Dict.first, Dict.last, Set.first, Set.last

[billstclair]

I have an application that needs to process the elements of a Set one at a time. Currently, the only way to get an element from a set is to convert it to a list and take an element of the list. It's quicker and conses less to just get the first or last element out of the internal storage, and use that.

Since Set is based on Dict, I added first and last to both.

My current code:

popSet : Set comparable -> Maybe (comparable, Set comparable)
popSet set =
    case Set.toList set of
        [] ->
            Nothing
        res :: _ ->
            Just (res, Set.remove res set)

With these changes:

popSet : Set comparable -> Maybe (comparable, Set comparable)
popSet set =
    case Set.first set of
        Nothing ->
            Nothing
        Just res ->
            Just (res, Set.remove res set)

[process-bot]

Thanks for the pull request! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[process-bot]

Thanks for the pull request! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[Skinney]

You'll have more luck trying to add this to elm-community/dict-extra.

[Skinney]

You'll have more luck trying to add this to elm-community/dict-extra.

[billstclair]

@Skinney I currently use in my code an implementation based on Set.toList and Dict.toList. The purpose of this patch is to make that faster with no memory allocation by using the internals of the opaque Set and Dict types. That can't be done in elm-community/dict-extra.

[billstclair]

@Skinney I currently use in my code an implementation based on Set.toList and Dict.toList. The purpose of this patch is to make that faster with no memory allocation by using the internals of the opaque Set and Dict types. That can't be done in elm-community/dict-extra.

[myrho]

+1

The elm-community/intdict also has this already. It's called findMin and findMax there.

[myrho]

+1

The elm-community/intdict also has this already. It's called findMin and findMax there.

[evancz]

At some point we will do a review of the *-extras and bring things in. These seem like good candidates because of their asymptotics, but there are other Dict changes that mean it will be easier to just do the changes by hand, rather than through PR.

[evancz]

At some point we will do a review of the *-extras and bring things in. These seem like good candidates because of their asymptotics, but there are other Dict changes that mean it will be easier to just do the changes by hand, rather than through PR.