Install

You need opam, OCaml’s package manager, and OCaml 5.5 or later. wiretype 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

wiretype 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 wiretype ocaml-base-compiler
eval $(opam env)

3. Install wiretype

opam repo add hypha https://github.com/hyphatech/opam-repository.git
opam install wiretype ppx_wiretype

Package	What it is
wiretype	descriptions: reading, writing, bounds, kinds, schemas; links Ptime, Mtime and Uuidm alone
ppx_wiretype	[@@deriving wiretype], which writes a type’s description

A program that only writes its descriptions by hand needs wiretype alone.

4. Name it in dune

A program names the libraries it uses in its dune file, and the deriver as a preprocessor:

(executable
 (name main)
 (libraries wiretype)
 (preprocess (pps ppx_wiretype)))

A description that names a time or a UUID – a Ptime.t, an Mtime.Span.t or a Uuidm.t – needs that library in libraries too: ptime, mtime or uuidm.

Check it worked

$ ocaml -version
$ opam list wiretype ppx_wiretype

The first says 5.5 or later. The second lists both packages 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 writes a first description, next.