Diffing

[vasilisp]

This patch implements a diffing algorithm. When a "set" operation is performed (either directly by the client, or via the implementation of make_from_s) we diff the old data structure contents with the new contents, and export incremental patches.

The diffing algorithm for lists is based on computing the longest common subsequence (based on standard recursion plus memoization). This is of quadratic complexity in the worst case, but I suspect our implementation performs decently in practice.

Most functions have gained an ?eq argument, which may be crucial for diffing; it depends on the contents. Note that diffing happens "early", e.g., if the input is a list of integers which is turned into a list of DOM nodes via map, then we diff lists of integers. In this example, there is no need to pass ~eq (the default (=) is just fine for integers). This early diffing means that we can avoid RPCs, DB queries, rebuilding DOM nodes and other complicated operations that happen downstream.

As a side-effect, the mutable lists kept internally have been replaced by signals. I think the new implementation of fold fixes #9.

[Drup]

This is great!
Since we have a diffing operation, we should change the API: make make_from_s the main entry function (and rename everything in a consistent fashion).

Also, I think we need a bench suite.

[Drup]

Also, please rename eq to equal, to make all the deriving-like libraries happy.

[vasilisp]

@Drup, React uses eq everywhere, and ReactiveData is closely tied to React. The benefit in connection to deriving would be marginal anyway, since we do not produce equality functions.

[Drup]

I meant this equal, not the labels.

[vasilisp]

Any further comments on this? It needs to get merged before the long-awaited Eliom release.

[Drup]

Let's merge, I'll try to come up with a good API later.