public static ISequence <TResult> CreateOperator <TSource, TResult>(
ISequence <TSource> source,
Func <IIterator <TSource>, Result <TResult>, CancellationToken, Task <bool> > moveNext
)
{
return(Create(context => Iterator.CreateOperator <TSource, TResult>(source.Start(context), moveNext)));
}
public static ISequence <T> Scan <T>(this ISequence <T> source, Func <T, T, T> accumulator)
{
return(Create(context =>
{
T current = default(T);
bool accumulate = false;
return Iterator.CreateOperator <T, T>(source.Start(context), async(iterator, result, cancel) =>
{
if (!await iterator.MoveNext(cancel).ConfigureAwait(false))
{
return false;
}
if (accumulate)
{
current = accumulator(current, iterator.Current);
}
else
{
current = iterator.Current;
accumulate = true;
}
result.Value = current;
return true;
});
}));
}
public static ISequence <TAccumulate> ScanAsync <TSource, TAccumulate>(this ISequence <TSource> source, TAccumulate seed, Func <TAccumulate, TSource, Task <TAccumulate> > accumulator)
{
return(Create(context =>
{
var current = seed;
return Iterator.CreateOperator <TSource, TAccumulate>(source.Start(context), async(iterator, result, cancel) =>
{
if (!await iterator.MoveNext(cancel).ConfigureAwait(false))
{
return false;
}
current = await accumulator(current, iterator.Current);
result.Value = current;
return true;
});
}));
}
public static ISequence <T> Skip <T>(this ISequence <T> source, int count)
{
return(Create(context =>
{
int skip = count;
return Iterator.CreateOperator <T, T>(source.Start(context), async(iterator, result, cancel) =>
{
while (await iterator.MoveNext(cancel).ConfigureAwait(false))
{
if (skip <= 0)
{
result.Value = iterator.Current;
return true;
}
--skip;
}
return false;
});
}));
}
public static ISequence <T> Take <T>(this ISequence <T> source, int count)
{
if (count < 0)
{
throw new ArgumentException("Count must be greater or equal than 0.", "count");
}
return(Create(context =>
{
int remaining = count;
return Iterator.CreateOperator <T, T>(source.Start(context), async(iterator, result, cancel) =>
{
if (remaining > 0 && await iterator.MoveNext(cancel).ConfigureAwait(false))
{
result.Value = iterator.Current;
--remaining;
return true;
}
iterator.Dispose();
return false;
});
}));
}
