Dimensional counters

[lucasdicioccio]

No description provided.

[lucasdicioccio]

This change breaks consumers of the API, and maybe some old GHC/Base versions. (Built with The Glorious Glasgow Haskell Compilation System, version 8.2.2).

I plan to wrap the new module with a type-fancy layer (either in this package or in another package) for a stronger guarantee that the dimensions passed to lookupOrCreate are correct (possibly saving a runtime check about dimension lengths).

Minimal compatibility patches to demonstrate the feature are provided for ekg-json and ekg.

• https://github.com/lucasdicioccio/ekg-json/tree/dimensional-counters
• https://github.com/lucasdicioccio/ekg/tree/dimensional-counters

The example works and displays individual curves flattening the dimensions as follows.

I'm more interested in providing support into ekg-core than ekg. Though, I don't mind doing a bit more. In particular, one annoying issue of my current design is the lack of "forced ordering" on the key/value pairs for the dimensions: thus preventing the ekg Snap layer to guess the HashMap key for retrieving a particular Sample value (but I'm not aware of users of this Snap route and I would suggest to drop the feature rather than complexifying the ekg-core logic for no users).

[lucasdicioccio]

@tibbe any comment about this MR?

I'm willing to provide a typeful layer above this one to enforce more type-safety between the construction and consuming sides, though it should probably go in another package where we can allow stricter GHC versions.

[tibbe]

@23Skidoo is the main reviewer now but I added some comments.

[tibbe]

Please stick to the field naming pattern used for other data types (i.e. no leading underscore, but prefixed as needed).

[tibbe]

This belongs in the examples/ directory and/or in some docs.

[tibbe]

Lots of Haddoc docs needed here.

[tibbe]

This file needs some top-level Haddocks explaining how to use this module and what it's for.

[23Skidoo]

Closing in favour of #32.

[lucasdicioccio]

Thanks @matth-