diff --git a/timely/src/dataflow/channels/pact.rs b/timely/src/dataflow/channels/pact.rs
index 96aaed605..4362a4113 100644
--- a/timely/src/dataflow/channels/pact.rs
+++ b/timely/src/dataflow/channels/pact.rs
@@ -7,18 +7,14 @@
 //! The only requirement of a pact is that it not alter the number of `D` records at each time `T`.
 //! The progress tracking logic assumes that this number is independent of the pact used.
 
-use std::{fmt::{self, Debug}, marker::PhantomData};
+use std::fmt::Debug;
 use std::rc::Rc;
 
 use crate::Accountable;
-use crate::container::{ContainerBuilder, DrainContainer, LengthPreservingContainerBuilder, SizableContainer, CapacityContainerBuilder, PushInto};
 use crate::communication::allocator::thread::{ThreadPusher, ThreadPuller};
 use crate::communication::{Push, Pull};
-use crate::dataflow::channels::pushers::Exchange as ExchangePusher;
-use crate::dataflow::channels::pushers::exchange::DrainContainerDistributor;
 use crate::dataflow::channels::Message;
-use crate::logging::{TimelyLogger as Logger, MessagesEvent};
-use crate::progress::Timestamp;
+use crate::logging::TimelyLogger as Logger;
 use crate::worker::AsWorker;
 
 /// A `ParallelizationContract` allocates paired `Push` and `Pull` implementors.
@@ -45,162 +41,234 @@ impl<T: 'static, C: Accountable + 'static> ParallelizationContract<T, C> for Pip
     }
 }
 
-/// An exchange between multiple observers by data
-pub struct ExchangeCore<CB, F> { hash_func: F, phantom: PhantomData<CB> }
-
-/// [ExchangeCore] specialized to vector-based containers.
-pub type Exchange<D, F> = ExchangeCore<CapacityContainerBuilder<Vec<D>>, F>;
-
-impl<CB, F> ExchangeCore<CB, F>
-where
-    CB: LengthPreservingContainerBuilder,
-    CB::Container: DrainContainer,
-    for<'a> F: FnMut(&<CB::Container as DrainContainer>::Item<'a>)->u64
-{
-    /// Allocates a new `Exchange` pact from a distribution function.
-    pub fn new_core(func: F) -> ExchangeCore<CB, F> {
-        ExchangeCore {
-            hash_func:  func,
-            phantom:    PhantomData,
+pub use exchange::{ExchangeCore, Exchange};
+mod exchange {
+
+    use std::{fmt::{self, Debug}, marker::PhantomData};
+    use std::rc::Rc;
+
+    use crate::container::{ContainerBuilder, DrainContainer, LengthPreservingContainerBuilder, SizableContainer, CapacityContainerBuilder, PushInto};
+    use crate::communication::{Push, Pull};
+    use crate::dataflow::channels::pushers::Exchange as ExchangePusher;
+    use crate::dataflow::channels::pushers::exchange::DrainContainerDistributor;
+    use crate::dataflow::channels::Message;
+    use crate::logging::TimelyLogger as Logger;
+    use crate::progress::Timestamp;
+    use crate::worker::AsWorker;
+
+    use super::{ParallelizationContract, LogPusher, LogPuller};
+
+    /// An exchange between multiple observers by data
+    pub struct ExchangeCore<CB, F> { hash_func: F, phantom: PhantomData<CB> }
+
+    /// [ExchangeCore] specialized to vector-based containers.
+    pub type Exchange<D, F> = ExchangeCore<CapacityContainerBuilder<Vec<D>>, F>;
+
+    impl<CB, F> ExchangeCore<CB, F>
+    where
+        CB: LengthPreservingContainerBuilder,
+        CB::Container: DrainContainer,
+        for<'a> F: FnMut(&<CB::Container as DrainContainer>::Item<'a>)->u64
+    {
+        /// Allocates a new `Exchange` pact from a distribution function.
+        pub fn new_core(func: F) -> ExchangeCore<CB, F> {
+            ExchangeCore {
+                hash_func:  func,
+                phantom:    PhantomData,
+            }
         }
     }
-}
 
