Lack rule for `ifelse` about diffrules.jl HOT 5 CLOSED

Should be simple to add, and worth having IMO.

from diffrules.jl.

I was thinking it looks like this, but I'm not sure that false is actually the right thing... in Zygote etc. it would be nothing:

@define_diffrule Base.:ifelse(p, x, y) = :(false), :($p), :(!$p)

Trying this out with a package that uses this (old Zygote, maybe Tracker) would increase my confidence.

from diffrules.jl.

Most of the times ifelse can be replaced by combinations of max and mix which are included in DiffRules.jl.
Something like this https://exceljet.net/replace-ugly-ifs-with-max-or-min.

from diffrules.jl.

I raised this issue exactly because I want to avoid max and min combinations, but thanks for your suggestions.

from diffrules.jl.

I think it should be something like D(ifelse(condition, exp1, exp2)) = ifelse(condition, D(exp1), D(exp2)). If it is just this simple then I can make a little PR, but I don't know whether there are other potential issues.

from diffrules.jl.