/// <summary>
/// Return a list of all next possible states, having followed any
/// applicable transitions, given the current state.
/// </summary>
private IEnumerable <PDARunState> FindNextStates(PDARunState state)
{
// Follow each possible transition available.
return(from transition in Transitions
where transition.MatchesConfiguration(state)
select ApplyTransition(transition, state));
}
public bool MatchesConfiguration(PDARunState state)
{
return(InputChar == state.Input[0] &&
OldState == state.State &&
((StackHead == '_' && state.Stack.Count() == 0) ||
(state.Stack.Count() > 0 && StackHead == state.Stack[0])));
}
/// <summary>
/// Applies the given transition, to the given run state.
/// </summary>
/// <returns>
/// An IEnumerable of the states resulting from applying the transition.
/// </returns>
private static PDARunState ApplyTransition(PDATransition transition,
PDARunState state)
{
var newState = transition.NewState;
var newStack = state.Stack;
var newInput = state.Input.Substring(1);
var newMatchedSoFar = state.MatchedSoFar + 1;
var isFailure = false;
// If we're not matching against the empty stack, try pop.
if (transition.StackHead != '_')
{
if (newStack.Length > 0)
{
newStack = newStack.Substring(1);
}
else
{
// Cannot pop from the stack, so bail out here.
isFailure = true;
}
}
else if (newStack != "")
{
// Catch illegal use of empty stack transition.
isFailure = true;
}
if (!isFailure)
{
newStack = transition.StackReplace + newStack;
}
var returnState = new PDARunState(newInput, newMatchedSoFar, newStack, newState);
// Check for end-of-input without empty stack - failure.
// We won't be able to empty the stack if there are fewer input
// chars than stack elems, so fail to prevent unnecessary work.
if (isFailure || newInput == "" && newStack.Length > 0 || newInput.Length < newStack.Length)
{
returnState.Failure = true;
}
return(returnState);
}
public bool MatchesConfiguration(PDARunState state)
{
return InputChar == state.Input[0] &&
OldState == state.State &&
((StackHead == '_' && state.Stack.Count() == 0) ||
(state.Stack.Count() > 0 && StackHead == state.Stack[0]));
}
/// <summary>
/// Return a list of all next possible states, having followed any
/// applicable transitions, given the current state.
/// </summary>
private IEnumerable<PDARunState> FindNextStates(PDARunState state)
{
// Follow each possible transition available.
return from transition in Transitions
where transition.MatchesConfiguration(state)
select ApplyTransition(transition, state);
}
/// <summary>
/// Applies the given transition, to the given run state.
/// </summary>
/// <returns>
/// An IEnumerable of the states resulting from applying the transition.
/// </returns>
private static PDARunState ApplyTransition(PDATransition transition,
PDARunState state)
{
var newState = transition.NewState;
var newStack = state.Stack;
var newInput = state.Input.Substring(1);
var newMatchedSoFar = state.MatchedSoFar + 1;
var isFailure = false;
// If we're not matching against the empty stack, try pop.
if (transition.StackHead != '_')
{
if (newStack.Length > 0)
{
newStack = newStack.Substring(1);
}
else
{
// Cannot pop from the stack, so bail out here.
isFailure = true;
}
}
else if (newStack != "")
{
// Catch illegal use of empty stack transition.
isFailure = true;
}
if (!isFailure)
{
newStack = transition.StackReplace + newStack;
}
var returnState = new PDARunState(newInput, newMatchedSoFar, newStack, newState);
// Check for end-of-input without empty stack - failure.
// We won't be able to empty the stack if there are fewer input
// chars than stack elems, so fail to prevent unnecessary work.
if (isFailure || newInput == "" && newStack.Length > 0 || newInput.Length < newStack.Length)
{
returnState.Failure = true;
}
return returnState;
}
