Portability | portable |
---|---|
Stability | experimental |
Maintainer | dustin.deweese@gmail.com |
Safe Haskell | Safe-Infered |
- Computation type:
- Computations that both consume and produce elements lazily with support for advanced control flow using continuations
- Binding Strategy:
- Binding a function to a monadic value produces a continuation which passes the unconsumed input and the combined output function in turn to the next continuation.
- Useful for:
- Lazily processing a list with complex control structures.
- Zero and plus:
- None.
- Example type:
-
Catana
i o b a
The Catana monad represents computations that are both catamorphisms and anamorphisms; they both consume and produce values. In addition, the Catana monad represents the computation in continuation-passing style, and implements callCC.
- data Catana i o b a = Catana {
- runCatana :: (a -> Step i o b) -> Step i o b
- consume :: Catana i o a i
- top :: Catana i o a i
- push :: i -> Catana i o a ()
- produce :: o -> Catana i o a ()
- stop :: b -> Catana i o b a
- evalCatana :: Catana i o a a -> [i] -> [o]
- evalCatana' :: Catana i o a a -> [i] -> (Maybe a, [o])
- parallelB :: Catana i o a a -> Catana i o b b -> Catana i o c (a, b)
- parallelE :: Catana i o a a -> Catana i o b b -> Catana i o c (Either a b)
- serial :: Catana io o a a -> Catana i io b b -> Catana i o c (Either a b)
The Catana monad
consume :: Catana i o a iSource
Consumes an element from the input list, returning it If there is no more input, the chain of continuations ends immediately; no more computations will be processed
evalCatana :: Catana i o a a -> [i] -> [o]Source
Converts a Catana monad into a function over lists
evalCatana' :: Catana i o a a -> [i] -> (Maybe a, [o])Source
Evaluates a Catana monad over a list returning the result and output
parallelB :: Catana i o a a -> Catana i o b b -> Catana i o c (a, b)Source
Combine two monads to run in parallel, consuming the same input
parallelE :: Catana i o a a -> Catana i o b b -> Catana i o c (Either a b)Source
Combine two monads to run in parallel, consuming the same input, stopping when either of them finish.
serial :: Catana io o a a -> Catana i io b b -> Catana i o c (Either a b)Source
Combine two monads to run in serial, the first consuming the output of the second
Example 1: Usage of the Catana monad
An example of complex control structure using Catana:
catanaExample1 = forever $ do z <- callCC $ \exit -> do (x, y) <- (,) <$> consume <*> consume produce (x + y) produce (x * y) if x > 1 then exit 0 else do produce (x - y) produce (x / y) return 1 produce z
Catana monads can be converted into a function over lists using evalCatana
.
evalCatana catanaExample1 [1..4] -- result: [3.0,2.0,-1.0,0.5,1.0,7.0,12.0,0.0]
An example using serial and parallel data flow:
catanaExample2 = sq `serial` (ev `parallelB` od) where od = forever $ do x <- consume when (odd x) . produce $ x * 2 ev = forever $ do x <- consume when (even x) . produce $ x + 3 sq = forever $ do x <- consume produce x produce $ x ^ 2
let l = 1 : evalCatana catanaExample2 l take 10 l -- result: [1,2,4,5,25,7,49,10,100,50]