# Scan or not to scan?

**URL:** <https://discourse.elm-lang.org/t/scan-or-not-to-scan/2429>\
**Category:** Learn\
**Created:** [November 3, 2018, 8:07am UTC](https://discourse.elm-lang.org/t/scan-or-not-to-scan/2429 "2018-11-03T08:07:27Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![David\_Legard](https://avatars.discourse-cdn.com/v4/letter/d/e79b87/32.png) [@David\_Legard](https://discourse.elm-lang.org/u/David_Legard)\
**Post date:** [November 3, 2018, 8:07am UTC](https://discourse.elm-lang.org/t/scan-or-not-to-scan/2429/1 "2018-11-03T08:07:27Z")

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In the core 5.1.1 package documentation, I can see the definition of the common functional programming function List.scanl.

But the compiler doesn’t recognise it:

```
I cannot find a `List.scanl` variable:

The `List` module does not expose a `scanl` variable. These names seem close
though:

```

Any thoughts?

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**Author:** ![jessta](https://yyz1.discourse-cdn.com/flex035/user_avatar/discourse.elm-lang.org/jessta/32/660_2.png) [@jessta](https://discourse.elm-lang.org/u/jessta)\
**Post date:** [November 3, 2018, 9:45am UTC](https://discourse.elm-lang.org/t/scan-or-not-to-scan/2429/2 "2018-11-03T09:45:40Z")

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You’re looking at the documentation for the core package for Elm 0.18. (`elm-lang/core`)

`List.scanl` was removed in Elm 0.19 and core was moved to `elm/core`.  
[https://package.elm-lang.org/packages/elm/core/latest/List](https://package.elm-lang.org/packages/elm/core/latest/List)

You can use the `scanl` function from `elm-community/list-extra`  
[https://package.elm-lang.org/packages/elm-community/list-extra/latest/List-Extra#scanl](https://package.elm-lang.org/packages/elm-community/list-extra/latest/List-Extra#scanl)

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<div class="post-metadata">

**Author:** ![David\_Legard](https://avatars.discourse-cdn.com/v4/letter/d/e79b87/32.png) [@David\_Legard](https://discourse.elm-lang.org/u/David_Legard)\
**Post date:** [November 3, 2018, 11:56pm UTC](https://discourse.elm-lang.org/t/scan-or-not-to-scan/2429/3 "2018-11-03T23:56:09Z")

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Thanks for the info.

In general terms, is there any easy way to tell which piece of documentation is 0.18 or 0.19 – is there a cast-iron way to guarantee being on the latest documentation?

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**Author:** ![malaire](https://avatars.discourse-cdn.com/v4/letter/m/b782af/32.png) [@malaire](https://discourse.elm-lang.org/u/malaire)\
**Post date:** [November 4, 2018, 12:30am UTC](https://discourse.elm-lang.org/t/scan-or-not-to-scan/2429/4 "2018-11-04T00:30:54Z")

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> [@David\_Legard](#):
>
> In general terms, is there any easy way to tell which piece of documentation is 0.18 or 0.19 – is there a cast-iron way to guarantee being on the latest documentation?

Search for package in [http://package.elm-lang.org/](http://package.elm-lang.org/) - that only shows 0.19 packages.

And there is also [Elm 0.18 packages](https://dmy.github.io/elm-0.18-packages/) for 0.18 packages.

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<div class="post-metadata">

**Author:** ![David\_Legard](https://avatars.discourse-cdn.com/v4/letter/d/e79b87/32.png) [@David\_Legard](https://discourse.elm-lang.org/u/David_Legard)\
**Post date:** [November 4, 2018, 12:43am UTC](https://discourse.elm-lang.org/t/scan-or-not-to-scan/2429/5 "2018-11-04T00:43:41Z")

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Also, [https://package.elm-lang.org/packages/elm-lang/core/latest](https://package.elm-lang.org/packages/elm-lang/core/latest) shows 0.18 documentation, which is the trap I fell into - that is where my bookmark pointed…

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<div class="post-metadata">

**Author:** ![malaire](https://avatars.discourse-cdn.com/v4/letter/m/b782af/32.png) [@malaire](https://discourse.elm-lang.org/u/malaire)\
**Post date:** [November 4, 2018, 12:46am UTC](https://discourse.elm-lang.org/t/scan-or-not-to-scan/2429/6 "2018-11-04T00:46:48Z")

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Yes, it’s a bit confusing. Both 0.18 and 0.19 packages will be located at [http://package.elm-lang.org/packages/](http://package.elm-lang.org/packages/)… but the search engine at [http://package.elm-lang.org](http://package.elm-lang.org) only shows 0.19 packages.

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**Author:** ![system](https://canada1.discourse-cdn.com/flex035/uploads/elm_lang/original/1X/50a05e53677a2c3b47776d7abd0f113eb50193a1.png) [@system](https://discourse.elm-lang.org/u/system)\
**Post date:** [November 14, 2018, 12:55am UTC](https://discourse.elm-lang.org/t/scan-or-not-to-scan/2429/7 "2018-11-14T00:55:49Z")

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