-impl<C, F> ExchangeCore<CapacityContainerBuilder<C>, F>
-where
-    C: SizableContainer + DrainContainer,
-    for<'a> F: FnMut(&C::Item<'a>)->u64
-{
-    /// Allocates a new `Exchange` pact from a distribution function.
-    pub fn new(func: F) -> ExchangeCore<CapacityContainerBuilder<C>, F> {
-        ExchangeCore {
-            hash_func:  func,
-            phantom:    PhantomData,
+    impl<C, F> ExchangeCore<CapacityContainerBuilder<C>, F>
+    where
+        C: SizableContainer + DrainContainer,
+        for<'a> F: FnMut(&C::Item<'a>)->u64
+    {
+        /// Allocates a new `Exchange` pact from a distribution function.
+        pub fn new(func: F) -> ExchangeCore<CapacityContainerBuilder<C>, F> {
+            ExchangeCore {
+                hash_func:  func,
+                phantom:    PhantomData,
+            }
         }
     }
-}
 
-// Exchange uses a `Box<Pushable>` because it cannot know what type of pushable will return from the allocator.
-impl<T: Timestamp, CB, H> ParallelizationContract<T, CB::Container> for ExchangeCore<CB, H>
-where
-    CB: ContainerBuilder<Container: DrainContainer> + for<'a> PushInto<<CB::Container as DrainContainer>::Item<'a>>,
-    CB::Container: Send + crate::dataflow::channels::ContainerBytes,
-    for<'a> H: FnMut(&<CB::Container as DrainContainer>::Item<'a>) -> u64 + 'static,
-{
-    type Pusher = ExchangePusher<
-        T,
-        LogPusher<Box<dyn Push<Message<T, CB::Container>>>>,
-        DrainContainerDistributor<CB, H>
-    >;
-    type Puller = LogPuller<Box<dyn Pull<Message<T, CB::Container>>>>;
+    // Exchange uses a `Box<Pushable>` because it cannot know what type of pushable will return from the allocator.
+    impl<T: Timestamp, CB, H> ParallelizationContract<T, CB::Container> for ExchangeCore<CB, H>
+    where
+        CB: ContainerBuilder<Container: DrainContainer> + for<'a> PushInto<<CB::Container as DrainContainer>::Item<'a>>,
+        CB::Container: Send + crate::dataflow::channels::ContainerBytes,
+        for<'a> H: FnMut(&<CB::Container as DrainContainer>::Item<'a>) -> u64 + 'static,
+    {
+        type Pusher = ExchangePusher<
+            T,
+            LogPusher<Box<dyn Push<Message<T, CB::Container>>>>,
+            DrainContainerDistributor<CB, H>
+        >;
+        type Puller = LogPuller<Box<dyn Pull<Message<T, CB::Container>>>>;
 
-    fn connect<A: AsWorker>(self, allocator: &mut A, identifier: usize, address: Rc<[usize]>, logging: Option<Logger>) -> (Self::Pusher, Self::Puller) {
-        let (senders, receiver) = allocator.allocate::<Message<T, CB::Container>>(identifier, address);
-        let senders = senders.into_iter().enumerate().map(|(i,x)| LogPusher::new(x, allocator.index(), i, identifier, logging.clone())).collect::<Vec<_>>();
-        let distributor = DrainContainerDistributor::new(self.hash_func, allocator.peers());
-        (ExchangePusher::new(senders, distributor), LogPuller::new(receiver, allocator.index(), identifier, logging.clone()))
+        fn connect<A: AsWorker>(self, allocator: &mut A, identifier: usize, address: Rc<[usize]>, logging: Option<Logger>) -> (Self::Pusher, Self::Puller) {
+            let (senders, receiver) = allocator.allocate::<Message<T, CB::Container>>(identifier, address);
+            let senders = senders.into_iter().enumerate().map(|(i,x)| LogPusher::new(x, allocator.index(), i, identifier, logging.clone())).collect::<Vec<_>>();
+            let distributor = DrainContainerDistributor::new(self.hash_func, allocator.peers());
+            (ExchangePusher::new(senders, distributor), LogPuller::new(receiver, allocator.index(), identifier, logging.clone()))
+        }
     }
-}
 
-impl<C, F> Debug for ExchangeCore<C, F> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Exchange").finish()
+    impl<C, F> Debug for ExchangeCore<C, F> {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            f.debug_struct("Exchange").finish()
+        }
     }
 }
 
