can't modify a link.
//nl.Label = t;
}
else
{
// There is no direct link from st1 to st0.
nl = new Link(st0, t, path.Length);
st1.Links.Add(nl);
if (production.IsReject)
nl.Reject();
ActorOnActiveStacksOverNewLink(nl);
}
}
else
{
// Found no existing stack frame with state nextState.
st1 = new Frame(nextState);
this.activeStacks.PushFront(st1);
this.forActorDelayed.PushFront(st1);
var nl = new Link(st0, t, path.Length);
st1.Links.Add(nl);
if (production.IsReject)
nl.Reject();
}
}
// TODO: Rename to DoReductions?
/// <summary>
///
/// </summary>
/// <param name="stack"></param>
/// <param name="label"></param>
/// <param name="link">; or <see langword="null"/>.</param>
public void DoLimitedReductions(Frame stack, LabelRef label, Link link)
{
#region Contract
Contract.Requires<ArgumentNullException>(stack != null);
Contract.Requires<ArgumentNullException>(label != null);
#endregion
var production = this.parseTable.Labels[label.Index].Production;
if (!RecoverModeOk(stack, production))
return;
var paths = stack.FindPathsToRoot(production.Arity, link);
ReduceAllPaths(label, paths);
}
/// <summary>
/// Reduces the specified stack frame
/// </summary>
/// <param name="stack"></param>
/// <param name="label"></param>
public void DoReductions(Frame stack, LabelRef label)
{
DoLimitedReductions(stack, label, null);
}
// TODO: Can currentToken be removed?
/// <summary>
/// Enqueues the specified stack frame and next state for the shifter.
/// </summary>
/// <param name="stack">The current stack frame.</param>
/// <param name="nextState">The next state.</param>
/// <param name="currentToken">The current token.</param>
public void EnqueueForShifter(Frame stack, StateRef nextState, CodePoint currentToken)
{
#region Contract
Contract.Requires<ArgumentNullException>(stack != null);
Contract.Requires<ArgumentNullException>(nextState != null);
#endregion
this.forShifter.PushFront(new ActionState(stack, nextState, currentToken));
}
/// <summary>
/// Attempts to accept the specified stack frame.
/// </summary>
/// <param name="stack">The stack frame to accept.</param>
/// <returns><see langword="true"/> when the stack frame was accepted;
/// otherwise, <see langword="false"/>.</returns>
public bool TryAccept(Frame stack)
{
#region Contract
Contract.Requires<ArgumentNullException>(stack != null);
#endregion
if (stack.IsRejected)
return false;
this.AcceptingStack = stack;
SglrEngine.trace.TraceInformation($"Accepted stack {stack}.");
return true;
}
/// <summary>
/// Executes all actions associated with the current state of the stack frame,
/// if the action accepts the current token.
/// </summary>
/// <param name="frame">The stack frame.</param>
private void ExecuteActions(Frame frame)
{
SglrEngine.trace.TraceInformation("Executing actions for frame {0}.", frame);
var state = GetState(frame.State);
foreach (var action in state.Actions)
{
if (!action.Accepts(this.CurrentToken))
continue;
foreach (var actionItem in action.Items)
{
actionItem.Execute(this, frame);
}
}
}
