In a Jupyter notebook running the Julia 0.6.4 kernel, typing a leading question mark(?) followed by anything results in similar problems for me, on Mac and Linux:
?+
UndefVarError: result not defined
Stacktrace:
[1] execute_request(::ZMQ.Socket, ::IJulia.Msg) at /Users/E19983/.julia/v0.6/IJulia/src/execute_request.jl:186
[2] (::Compat.#inner#14{Array{Any,1},IJulia.#execute_request,Tuple{ZMQ.Socket,IJulia.Msg}})() at /Users/E19983/.julia/v0.6/Compat/src/Compat.jl:332
[3] eventloop(::ZMQ.Socket) at /Users/E19983/.julia/v0.6/IJulia/src/eventloop.jl:8
[4] (::IJulia.##15#18)() at ./task.jl:335
It works fine when running julia from the terminal instead of inside a Jupyter notebook.
The updated version of IJulia (which includes that fix) has been tagged, but it hasn’t yet been merged into the Julia package listing: https://github.com/JuliaLang/METADATA.jl/pull/16025 . It will probably be available through Pkg.update() within a day or two.
If you want to get the latest version of IJulia right now, you can check out the master branch of IJulia with:
Pkg.checkout("IJulia")
to undo that and go back to the released version, do Pkg.free("IJulia").