You should not need to include the same file multiple times in Julia, so the answer to your question is “don’t do that”. This is an important difference between the way Julia and C++ are used. Instead, you can do:
module A
include("B.jl")
using .B
module C
using ..B
end
end
Where B.jl looks like:
module B
...
end
The using ..B
line lets you load the B module from A inside C without having to include it twice.