Accessing variables in Main within a Module using RCall

New to Julia
, , ,
1

I would like to access variables declared in Main from within a module but they’re not in scope and I wonder how this can be achieved.

using RCall

x = 1

f(var::String) = eval(Meta.parse("@rput ("*var*")"))

module M1
using RCall
import RCall: @rput 

f(var::String) = eval(Meta.parse("@rput ("*var*")"))

end

julia> f("x")
1

julia> M1.f("x")
ERROR: UndefVarError: x not defined

julia> M1.f("Main.x")
ERROR: LoadError: Incorrect usage of @rput
2

You can use fully qualified variable name

julia> M1.f("Main.x")
1

Alternatively you can import names into module

module M1
using Main: x
f(var::String) = eval(Meta.parse("println("*var*")"))
end

julia> M1.f("x")
1
3

Hi @Skoffer

Thank you very much for your answer, unfortunately I simplified the problem too much.
I am using @rput from the RCall package and @rput Main.x returns and error. I just updated the original post with an slightly less simplified example.

4

It is rather difficult to understand eval functions. Each module has its own eval(x), which evaluates expressions in that module (= name space).

using RCall

x = 1

f(var::String) = eval(:(@rput($(Symbol(var)))))

module M2

using RCall

x = 2

f(var::String) = eval(:(@rput($(Symbol(var)))))
g(var::String) = Main.eval(:(@rput($(Symbol(var)))))
g(m::Module, var::String) = Core.eval(m, :(@rput($(Symbol(var)))))

end

julia> M2.f("x")
2

julia> R"x"
RObject{IntSxp}
[1] 2

julia> M2.g("x")
1

julia> R"x"
RObject{IntSxp}
[1] 1

julia> M2.g(M2, "x") # equivalent to M2.f("x")
2

julia> R"x"
RObject{IntSxp}
[1] 2
1 Like
5

Thanks @genkuroki!