-/// Wraps a `Message<T,D>` pusher to provide a `Push<(T, Content<D>)>`.
-#[derive(Debug)]
-pub struct LogPusher<P> {
-    pusher: P,
-    channel: usize,
-    counter: usize,
-    source: usize,
-    target: usize,
-    logging: Option<Logger>,
-}
+pub use distributor::DistributorPact;
+/// Parallelization contract based on a `Distributor` implementation.
+mod distributor {
+
+    use std::rc::Rc;
+
+    use crate::Accountable;
+    use crate::communication::{Push, Pull};
+    use crate::dataflow::channels::pushers::{Exchange, exchange::Distributor};
+    use crate::dataflow::channels::{ContainerBytes, Message};
+    use crate::logging::TimelyLogger;
+    use crate::progress::Timestamp;
+    use crate::worker::AsWorker;
+
+    use super::{ParallelizationContract, LogPusher, LogPuller};
+
+    /// Intended to wrap a function from a `usize` to an `impl Distributor`.
+    ///
+    /// For a `D: Distributor<C>` and an appropriate builder `D::new(peers: usize)`,
+    /// a `DistributorPact(|peers| D::new(peers))` acts as a pact that will use `D`
+    /// and distribute containers of type `C`.
+    pub struct DistributorPact<B>(pub B);
 
-impl<P> LogPusher<P> {
-    /// Allocates a new pusher.
-    pub fn new(pusher: P, source: usize, target: usize, channel: usize, logging: Option<Logger>) -> Self {
-        LogPusher {
-            pusher,
-            channel,
-            counter: 0,
-            source,
-            target,
-            logging,
+    impl<T, B, C, D> ParallelizationContract<T, C> for DistributorPact<B>
+    where
+        T: Timestamp,
+        B: FnOnce(usize) -> D,
+        C: Accountable + ContainerBytes + Send + 'static,
+        D: Distributor<C> + 'static,
+    {
+        type Pusher = Exchange<
+            T,
+            LogPusher<Box<dyn Push<Message<T, C>>>>,
+            D
+        >;
+        type Puller = LogPuller<Box<dyn Pull<Message<T, C>>>>;
+        fn connect<A: AsWorker>(self, allocator: &mut A, identifier: usize, address: Rc<[usize]>, logging: Option<TimelyLogger>) -> (Self::Pusher, Self::Puller) {
+            let (senders, receiver) = allocator.allocate::<Message<T, C>>(identifier, address);
+            let senders = senders.into_iter().enumerate().map(|(i,x)| LogPusher::new(x, allocator.index(), i, identifier, logging.clone())).collect::<Vec<_>>();
+            let distributor = (self.0)(allocator.peers());
+            (Exchange::new(senders, distributor), LogPuller::new(receiver, allocator.index(), identifier, logging.clone()))
         }
     }
 }
 
-impl<T, C: Accountable, P: Push<Message<T, C>>> Push<Message<T, C>> for LogPusher<P> {
-    #[inline]
-    fn push(&mut self, pair: &mut Option<Message<T, C>>) {
-        if let Some(bundle) = pair {
-            self.counter += 1;
-
-            // Stamp the sequence number and source.
-            // FIXME: Awkward moment/logic.
-            bundle.seq = self.counter - 1;
-            bundle.from = self.source;
-
-            if let Some(logger) = self.logging.as_ref() {
-                logger.log(MessagesEvent {
-                    is_send: true,
-                    channel: self.channel,
-                    source: self.source,
-                    target: self.target,
-                    seq_no: self.counter - 1,
-                    record_count: bundle.data.record_count(),
-                })
+pub use push_pull::{LogPusher, LogPuller};
+mod push_pull {
+
+    use crate::Accountable;
+    use crate::communication::{Push, Pull};
+    use crate::dataflow::channels::Message;
+    use crate::logging::{TimelyLogger as Logger, MessagesEvent};
+
+    /// Wraps a `Message<T,D>` pusher to provide a `Push<(T, Content<D>)>`.
+    #[derive(Debug)]
+    pub struct LogPusher<P> {
+        pusher: P,
+        channel: usize,
+        counter: usize,
+        source: usize,
+        target: usize,
+        logging: Option<Logger>,
+    }
+
+    impl<P> LogPusher<P> {
+        /// Allocates a new pusher.
+        pub fn new(pusher: P, source: usize, target: usize, channel: usize, logging: Option<Logger>) -> Self {
+            LogPusher {
+                pusher,
+                channel,
+                counter: 0,
+                source,
+                target,
+                logging,
             }
         }
-
-        self.pusher.push(pair);
     }
-}
 
