dejafu

Overloadable primitives for testable, potentially non-deterministic, concurrency.

https://github.com/barrucadu/dejafu

Version on this page:0.1.0.0@rev:1
LTS Haskell 24.28:2.4.0.7
Stackage Nightly 2026-01-14:2.4.0.8
Latest on Hackage:2.4.0.8

See all snapshots dejafu appears in

MIT licensed by Michael Walker
Maintained by [email protected]
This version can be pinned in stack with:dejafu-0.1.0.0@sha256:935e76d2b0fc8f25addcc95aebeee736642fe341f7c29c9a688be6ba0b84f0ad,3940

Module documentation for 0.1.0.0

[Déjà Fu is] A martial art in which the user's limbs move in time as well as space, […] It is best described as "the feeling that you have been kicked in the head this way before" -- Terry Pratchett, Thief of Time

Concurrency is nice, deadlocks and race conditions not so much. The Par monad family, as defined in abstract-par provides deterministic parallelism, but sometimes we can tolerate a bit of nondeterminism.

This package provides a class of monads for potentially nondeterministic concurrency, with an interface in the spirit of GHC's normal concurrency abstraction.

MonadConc with IO:

The intention of the MonadConc class is to provide concurrency where any apparent nondeterminism arises purely from the scheduling behaviour. To put it another way, a given computation, parametrised with a fixed set of scheduling decisions, is deterministic. This assumption is used by the testing functionality provided by Test.DejaFu.

Whilst this assumption may not hold in general when IO is involved, you should strive to produce test cases where it does.

See the README for more details.