Dict.union (Dict.singleton, Dict.singleton)

[gampleman]

What the rule should do:

Dict.union (Dict.singleton "foo" "bar") (Dict.singleton "some" other)

-->

Dict.fromList [( "foo", "bar" ), ( "some", other )]

---

Dict.union (Dict.singleton "foo" "bar") (Dict.fromList [("some", other)])

-->


Dict.fromList [( "foo", "bar" ), ( "some", other )]

this already happens for Dict.fromList, but this expands it to work with Dict.singleton. Basically anywhere we use Dict.fromList, we should also work with Dict.singleton.

[gampleman]

We could also potentially do something with the fact that Dict.union (Dict.singleton key value) dict) is equivalent to Dict.insert key value dict.

[lue-bird]

Right. so additionally:

Dict.union (Dict.singleton k v) dict
--> Dict.insert k v dict

Set.union (Set.singleton a) set
--> Set.insert a set
Set.union set (Set.singleton a)
--> Set.insert a set
Set.union (Set.singleton a) (Set.singleton b)
--> Set.fromList [ a, b ]

The only objection to your initial proposal I can see is that Dict.fromList [ (ka,va), (kb,vb) ] will be slower than Dict.insert kb vb (Dict.singleton ka va) (which is why I always use the second form). simplify also currently doesn't do the transformation to fromList when inserting into singleton.

I think I can work on these unless someone else wants to or opposes them.