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== Abstract ==
'''unamb''' is a package containing the ''unambiguous choice'' operator <hask>unamb</hask>, which wraps thread racing up in a purely functional, semantically simple wrapper.
Given any two arguments <hask>u</hask> and <hask>v</hask> that agree unless bottom, the value of <hask>unamb u v</hask> is the more terminating of <hask>u</hask> and <hask>v</hask>.
Operationally, the value of <hask>unamb u v</hask> becomes available when the earlier of <hask>u</hask> and <hask>v</hask> does.
The agreement precondition ensures unamb's referential transparency.
For more info about <hask>unamb</hask> and its use, see the paper ''[ Simply Efficient Functional Reactivity]'', sections 10 and 11.
<hask>unamb</hask> was originally a part of [[Reactive]]. I moved it to its own package in order to encourage experimentation.
Besides this wiki page, here are more ways to find out about unamb:
* Visit the [ Hackage page] for library documentation and to download & install.
* Read [ related blog posts].
* Or install with <tt>cabal install unamb</tt>.
* Get the code repository: <tt>darcs get</tt>.
<!-- * See the [[unamb/Versions| version history]]. -->
<!-- Please leave comments at the [[Talk:unamb|Talk page]]. -->
See also the [[lub]] package, which extends unamb's usefulness with non-flat types.
== Issues ==
As of version 0.1.1, unamb requires ghc 6.10 or better.
As of version 0.1.6, unamb correctly handles recursive termination of sub-efforts and automatic restarting, but only with the GHC RTS fixes that first appeared (stably, by my testing) in GHC HEAD version 6.11.20090115.
The problems and solution can be found in a few places:
* Email thread: ''[ Problem with unamb -- doesn't kill enough threads]''
* Blog post: ''[ Smarter termination for thread racing]''
* Email thread: ''[ Black hole detection and concurrency]''