# Using Immutable Vector extractors on Mutable Vectors

**URL:** <https://discourse.haskell.org/t/using-immutable-vector-extractors-on-mutable-vectors/4928>\
**Category:** Learn\
**Created:** [August 13, 2022, 9:40am UTC](https://discourse.haskell.org/t/using-immutable-vector-extractors-on-mutable-vectors/4928 "2022-08-13T09:40:06Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**Author:** ![kalhauge](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/kalhauge/32/2827_2.png) [@kalhauge](https://discourse.haskell.org/u/kalhauge)\
**Post date:** [August 13, 2022, 9:48pm UTC](https://discourse.haskell.org/t/using-immutable-vector-extractors-on-mutable-vectors/4928/9 "2022-08-13T21:48:24Z")

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I’m looking at the ‘countBits’ and ‘nthBitIndex’, there does not seem to be mutable versions of the same operations. I’m specifically trying to implement a succinct dictionary to improve the storage of a data structure I’m working on in the [http://discourse.haskell.org/t/counting-words-but-can-we-go-faster/](http://discourse.haskell.org/t/counting-words-but-can-we-go-faster/) project.

Ps. Always happy to talk to the author of the library 🙂

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