Base.Meta.ParseError("invalid operator \"--\"") when multiprocessing

Hello,

I'm using your package with a huge list of expression.
Basically, I'm doing this:

`res = map(exp -> (exp, rcall(exp)), res)`

It run correctly but it is taking forever and my CPU is barely used.

So I wanted to speed things up with multiprocessing. I tried with [pmap](https://docs.julialang.org/en/v1.1/stdlib/Distributed/#Distributed.pmap), [@threads](https://docs.julialang.org/en/v1.1/base/multi-threading/#Base.Threads.@threads), [@spawn](https://docs.julialang.org/en/v1.1/stdlib/Distributed/#Distributed.@spawn) and [@distributed](https://docs.julialang.org/en/v1.1/stdlib/Distributed/#Distributed.@distributed) and starting with `julia -p 6` in deed.

Most of the time I get this error :
```
ERROR: LoadError: On worker 2:
Base.Meta.ParseError("invalid operator \"--\"")
```
Or no error but no increase in speed (and CPU < 10%).

Moreover, I have this error without doing any multiprocessing.
With the same code I can crash if I start `julia ./script.jl`
but I don't crash inside the REPL `julia> include("GenerateFormula4.jl")`
I'm using Windows 10.

I'm still new to Julia so I'm not sure what could cause the problem.