Newbie problem: "Error: Unbound module" with Petrol

I’m new to OCaml and interested in using Petrol to interact with an sqlite3 database. To start things out, I’m trying to run the first example in the Petrol readme.md. In particular, I want to build the code:

open Petrol
open Petrol.Sqlite3

(* define a new schema *)
let schema = StaticSchema.init ()

(* declare a table *)
let example_table, Expr.[name; age] =
StaticSchema.declare_table schema ~name:“example”
Schema.[
field “name” ~ty:Type.text;
field “age” ~ty:Type.int
]

which I put in the file test1.ml.

First, I install Petrol with:

opam install petrol

I have a dune file which contains

(executable
(name test1)
(libraries petrol))

When I run

dune build test1.exe

I get the error:

File “test1.ml”, line 2, characters 5-19:
2 | open Petrol.Sqlite3
^^^^^^^^^^^^^^
Error: Unbound module Petrol.Sqlite3

So it appears that the line for

open Petrol

worked fine, but it didn’t know how to find Petrol.Sqlite3 which is opened in the next line.

I’ve tried to do

opam install petrol.sqlite3

and

opam install petrol.Sqlite3

which don’t work because it returns an error, “Package petrol has no version sqlite3.” or “Package petrol has no version Sqlite3.”

I tried modifying the dune file to

(executable
(name test1)
(libraries petrol petrol.sqlite3))

(and the same modification with a capital S for Sqlite3) but I get “Error: Library “petrol.sqlite3” not found.” or “Error: Library “petrol.Sqlite3” not found.”

I’m not sure where to go from here to get this working. Any help would be appreciated!

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