utop

Start utop REPL

$ utop

$ utop -init [file.ml]

$ utop -require [lwt]

$ utop -e "[print_endline \"Hello\"]"

$ utop -no-init

utop [options] [file]

utop is an enhanced toplevel (REPL) for OCaml with features including real-time context-sensitive completion, syntax highlighting, history, and support for multiple editing modes.
The completion bar displays possible completions as you type and updates dynamically. Navigate completions with Alt-Left/Right and select with Alt-Down. The interface supports multiline input without requiring explicit line continuation.
utop integrates with Emacs using the Tuareg, caml, and ReasonML modes. From Emacs, use M-x utop to start a session with additional key bindings for evaluating code from buffers.

-init file

Load specified file on startup.

Require specified findlib package.

Evaluate expression and exit.

Skip loading initialization files.

Run in Emacs mode.

Read input from standard input.

Display help.

#help: Show available commands.
#quit or Ctrl-D: Exit utop.
#use file: Load file into the session.
#require package: Load findlib package.
#list: List loaded modules.
#utop_bindings: Show key bindings.

~/.config/utop/init.ml: Initialization script.
~/.utoprc: Configuration file for colors and settings.
~/.ocamlinit: Alternative initialization (also used by standard ocaml).

Requires OCaml installation. Some features need findlib. Emacs integration requires mode setup. Heavy packages may slow startup.

utop was created as a modern replacement for the standard OCaml toplevel, providing a significantly improved user experience with completion, history, and editor integration. It's maintained by the OCaml community and has become the recommended REPL for OCaml development.

ocaml(1), ocamlfind(1), opam(1)