Support backpropagation through unfold and recurse

Description

Contributor guide

Tech stack

None

Domain

machine learning

Issue type

feature

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

5

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

over 1 week

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

stale

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

mostly clear

Prerequisites

Julia knowledgeProbabilistic programming basicsBackpropagation understandingGen.jl codebase familiarity

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

15

Research direction

The issue requires implementing backpropagation through the 'unfold' and 'recurse' functions in Gen.jl. The specific lines are in src/modeling library/unfold/unfold.jl around line 40-41 and src/modeling library/recurse/recurse.jl around line 130-131. A contributor should first understand how backpropagation is implemented for other functions in the codebase. The issue has been open since 2019 with no recent activity, so it is advisable to re engage with maintainers to clarify expected behavior and ensure the feature is still desired.