public static IEnumerable <Stack <Token> > ReductionOptions(this IEnumerable <Token> proposedStack)
{
var stack = proposedStack.ToArray();
for (var j = 1; j <= stack.Length && j <= 4; j++)
{
var head = stack.Subarray(0, j);
var tail = stack.Subarray(j, stack.Length - j);
if (Sentence.Propose(head))
{
var possibleStack = new List <Token>();
possibleStack.Add(new Sentence(head));
possibleStack.AddRange(tail);
yield return(possibleStack.ToStack());
}
if (VerbPhrase.Propose(head))
{
var possibleStack = new List <Token>();
possibleStack.Add(new VerbPhrase(head));
possibleStack.AddRange(tail);
yield return(possibleStack.ToStack());
}
if (NounPhrase.Propose(head))
{
var possibleStack = new List <Token>();
possibleStack.Add(new NounPhrase(head));
possibleStack.AddRange(tail);
yield return(possibleStack.ToStack());
}
}
}
