Debugger.jl: Access object `%2`

General Usage
1

I am trying to debug some code using Debug.jl:

In _pullback(ctx, f, args) at /home/gkraemer/.julia/packages/Zygote/YeCEW/src/compiler/interface2.jl:7
  1  1 ─       $(Expr(:meta, :inline))
  2  │   %2  = (ZygoteRules._pullback)(ctx, Zygote.unwrap, :(Main.sr), Main.sr)
> 3  │   %3  = (getindex)(%2, 1)
  4  │   %4  = (getindex)(%2, 2)
  5  │   %5  = (ZygoteRules._pullback)(ctx, loss, %3)
  6  │   %6  = (getindex)(%5, 1)
  7  │   %7  = (getindex)(%5, 2)
  8  │   %8  = (tuple)(%4, %7)
  9  │   %9  = (typeof(∂(#18)))(%8)
 10  │   %10 = (tuple)(%6, %9)
 11  └──       return %10

About to run: <(getindex)((VBagg.Bags{Float64}(VBagg.Bag{Float64}[VBagg.Bag{Float64}([0.9323391769092779 0.056934747...>
1|julia> %2
ERROR: syntax: "%" is not a unary operator

I want to know how %2 looks like, because the code will fail when executing line 4. In normal code I can just press ` and get an interactive Julia prompt to explore local variables. This doesn’t work in the present case. How can I take a look at %2?

2

I am not sure Debugger.jl is set up to support this. If you can create all the arguments to _pullback, you could manually create a frame with JuliaInterpreter.enter_frame and then issue debugcommands until you’ve passed statement 2. Then you can look up the value in frame.framedata.ssavlues.

For more info, see the docs.

3

Yeah, we should add syntax in Debugger.jl for querying SSAvalues. Any suggestions?

4

Debugger seems to get the string and then do its own parsing. Could we just check for a first non-whitespace character of %?

5

I thought it would be cool to include it in the standard julia evaluation mode (which uses the Julia parser) so you could do sin(a * %2 * 5) for example but that runs into % not being an infix operator. Hmm…

1 Like
6

var"%2"? That’s what I’d try to do (as a user) first.

2 Likes
7

Yeah, that is a good idea, I’ll try it out.

8

https://github.com/JuliaDebug/JuliaInterpreter.jl/pull/395 has a PR with the var syntax:

1|debug>
In sin(x) at special/trig.jl:30
  3  │          Core.NewvarNode(:(n))
  4  │          absx = (abs)(x)
  5  │    %5  = absx
  6  │    %6  = ($(Expr(:static_parameter, 1)))(π)
> 7  │    %7  = (/)(%6, 4)
  8  │    %8  = (<)(%5, %7)
  9  └───       goto #6 if not %8
 10  2 ── %10 = absx
 11  │    %11 = (eps)($(Expr(:static_parameter, 1)))

About to run: (/)(3.141592653589793, 4)
1|julia> var"%5", var"%6"
(2.0, 3.141592653589793)
6 Likes