public static List Select <T>(this List list, Func <T, Object> transform) where T : Object
{
if (list is Null)
{
return(Null.Instance);
}
IDictionary <Pair, Pair> transformations = new Dictionary <Pair, Pair>();
Pair current = list as Pair;
Pair resultStart, resultCurrent;
resultStart = resultCurrent = new Pair(transform(current.Car as T));
while (current != null && !transformations.ContainsKey(current))
{
transformations.Add(current, resultCurrent);
current = current.Cdr as Pair;
if (current != null && !transformations.ContainsKey(current))
{
resultCurrent = resultCurrent.Append(transform(current.Car as T));
}
}
if (current != null)
{
resultCurrent.Cdr = transformations[current];
}
return(resultStart);
}
public void AppendTest()
{
Pair list = Pair.GetList(1, 4);
Pair result = Pair.Append(list, 9);
Assert.Equal(9, result.Next.Next.Value);
}
public static List Filter <T>(this List list, Func <T, bool> predicate) where T : Object
{
if (list is Null)
{
return(Null.Instance);
}
Pair current = list as Pair;
HashSet <Pair> visitedPairs = new HashSet <Pair>();
while (current != null && !predicate(current.Car as T) && visitedPairs.Add(current))
{
current = current.Cdr as Pair;
}
if (current == null || visitedPairs.Contains(current))
{
return(Null.Instance);
}
Pair resultStart, resultCurrent;
resultStart = resultCurrent = new Pair(current.Car);
Dictionary <Pair, Pair> successfulPairs = new Dictionary <Pair, Pair> {
{ current, resultStart },
};
current = current.Cdr as Pair;
while (current != null && visitedPairs.Add(current))
{
if (predicate(current.Car as T))
{
resultCurrent = resultCurrent.Append(current.Car);
successfulPairs.Add(current, resultCurrent);
}
current = current.Cdr as Pair;
}
if (current != null)
{
Pair startOfCycle = current;
while (!successfulPairs.ContainsKey(current))
{
current = current.Cdr as Pair;
if (current == startOfCycle)
{
break;
}
}
resultCurrent.Cdr = successfulPairs[current];
}
return(resultStart);
}
public override Object VisitPair([NotNull] KernelParser.PairContext context)
{
if (context.dot != null)
{
Object[] expressions = context.expression().Select(VisitExpression).ToArray();
Pair start, pair;
start = pair = new Pair(expressions[0]);
for (int i = 1; i < expressions.Length - 1; i++)
{
pair = pair.Append(expressions[i]);
}
pair.Cdr = expressions[expressions.Length - 1];
return(start);
}
return(new Pair(context.expression().Select(VisitExpression)));
}
