Control.Concurrent.CHP.Common

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

or:

 import qualified Control.Concurrent.CHP.Common as CHP

to circumvent this problem.

Documentation

labelMe :: String -> a -> a

id :: (ReadableChannel r, Poisonable (r a), WriteableChannel w, Poisonable (w a)) => r a -> w a -> CHP ()

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

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

Forever forwards the value onwards. This is like id but does not add any buffering to your network, and its presence is indetectable to the process either side.

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

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

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 -- except when the readers of the channels are offering a choice).

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

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

tail :: Chanin a -> Chanout a -> CHP ()

Discards the first value it receives then act likes id.

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

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

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

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

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

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. If you require a strict transformation, use map'.

map' :: NFData b => (a -> b) -> Chanin a -> Chanout b -> CHP ()

Like map, but applies the transformation strictly before sending on the value.

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

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 ()

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 ()

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 ()

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

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

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 ()

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

consumeAlongside :: Chanin a -> CHP b -> CHP b

For the duration of the given process, acts as a consume process, but stops when the given process stops. Note that there could be a timing issue where extra inputs are consumed at the end of the lifetime of the process. Note also that while poison from the given process will be propagated on the consumption channel, there is no mechanism to propagate poison from the consumption channel into the given process.

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

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.

joinList :: [Chanin a] -> Chanout [a] -> CHP ()

Forever reads a value from all its input channels in parallel, then joins the values into a list in the same order as the channels, and sends them out again.

split :: Chanin (a, b) -> Chanout a -> Chanout b -> CHP ()

Forever reads a pair from its input channel, then in parallel sends out the first and second parts of the pair on its output channels.

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

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 ()

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

valueStore :: (ReadableChannel r, Poisonable (r a), WriteableChannel w, Poisonable (w a)) => a -> r a -> w a -> CHP ()

A shared variable process. Given an initial value and two channels, it continually offers to output its current value or read in a new one.

valueStore' :: (ReadableChannel r, Poisonable (r a), WriteableChannel w, Poisonable (w a)) => r a -> w a -> CHP ()

A shared variable process. The same as valueStore, but initially waits to read its starting value before then offering to either output its current value or read in a new one.

advanceTime :: (Waitable c, Ord t) => (t -> t) -> Enrolled c t -> CHP ()

Continually waits for a specific time on the given clock, each time applying the function to work out the next specific time to wait for. The most common thing to pass is Prelude.succ or (+1).