insert should append a value?

[amitaibu]

Currently we prepend the new value and it appears on the top of the list.

assoc-list/src/AssocList.elm

Line 191 in 63ffd69

D (( key, value ) :: alteredAlist)

This means that if we have a list

[ ( 1, 1 ), ( 2, 2 ), ( 3, 3 ), ( 4, 4 ) ] |> Dict.fromList

results with D [(4,4),(3,3),(2,2),(1,1)]

I'd expect the list order to remain as is, or is there a good reason not to?

[amitaibu]

Another good example is

[ ( 1, 1 ), ( 2, 2 ), ( 3, 3 ), ( 4, 4 ) ] 
    |> Dict.fromList 
    |> Dict.toList

ends up with [(4,4),(3,3),(2,2),(1,1)]

[pzp1997]

I agree with you that the behavior is a bit surprising. This was one of the aspects of the library that I was the most unsure about before publishing. The reason fromList reverses the list is because it uses List.foldl rather than List.foldr. At the time this seemed like the right choice to me for two reasons, List.foldl is a bit faster and it is what elm/core Dict uses in its fromList implementation. In hindsight, this decision feels more and more like a mistake to me.

With regards to changing insert, that is not a great way to solve this problem since appends are way slower than conses both in theory and in practice. We could do a trick by writing a combined filter-and-append operation using List.foldr but it seems like more trouble than its worth given that there's an even simpler fix involving fromList. In short, the "problem" is with fromList not insert.

I want to make the change to fromList but might need to wait for another breaking change so I can batch them and trick Elm's automatic semver enforcement into accepting this as a major bump.

[amitaibu]

Hi, just checking if there's a plan to change this soon? (currently I'm running a local patched lib, but would be happy to use upstream)

[pzp1997]

I am going to try to release a new version once I am done with school in about two weeks and I expect this change to be included. Hang in there!

[amitaibu]

Hi 👋

Anything I can help to get it forward? I just added the forked file to the 4th Gizra project, and I feel bad about it every time! 😉

[amitaibu]

Hi @pzp1997 are you still interested in this fix? We're now at the ~7th project with our own fork.