Understanding `*Bindings` in `JuliaLowering.jl`

General Usage
1

Hi everyone! I am trying to understand the building pieces of JuliaLowering.jl. I am very new to compilers so I apologise in advance if my questions have very obvious answers.

I don’t understand the behaviour of Bindings in the contexts created at each lowering step. Starting from this script I have a bunch of questions:

text = """
x::Int = 10
"""

in_mod = Module()
ex = parseall(JuliaLowering.SyntaxTree, text)

ctx1, ex_macroexpand = JuliaLowering.expand_forms_1(in_mod, ex)
ctx2, ex_desugar = JuliaLowering.expand_forms_2(ctx1, ex_macroexpand)
ctx3, ex_scoped = JuliaLowering.resolve_scopes(ctx2, ex_desugar)
ctx4, ex_converted = JuliaLowering.convert_closures(ctx3, ex_scoped)
ctx5, ex_compiled = JuliaLowering.linearize_ir(ctx4, ex_converted)

  1. Should I expect ctx* to have a BindingInfo for x? I thought yes, but there is none. Why is that?

  2. While there’s no binding for x, there is a binding for the return value (I think?), return_tmp: JuliaLowering.BindingInfo(1, "return_tmp", :local, 26, nothing, nothing, 0, false, true, false, true, true, false, false). This only appears in the linearize_ir step, but it seems that the other contexts are modified as well after each pass (ctx1 doesn’t have that binding after running expand_forms_1 but it does have it after running linearize_ir). What is the advantage of not having the contexts independent from each other?

  3. What is the (theoretical) difference between a lambda binding and a closure binding? My understanding is that lambda bindings are bindings for lambda functions parameters (x = 2 is a lambda binding in the context of the function x -> x + 3 being called with the argument 2), while closure bindings are bindings for variables captured by a closure (y = 1 is a closure binding in the context of the function f(x) = x + y with y defined somewhere above and it has the value 1 assigned to it). Is this correct? Does the concept of “binding” refer to a name → value association in a particular context, or does it describe something more complex? (For example, is the closure binding the association from y to 1 in the context of the function f(x) = x + y with y = 1, or is it the entire closure, or something different?)

  4. Could you maybe point me somewhere I can find some explanations as to how the syntax graph changes from pass to pass? It is quite difficult for me to see this from the source code and I also can’t seem to come up with clarifying examples.

For using the package I followed the instructions in the README.

julia> versioninfo()
Julia Version 1.12.0-DEV.631
Commit a4e793ee31* (2024-05-30 19:25 UTC)
Platform Info:
  OS: macOS (arm64-apple-darwin24.3.0)
  CPU: 8 × Apple M1
  WORD_SIZE: 64
  LLVM: libLLVM-17.0.6 (ORCJIT, apple-m1)
Threads: 1 default, 0 interactive, 1 GC (on 4 virtual cores)