Introduction to Rebugger

Rebugger is an expression-level debugger for Julia. It has no ability to interact with or manipulate call stacks (see ASTInterpreter2), but it can trace execution via the manipulation of Julia expressions.

The name "Rebugger" has 3 meanings:

• it is a REPL-based debugger (more on that below)
• it is the Revise-based debugger
• it supports repeated-execution "surface" debugging

Rebugger is an unusual debugger with a novel work-flow paradigm. With most debuggers, you enter some special mode that lets the user "dive into the code," but what you are allowed to do while in this special mode may be limited. In contrast, Rebugger brings the code along with its input arguments to the user, presenting them both for inspection, analysis, and editing in the (mostly) normal Julia interactive command line. As a consequence, you can:

• test different modifications to the code or arguments without being forced to exit debug mode and save your file
• run the same chosen block of code repeatedly (perhaps with different modifications each time) without having to repeat any of the "setup" work that might have been necessary to get to some deeply nested method in the original call stack. In other words, Rebugger brings "internal" methods to the surface.
• run any desired command that helps you understand the nature of a bug. For example, if you've already loaded MyFavoritePlottingPackage in your session, then when debugging you can (transiently) add Main.MyFavoritePlottingPackage.plot(x, y) as a line of the method-body you are currently analyzing, and you should see a plot of the requested variables.

Rebugger exploits the Julia REPL's history capabilities to simulate the stacktrace-navigation features of graphical debuggers. Thus Rebugger offers a command-line experience that is more closely aligned with graphical debuggers than the traditional s, n, up, c commands of a console debugger.

Installation and configuration

Begin with

(v1.0) pkg> add Rebugger

You can experiment with Rebugger with just

julia> using Rebugger

If you decide you like it (see Usage), you can optionally configure it so that it is always available (see Configuration).