private ImmutableList <Product> ExecuteNestedPipeline(ImmutableList <FactReference> startReferences, Pipeline pipeline, Projection projection)
{
var subset = Subset.FromPipeline(pipeline);
var namedSpecifications = projection.GetNamedSpecifications();
var products = (
from startReference in startReferences
from product in ExecutePipeline(startReference, pipeline)
select product).ToImmutableList();
var collections =
from namedSpecification in namedSpecifications
let name = namedSpecification.name
let childPipeline = pipeline.Compose(namedSpecification.specification.Pipeline)
let childProducts = ExecuteNestedPipeline(startReferences, childPipeline, namedSpecification.specification.Projection)
select(name, childProducts);
var mergedProducts = collections
.Aggregate(products, (source, collection) => MergeProducts(subset, collection.name, collection.childProducts, source));
return(mergedProducts);
}
