Returning multiple rows in materialized mode inside the extension

Hi,

I represent a small group of developers. We are working on an open-source
PostgreSQL extension to enable processing of genomic data inside Postgres.
We have an extensive knowledge of molecular biology or data science and
none of the Postgres internals.

I don’t know if this mailing list is a good place to ask this question, but
if it’s not, just correct me.

*The problem:*

We currently have a one-to-many function (an operation that produces
multiple rows per one one input row). Now we would like to translate that
functionality to a sensible many-to-many. We need to know how we are
constrained by the internals of Postgres itself and what syntax we should
use.

Also, the operation we are implementing requires knowing the full set of
inputs before it can be computed.

*Current solution:*

There is ValuePerCall (1/0 returned rows) or Materialize mode (any number
of returned rows), however the second one does not offer any invocation
counter (like ValuePerCall does). Hence to provide any persistence between
subcalls we introduced the following syntax:

*SELECT _ FROM table t, my_function(t.a, t.b, t.c, number_of_rows);*

Where by FROM a, b we mean cartesian product a times b. And my_function for
first (number_of_rows - 1) invocations returns an empty set and the full
result set for the last one.

Sadly this syntax requires us to enter a number of rows which is not very
convenient.

Do you know how to handle this situation correctly? We looked for example
at the code of tablefunc but the syntax there requires a full SQL query as
an input, so that wasn’t useful.