Decomposition and normalisation

[pevnak]

Hi,

these are implementations of those two functions we have discussed in the Setfield thread.
They works as

julia> optic = (@optic _.c) ∘ (@optic _.a.b)
(@optic _.c) ∘ (@optic _.b) ∘ (@optic _.a)

julia> optic.inner
(@optic _.b) ∘ (@optic _.a)

julia> optic.outer
(@optic _.a)

julia> normalise(optic).inner
(@optic _.a)

julia> normalise(optic).outer
(@optic _.c) ∘ (@optic _.b)

and

julia> decompose(@optic _.a.b.c.d)
((@optic _.d), (@optic _.c), (@optic _.b), (@optic _.a))

I have add docs and tests.

[jw3126]

Thanks a lot @pevnak ! What do you think @tkf ?

• I think decompose should go to CompositionsBase. What it does is
  decompose(sin ∘cos ∘ tan) === (sin, cos, tan).

• normalize does normalize((sin ∘ cos) ∘(tan ∘ cot)) === sin ∘ cos ∘ tan ∘ cot. It could also go to CompositionsBase.

jw3126/Setfield.jl#150

[pevnak]

U know we have talked about it, I just did not know, if it fits there an where?

Should I move it?

[jw3126]

Not sure if you are aware. But ComposedOptic is just an alias for ComposedFunction.
https://github.com/JuliaObjects/Accessors.jl/blob/master/src/optics.jl#L90

So if you define decompose(f::ComposedFunction) = ... then composed lenses will automatically work.
So you can just put decompose(...) at the bottom of https://github.com/JuliaFunctional/CompositionsBase.jl/blob/master/src/CompositionsBase.jl

About normalize, let's wait if @tkf has an opinion on where it should live.

[jw3126]

@pevnak lets keep normalization here and move decompose to CompositionsBase.jl

[jw3126]

Suggested change

	```julia
	```jldoctest```
	Similar below.

[jw3126]

Lets spell it the American way normalize to be consistent with julia base.

[jw3126]

Should be moved to CompositionsBase.jl

[jw3126]

Thanks looks good overall, just some minor remarks. Also, we should add a test, that normalize yields the compiler preferred composition order (I think this might be violated with your current implementation):
https://github.com/JuliaObjects/Accessors.jl/blob/master/test/perf.jl

[jw3126]

JuliaFunctional/CompositionsBase.jl#9

[jw3126]

@pevnak no idea if this is still relevant for you, but I added decompose here JuliaFunctional/CompositionsBase.jl#9

[aplavin]

Is any part of this PR relevant now that decompose has been in CompositionsBase for several years, @pevnak? The goal for normalize (another function introduced here) is not clear to me: the docstring seems to focus on a very specific case, not on general behavior.