Melding Monads

2009 June 22

Control.Monad.Queue

Filed under: continuations, corecursion, haskell, monads, queues — lpsmith @ 8:41 pm

Haskell aficionados, take note! My library for corecursive queues has now been uploaded to Hackage. You can now cabal-install it.

I also have a substantially revised draft of the associated paper, Lloyd Allison’s Corecursive Queues, available. It has been re-organized so that it is hopefully easier to follow, it includes a careful performance comparison, and a tentative proof that mapCont cannot be expressed in terms of callCC, (>>=), return.

The library includes a somewhat crude micro-benchmarking program in the tests/ directory. Those who have read previous drafts, be warned that the few brief statements about performance were based on past notes, and I found some several issues with the testing methodology contained in the notes. Here the revised results:

Description Time (ms) -H500M Bytes allocated
GHC 6.10.3 mean σ mean σ per Branch
levelOrder’ 446 5 172 15 44.0
CorecQ 555 5 619 4 133.5
CorecQW _ 696 5 1128 6 213.6
CorecQW () 907 56 2235 11 213.6
Side Channel _ 959 3 1171 7 228.7
Side Channel () 1500 56 2171 7 276.4
STQ 1140 8 1087 14 371.2
TwoStack 1158 4 778 10 185.8
Okasaki 1553 7 1574 12 209.0
Data.Sequence 962 5 1308 5 348.1
GHC 6.8.3
levelOrder’ 461 2 173 15 44.1
CorecQ 458 4 267 13 67.5
CorecQW _ 526 5 713 5 141.2
CorecQW () 781 62 1775 62 141.3

These benchmarks come from performing breadth-first traversals repeatedly on the 34th fibonacci tree, on an Intel Core 2 Duo T9550. The first few data points were discarded, and the mean and standard deviation of the remaining times were computed. Note that getCPUTime was used to time each run, and this has a resolution of only 10 milliseconds.

If you would like to play with the queue transformer, which doesn’t appear in the library, or other bits of code exactly as they appear in the paper, you can download the source code here.

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