rtpsw

> What is expected for this repo? a merge commit or a rebase? @cpcloud ?

I'm confused about what the next steps here are and who would be taking them. @cpcloud ?

This is for embedding vector UDF implementations - using the [`func` member](https://github.com/ibis-project/ibis/blob/82429de7b77acf531157cd4b149c889a32ce7df1/ibis/expr/operations/vectorized.py#L14). See [`test_udf.py` in Arrow](https://github.com/apache/arrow/blob/50fb5b0df84a3ccaa665965e36a6e757d1af98f1/python/pyarrow/tests/test_udf.py) for the scalar (rather than vector) UDF is currently implemented in a Substrait consumer....

AFAIK, we ended up solving this using a [`NamedTapRel` extension](https://github.com/apache/arrow/blob/45918a90a6ca1cf3fd67c256a7d6a240249e555a/cpp/proto/substrait/extension_rels.proto#L48-L60), i.e., outside the scope of Substrait itself. I think this can be closed. @icexelloss?