A Julia debugger, with support for breakpoints, trapping errors, and inspection of local variables, has been long desired in the Julia community. We describe an approach based on a new interpreter for Julia code, JuliaInterpreter.jl. JuliaInterpreter is able to evaluate Julia’s lowered representation statement-by-statement, and thus serves as the foundation for inspecting and manipulating intermediate results. Compared with previous tools, JuliaInterpreter offers several new features, such as improved performance, the ability to evaluate top-level code, built-in support for breakpoints, and the ability to switch flexibly between compiled and interpreted evaluation. JuliaInterpreter can be used directly as a standalone interpreter, and this makes it interesting for other purposes such as exploring tradeoffs between compile-time and run-time efficiency.

To enable JuliaInterpreter’s use as a debugger, we developed three different front-ends. One is the Juno IDE, which supports graphical management of breakpoints and stepping through code in a manner integrated with its editing capabilities. In addition to Juno, there are two different console-based (REPL) interfaces. Debugger.jl offers the most powerful control over stepping, whereas Rebugger.jl emulates features of a graphical client. We will demonstrate these tools as means to access some of JuliaInterpreter’s capabilities.