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Editorial Team
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Asked: 2026-06-17T06:53:43+00:00

I’m trying to use IxSet for database-like purposes, so I’ve built an index of

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I’m trying to use IxSet for database-like purposes, so I’ve built an index of items and I need to do exact match on some field.

Query operator (@=) http://hackage.haskell.org/packages/archive/ixset/1.0.2/doc/html/Data-IxSet.html#v:-64–61- returns an IxSet a type, but I need only to either get 1 or 0 results. To check if it’s 0 results, I do null items on that, but how do I get first item?

Due to description of IxSet type http://hackage.haskell.org/packages/archive/ixset/1.0.5/doc/html/Data-IxSet.html#t:IxSet I don’t see any typeclass that has operation like head or fst.

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  1. Editorial Team

    Ok, found an answer. You should use some available function like getOne http://hackage.haskell.org/packages/archive/ixset/1.0.5/doc/html/Data-IxSet.html#v:getOne , for example.

    p.s.: I find that a bit strange to first create your type from list of items and then add operations that duplicate list-operations, but maybe I’m just newbie 🙂

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