Rewriting the Dictionary structure in Elm

[mroman42]

As explained in #5, an Elm Dict needs the type of its keys to be comparable, and only a few primitive types are comparable. Because of that, it is not possible to use the core containers (Set, Dict) with user-defined data types.

It is more efficient to update a Dict a b than a -> b. That's why I find that a well-behaved dictionary structure could help us to define Graphs. It is easier to update with new edges and vertices.

An alternative approach is just to maintain the same a -> b and to do the updates as follows:

update : (a -> b) -> a -> b -> (a -> b)
update f x y z = if z == x then y else (f z)

[mroman42]

I have completely rewrote the elm-core Dict structure to make it possible to use an arbitrary comparator. It can be seen in the newDict branch.

[mroman42]

It is working as expected.