F#+ Lenses

[wallymathieu]

• [x] Tests

Additional tests needed

• [x] write to array
• [x] write to object
• [x] write using _Type
• [x] write: what happens when index does not exists?
• [x] read: what happens when index does not exists?
• [ ] write: what happens when key does not exists?
• [x] read: what happens when key does not exists?

Starting to port lenses from lens-aeson

Note: Depends on pre release version of f#+

[gusty]

I don't think we need to change to Result to implement F#+ lenses.

However it would make sense for this library to switch to Result, but IMHO we should treat it as a separate issue.

[wallymathieu]

Yes, that makes sense.

[wallymathieu]

I'll fix it after the next f#+ release

[wallymathieu]

We need to verify that usage of the lenses doesn't cause to much of a slowdown when used.

[gusty]

If they do so, it may be worth exploring other lens implementations, based on Data.Lens and add PR to F#+ to a different namespace.

[wallymathieu]

I'm not sure lenses are needed as much for JSON data, since the format is inherently mutable.

[gusty]

I think there are valid scenarios for lenses here. Anyway I'm not sure if Control Lenses are really needed.

As Json is dynamic, we might not need polymorphic updates.

But, then the first step would be to create Data.Lenses, possibly with the same interface (operators, functions and lenses).

[wallymathieu]

Sounds like a plan 😄

[wallymathieu]

It would be nice of you could mix them somehow?

[wallymathieu]

The compilation cost of lenses are now negligible! Awesome work @gusty !

[wallymathieu]

Compilation times:

• No lenses: Time Elapsed 00:00:45.90
• F#+ 1.1.0-CI00230 lenses: Time Elapsed 00:02:10.57
• F#+ 1.1.0-CI00240 lenses: Time Elapsed 00:01:03.53
• F#+ 1.1.0-light-lenses lenses: Time Elapsed 00:00:44.95 https://github.com/fsprojects/FSharpPlus/commit/8f6218d3d8c4e55c009ee6627dd8c549bd01e15c