Install

You need opam, OCaml’s package manager, OCaml 5.5 or later, and a Postgres server to connect to. postgres-eio brings dune, the build tool, with it.

1. Install opam

macOS

brew install opam

Linux

bash -c "sh <(curl -fsSL https://opam.ocaml.org/install.sh)"

Windows

winget install Git.Git OCaml.opam

postgres-eio should work on Windows, but it is not tested there. If something fails, WSL gives you a Linux to follow the Linux steps in.

2. Set up OCaml

opam init

Answer yes when it offers to set up your shell. This installs the latest OCaml, which takes a few minutes. Then let this terminal see it – a new terminal does by itself:

macOS and Linux

eval $(opam env)

Windows

(& opam env) -split '\r?\n' | ForEach-Object { Invoke-Expression $_ }

Already had opam?

Check ocaml -version. If it is older than 5.5, make a switch – an environment of its own – with the latest OCaml:

opam switch create postgres-eio ocaml-base-compiler
eval $(opam env)

3. Install postgres-eio

opam repo add hypha https://github.com/hyphatech/opam-repository.git
opam install postgres-eio

This installs the driver and everything it needs. A program runs it inside Eio’s event loop, which eio_main starts, so install that beside it:

opam install eio_main

A program names both in its dune file:

(libraries postgres-eio eio_main)

Check it worked

$ ocaml -version
The OCaml toplevel, version 5.5.1

$ opam list postgres-eio

It lists postgres-eio with a version, not --, under Installed.

Your editor

For completion, types on hover and errors as you type, install the language server, then the OCaml Platform extension in VS Code – or the OCaml support of your editor:

opam install ocaml-lsp-server

The quick start connects and runs a query, next.