You’re seeing what’s called lowered code, which is what happens when Debugger can’t find the source of what you’re debugging. Not sure why this is happening, with Julia 1.1 I get this:
julia> @enter foo(3)
In foo(n) at /tmp/rundebug.jl:4
3 function foo(n)
>4 x = n+1
5 ((BigInt[1 1; 1 0])^x)[2,1]
which I suspect is more what you were hoping to see.
Since I can’t replicate what you’re seeing, I don’t know exactly why it’s happening. One thought is that perhaps you might have more luck if you put your code in a file, save it, and then in the Julia session say
and then start debugging.
But I second the recommendation to use Juno’s debugger. Instructions are here.