[Haskell-cafe] wanted: Function to break circular data dependencies

Erik Hesselink hesselink at gmail.com
Tue May 6 10:24:59 UTC 2014

On Tue, May 6, 2014 at 11:38 AM, Chris Warburton
<chriswarbo at googlemail.com> wrote:
> Job Vranish <job.vranish at gmail.com> writes:
>> I've often found myself wanting a function like this. It would make certain
>> kinds of knot-tying/cycle detection _much_ easier.
>> Is there any reason why this function can't/shouldn't exist?
> This makes me think of the more widely-known 'parallel OR' operator,
> which evaluates its arguments in parallel and returns whichever finishes
> evaluating first.
> This operator cannot be implemented in Lambda Calculus, but it can in
> Haskell (via threads). Unfortunately Googling for 'haskell "parallel
> or"' brings up sentence fragments ('...parallel or concurrent...')
> rather than a parallel or implementation.

Perhaps you are looking for 'unamb' [0]?


[0] http://hackage.haskell.org/package/unamb

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