error compiling roc-pg · beginners

I'm trying to use the hello-world example from the roc postgres client, but compilation gives this error

── UNKNOWN OPERATOR in src/../roc-pg/src/Pg/Client.roc ─────────────────────────

Don P (Jun 15 2025 at 08:52):

roc nightly pre-release, built from commit c47a8e9 on Sa 22 Mär 2025 09:02:05 UTC

Isaac Van Doren (Jun 15 2025 at 16:10):

That is the backpassing operator which has been removed from the language. I think roc-pg will need to be substantially refactored to be compiled again

Don P (Jun 15 2025 at 22:03):

okay thanks for the explanation. is there any sql client library available for roc?

Luke Boswell (Jun 15 2025 at 22:54):

Isaac Van Doren (Jun 15 2025 at 23:35):

Luke Boswell (Jun 15 2025 at 23:47):

Yeah, I was thinking of cross-platform libraries. The SQlite in basic-cli and basic-webserver work nice imo

Don P (Jun 16 2025 at 02:40):

I've left an issue on the roc-pg repo asking for the latest version it did compile for. It looks like the project has been idle for a year. For my purposes I can export some data from psql into sqlite for playing around with roc. thanks.

Luke Boswell (Jun 16 2025 at 02:48):

@Agus Zubiaga was instrumental with the design and evolution of the map-2 record builders, which enables a really nice API for sql clients and is much simpler than the backpassing approach or the other record builders API we have before map-2 based ones.

I'm sure he'll be keen to upgrade the package as soon as we have the new compiler online as it's a super cool API and very unique to roc. I don't know of any other language that will have as nice a story for working with sql as roc 0.1 :heart_eyes: (but I may be biased a little)

Luke Boswell (Jun 16 2025 at 02:50):

query_todos_by_status! : Str, Str => Result (List Todo) (Sqlite.SqlDecodeErr _)
query_todos_by_status! = |db_path, status|
    Sqlite.query_many!(
        {
            path: db_path,
            query: "SELECT id, task, status FROM todos WHERE status = :status;",
            bindings: [{ name: ":status", value: String(status) }],
            rows: { Sqlite.decode_record <-
                id: Sqlite.i64("id") |> Sqlite.map_value(Num.to_str),
                task: Sqlite.str("task"),
                status: Sqlite.str("status") |> Sqlite.map_value_result(decode_todo_status),
            },
        },
    )

Niclas Ahden (Jun 16 2025 at 10:02):

I posted a PR for migrating to the new syntax, but it's incomplete as I didn't touch the query builder and it may contain choices which Agus would make differently. I couldn't live without roc-pg in my life, though, so I created a fork with releases here: https://github.com/growthagent/roc-pg

I'll retire the fork once roc-pg is back in action, but it's fine to use for now if you'd like. Note that I've made some unholy changes that may or may not make it into roc-pg, like how record builders work now and I've introduced Maybe for nullable input and outputs. Here's a full example: https://github.com/growthagent/roc-pg/blob/main/examples/query-with-record-builder.roc

Agus Zubiaga (Jun 17 2025 at 03:36):

Hey all! I'm not quite back in action, but I did publish roc-pg@0.1.1 with @Niclas Ahden's migration (thx so much :heart:).

I've decided to remove the query builder from main as I never quite got it over the line, and I don't have the time to dedicate to it. I'd love to return to it when the new compiler is out, and things are calmer in my life.

Stream: beginners

Topic: error compiling roc-pg

Don P (Jun 15 2025 at 08:51):