chp-1.0.1: An implementation of concurrency ideas from Communicating Sequential Processes



A collection of useful common processes that are useful when plumbing together a process network. All the processes here rethrow poison when it is encountered, as this gives the user maximum flexibility (they can let it propagate it, or ignore it).

The names here overlap with standard Prelude names. This is deliberate, as the processes act in a similar manner to the corresponding Prelude versions. It is expected that you will do something like:

 import qualified Control.Concurrent.CHP.Common as Common


 import qualified Control.Concurrent.CHP.Common as CHP

to circumvent this problem.



id :: Chanin a -> Chanout a -> CHP ()Source

Forever forwards the value onwards, unchanged. Adding this to your process network effectively adds a single-place buffer.

extId :: Chanin a -> Chanout a -> CHP ()Source

Forever forwards the value onwards, in an extended rendezvous. This is like id but does not add any buffering to your network.

extId is a unit of the associative operator |->|.

tap :: Chanin a -> [Chanout a] -> CHP ()Source

A process that waits for an input, then sends it out on all its output channels (in order) during an extended rendezvous. This is often used to send the output on to both the normal recipient (without introducing buffering) and also to a listener process that wants to examine the value. If the listener process is first in the list, and does not take the input immediately, the value will not be sent to the other recipients until it does. The name of the process derives from the notion of a wire-tap, since the listener is hidden from the other processes (it does not visibly change the semantics for them).

prefix :: a -> Chanin a -> Chanout a -> CHP ()Source

Sends out a single value first (the prefix) then behaves like id.

succ :: Enum a => Chanin a -> Chanout a -> CHP ()Source

Forever reads in a value, and then sends out its successor (using succ).

parDelta :: Chanin a -> [Chanout a] -> CHP ()Source

Reads in a value, and sends it out in parallel on all the given output channels.

map :: (a -> b) -> Chanin a -> Chanout b -> CHP ()Source

Forever reads in a value, transforms it using the given function, and sends it out again. Note that the transformation is not applied strictly, so don't assume that this process will actually perform the computation.

filter :: (a -> Bool) -> Chanin a -> Chanout a -> CHP ()Source

Forever reads in a value, and then based on applying the given function either discards it (if the function returns false) or sends it on (if the function returns True).

stream :: Traversable t => Chanin (t a) -> Chanout a -> CHP ()Source

Streams all items in a Traversable container out in the order given by mapM on the output channel (one at a time). Lists, Maybe, and Set are all instances of Traversable, so this can be used for all of those.

merger :: [Chanin a] -> Chanout a -> CHP ()Source

Forever waits for input from one of its many channels and sends it out again on the output channel.

replicate :: Int -> a -> Chanout a -> CHP ()Source

Sends out the specified value on the given channel the specified number of times, then finishes.

repeat :: a -> Chanout a -> CHP ()Source

Forever sends out the same value on the given channel, until poisoned. Similar to the white-hole processes in some other frameworks.

consume :: Chanin a -> CHP ()Source

Forever reads values from the channel and discards them, until poisoned. Similar to the black-hole processes in some other frameworks.

join :: (a -> b -> c) -> Chanin a -> Chanin b -> Chanout c -> CHP ()Source

Forever reads a value from both its input channels in parallel, then joins the two values using the given function and sends them out again. For example, join (,) c d will pair the values read from c and d and send out the pair on the output channel, whereas join (&&) will send out the conjunction of two boolean values, join (==) will read two values and output whether they are equal or not, etc.

sorter :: Ord a => Chanin (Maybe a) -> Chanout (Maybe a) -> CHP ()Source

A sorter process. When it receives its first Just x data item, it keeps it. When it receieves a second, it keeps the lowest of the two, and sends out the other one. When it receives Nothing, it sends out its data value, then sends Nothing too. The overall effect when chaining these things together is a sorting pump. You inject all the values with Just, then send in a single Nothing to get the results out (in reverse order).

sorter' :: forall a. (a -> a -> Bool) -> Chanin (Maybe a) -> Chanout (Maybe a) -> CHP ()Source

Like sorter, but with a custom comparison method. You should pass in the equivalent of less-than: (<).