-/// Wraps a `Message<T,D>` puller to provide a `Pull<(T, Content<D>)>`.
-#[derive(Debug)]
-pub struct LogPuller<P> {
-    puller: P,
-    channel: usize,
-    index: usize,
-    logging: Option<Logger>,
-}
+    impl<T, C: Accountable, P: Push<Message<T, C>>> Push<Message<T, C>> for LogPusher<P> {
+        #[inline]
+        fn push(&mut self, pair: &mut Option<Message<T, C>>) {
+            if let Some(bundle) = pair {
+                self.counter += 1;
+
+                // Stamp the sequence number and source.
+                // FIXME: Awkward moment/logic.
+                bundle.seq = self.counter - 1;
+                bundle.from = self.source;
+
+                if let Some(logger) = self.logging.as_ref() {
+                    logger.log(MessagesEvent {
+                        is_send: true,
+                        channel: self.channel,
+                        source: self.source,
+                        target: self.target,
+                        seq_no: self.counter - 1,
+                        record_count: bundle.data.record_count(),
+                    })
+                }
+            }
 
-impl<P> LogPuller<P> {
-    /// Allocates a new `Puller`.
-    pub fn new(puller: P, index: usize, channel: usize, logging: Option<Logger>) -> Self {
-        LogPuller {
-            puller,
-            channel,
-            index,
-            logging,
+            self.pusher.push(pair);
         }
     }
-}
 
-impl<T, C: Accountable, P: Pull<Message<T, C>>> Pull<Message<T, C>> for LogPuller<P> {
-    #[inline]
-    fn pull(&mut self) -> &mut Option<Message<T, C>> {
-        let result = self.puller.pull();
-        if let Some(bundle) = result {
-            let channel = self.channel;
-            let target = self.index;
-
-            if let Some(logger) = self.logging.as_ref() {
-                logger.log(MessagesEvent {
-                    is_send: false,
-                    channel,
-                    source: bundle.from,
-                    target,
-                    seq_no: bundle.seq,
-                    record_count: bundle.data.record_count(),
-                });
+    /// Wraps a `Message<T,D>` puller to provide a `Pull<(T, Content<D>)>`.
+    #[derive(Debug)]
+    pub struct LogPuller<P> {
+        puller: P,
+        channel: usize,
+        index: usize,
+        logging: Option<Logger>,
+    }
+
+    impl<P> LogPuller<P> {
+        /// Allocates a new `Puller`.
+        pub fn new(puller: P, index: usize, channel: usize, logging: Option<Logger>) -> Self {
+            LogPuller {
+                puller,
+                channel,
+                index,
+                logging,
             }
         }
+    }
 
-        result
+    impl<T, C: Accountable, P: Pull<Message<T, C>>> Pull<Message<T, C>> for LogPuller<P> {
+        #[inline]
+        fn pull(&mut self) -> &mut Option<Message<T, C>> {
+            let result = self.puller.pull();
+            if let Some(bundle) = result {
+                let channel = self.channel;
+                let target = self.index;
+
+                if let Some(logger) = self.logging.as_ref() {
+                    logger.log(MessagesEvent {
+                        is_send: false,
+                        channel,
+                        source: bundle.from,
+                        target,
+                        seq_no: bundle.seq,
+                        record_count: bundle.data.record_count(),
+                    });
+                }
+            }
+
+            result
+        }
     }
-}
+}
\ No newline at end of file
diff --git a/timely/src/dataflow/channels/pushers/exchange.rs b/timely/src/dataflow/channels/pushers/exchange.rs
index a9ea9b4fa..81e168c32 100644
--- a/timely/src/dataflow/channels/pushers/exchange.rs
+++ b/timely/src/dataflow/channels/pushers/exchange.rs
@@ -19,7 +19,7 @@ pub trait Distributor<C> {
     /// Flush any remaining contents into the `pushers` at time `time`.
     fn flush<T: Clone, P: Push<Message<T, C>>>(&mut self, time: &T, pushers: &mut [P]);
     /// Optionally release resources, such as memory.
-    fn relax(&mut self);
+    fn relax(&mut self) { }
 }
 
 /// A distributor creating containers from a drainable container based