I found that function mod2pi is not implemented yet, but mod works. Is there any list of implemented functions? Minimal working example is:

using Zygote

# This is working
gradient(x -> mod(x, 2pi), 1.)

# This is not
gradient(x -> mod2pi(x), 1.)

It will be good to analyze var_dump leftovers in project, and to add support for other functions that cause same behavior.

The program builder runs some checks to make sure that graphs are "valid":
https://github.com/ChrisCummins/ProGraML/blob/db8ae633ec02deabaa70e21b88b843dce3d05ba1/programl/graph/program_graph_builder.cc#L147-L164

These are nice for debugging, and sanity checking for graphs that we have control over, but aren't suitable for converting programs from "untrusted" sources. E.g. a compiler may choose

Currently the tests are all in folders pos and neg.

Instead, we could organize them by topic:

• syntax
• handlers
• stdlib
• ...

and add additional README.md files to the folders guiding newcomers. Additionally, the tests could have comments explaining the features.

This way we could have a low cost documentation that is automatically checked