nondeterminism: A monad and monad transformer for nondeterministic computations.

[ ai, constraints, control, failure, library, monads ] [ Propose Tags ]

Nondeterministic computations

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Versions [faq] 1.0, 1.2, 1.4
Dependencies base (>=4.8 && <5), containers, mtl (>=2 && <2.3) [details]
License LicenseRef-LGPL
Author Andrei Barbu <>
Maintainer Andrei Barbu <>
Revised Revision 1 made by HerbertValerioRiedel at Sat Jun 1 09:03:45 UTC 2019
Category Control, AI, Constraints, Failure, Monads
Source repo head: git clone
Uploaded by AndreiBarbu at Mon Oct 19 18:04:43 UTC 2015
Distributions LTSHaskell:1.4, NixOS:1.4, Stackage:1.4
Downloads 1471 total (71 in the last 30 days)
Rating 2.0 (votes: 1) [estimated by rule of succession]
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Status Hackage Matrix CI
Docs available [build log]
Last success reported on 2015-10-19 [all 1 reports]




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Readme for nondeterminism-1.2

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This package is available via Hackage where its documentation resides.

This provides nondeterministic computations in Haskell. It implements an Amb monad in which you can perform nondeterministic choices along with a monad transformer version, AmbT.


An example which finds Pythagorean triplets up to a certain size, project Euler problem 9.

import Control.Monad
import Control.Monad.Amb
pyTriple :: (Num t, Ord t) => t -> Amb r (t, t, t)
pyTriple n = do a <- anIntegerBetween 1 n
                b <- anIntegerBetween (a + 1) n
                c <- anIntegerBetween (b + 1) n
                when (a*a + b*b /= c*c) empty
                return (a,b,c)
length $ allValues $ pyTriple 100

More examples can be found in tests/test.hs.


  • allValues is not lazy in its return value