Practicalities of Incorporating Existing ChainRules

[willtebbutt]

Incorporating a specific ChainRule that has already been written is entirely straightforward. Precisely how an entire library of ChainRules ought to be incorporated is another matter. For example, probably most of the ChainRules in SpecialFunctions.jl will work fine in this system (i.e. there won't be any type problems), but we really need to decide whether or not to incorporate them on a case-by-case basis.

One option is to create a package extension to this package which manually chooses which rules to incorporate. This might provide a decent hack, but obviously won't keep up to date with SpecialFunctions.jl.

[yebai]

It’s a sensible idea to begin with.

[willtebbutt]

Note: we now have an actual example of doing this in practice here. It's done entirely manually, but it demonstrates the core point (that it's entirely straightforward to combine ChainRules.rrules with rrule!!s).

(This obviously isn't the end point of this line of work, but it does demonstrate a practical working example of this)

[willtebbutt]

I'm closing this via #88 , which introduces a macro for defining rrule!!s using rrules.