Prelude OCaml


This module builds on top of the shared Programming module.


Prelude provides powerful out-of-the-box experience for programming in OCaml:

  • major-mode for editing OCaml code (tuareg-mode)
  • integration with utop, OCaml's modern top-level (you can think of it as a REPL)
  • linting via flycheck or merlin
  • code completion via merlin

You can get similar experience using OCaml's LSP server, but it's based on Merlin internally and the setup with LSP is a bit more involved.


When the prelude-ocaml is enabled it will install 3 packages:

  • tuareg-mode
  • utop
  • merlin
  • flycheck-ocaml

Environment Setup

These setups for ocaml assume that you are using the OPAM package manager (

Because of the apparent complexity of getting Emacs environment variables setup to use opam correctly, it is instead easier to use opam itself to execute any necessary commands.

Also, the standard OCaml toplevel usage has been replaced in favor of UTOP, the universal toplevel, and we assume that you are using the Jane Street Core libraries rather than the regular OCaml standard libraries

The minimum required setup for using Prelude's OCaml setup would be to install OPAM, and then, minimally `opam install core utop'. A good getting started guide is available at


Prelude disables Merlin's own linting in favor of Flycheck. It also leverages Merlin's company-mode backend instead of using directly Merlin's rudimentary auto-completion system.