pub fn add_fields(pipeline: Pipeline, doc: Value) -> Pipeline
pub fn aggregate(collection: Collection) -> Pipeline
pub fn exec(pipeline: Pipeline) -> Result(List(Value), MongoError)
pub fn group(pipeline: Pipeline, doc: Value) -> Pipeline
pub fn limit(pipeline: Pipeline, count: Int) -> Pipeline
pub fn lookup(pipeline: Pipeline, from from: String, local_field local_field: String, foreign_field foreign_field: String, alias alias: String) -> Pipeline
pub fn match(pipeline: Pipeline, doc: Value) -> Pipeline
pub fn project(pipeline: Pipeline, doc: Value) -> Pipeline
pub fn skip(pipeline: Pipeline, count: Int) -> Pipeline
pub fn sort(pipeline: Pipeline, doc: Value) -> Pipeline