merge two ordered Producers into a new Producer.

provides a simple function to merge two Pipes-Producers into a new Producer that yields pairs of values of the original producers, but using Maybes to indicate values that are only present in the first, second or both producers. Useful to perform Left-Joins, Right-Joins and Inner-Joins on the fly using Haskell Pipes.

pipes-ordered-zip

A function to tie together two sorted Haskell Iterators (Producers from the pipes library).

Example:

import Pipes (runEffect, (>->), each)
import qualified Pipes.Prelude as P
import Pipes.OrderedZip (orderedZip)

main = do
    let a = each [1,  3,4,  6,8] -- assumed to be ordered
        b = each [  2,3,4,5,  8] -- assumed to be ordered
    let mergedProd = orderedZip compare a b
    _ <- runEffect $ mergedProd >-> P.print
    return ()

prints:

(Just 1,Nothing)
(Nothing,Just 2)
(Just 3,Just 3)
(Just 4,Just 4)
(Nothing,Just 5)
(Just 6,Nothing)
(Just 8,Just 8)

and

import Pipes (runEffect, (>->), each)
import qualified Pipes.Prelude as P
import Pipes.OrderedZip (orderedZipAll)

main = do
    let a = each ([1,  3,4,  6,  8] :: [Int])
        b = each ([  2,3,4,5,    8] :: [Int])
        c = each ([  2,3,  5,  7,8] :: [Int])
        mergedProd = orderedZipAll compare [a, b, c]
    _ <- runEffect $ mergedProd >-> P.print
    return ()

prints

[Just 1,Nothing,Nothing]
[Nothing,Just 2,Just 2]
[Just 3,Just 3,Just 3]
[Just 4,Just 4,Nothing]
[Nothing,Just 5,Just 5]
[Just 6,Nothing,Nothing]
[Nothing,Nothing,Just 7]
[Just 8,Just 8,Just 8]