Provides support for the F# language in Emacs. Includes the following features:

• Syntax highlighting and indentation
• Support for F# Interactive
• Via Eglot LSP-client integration:
  • Displays type signatures and tooltips
  • Flymake
  • Completion
  • Jump to definition Find Identifier References (Xref)

The current version of fsharp-mode installs fsautocomplete.exe automatically via eglot-fsharp.el (part of this mono repo, eglot-fsharp on melpa) or lsp-mode (untested).

fsharp-mode is tested with Emacs 27.1+ and NET Core 6 (LTS)

fsharp-mode is available on MELPA and can be installed using the built-in package manager.

If you’re not already using MELPA, add the following to your init.el:

;;; Initialize MELPA
(require 'package)
(add-to-list 'package-archives '("melpa" . "http://melpa.org/packages/"))
(unless package-archive-contents (package-refresh-contents))
(package-initialize)

;;; Install fsharp-mode
(unless (package-installed-p 'fsharp-mode)
  (package-install 'fsharp-mode))

(require 'fsharp-mode)

If you are a user of use-package you can instead do

(use-package fsharp-mode
  :defer t
  :ensure t)

I recommend to use Cask. Add this to your Cask file:

(depends-on "fsharp-mode" :git "https://github.com/fsharp/emacs-fsharp-mode.git")

The eglot-fsharp integration is not part of fsharp-mode on melpa.

It is available via the seperate package eglot-fsharp on melpa.

Add to your config:

(require 'eglot-fsharp)

and execute M-x eglot

With eglot running use `xref-find-definitions` (bound to M-. pr. default) to go to definition. Completions are accessable via. `completion-at-point` (or a completion backend ex. company-mode https://melpa.org/#/company)

fsharp-mode has support for Emacs build-in project management via project.el

The F# compiler and interpreter should be set to good defaults for your OS as long as the relevant executables can be found on your PATH or in other standard locations. If you have a non-standard setup you may need to configure these paths manually.

On Windows:

(setq inferior-fsharp-program "c:\\Path\\To\\Fsi.exe")

On Unix-like systems, you must use the –readline- flag to ensure F# Interactive will work correctly with Emacs. Typically fsi and fsc are invoked through the shell scripts fsharpi and fsharpc:

(setq inferior-fsharp-program "path/to/fsharpi --readline-")

If you are new to Emacs, you might want to use the menu (call menu-bar-mode if you don’t see it). However, it’s usually faster to learn a few useful bindings:

To interrupt the interactive mode, use C-c C-c. This is useful if your code does an infinite loop or a very long computation.

If you want to shift the region by 2 spaces, use: M-2 C-c r

In the interactive buffer, use ==M-RET= to send the code without explicitly adding the ;; thing.

In order to change tab size it is possible to put this in emacs profile:

(setq-default fsharp-indent-offset 2)

Because the F# language is sensitive to indentation, you might wan’t to highlight indentation:

(add-hook 'fsharp-mode-hook 'highlight-indentation-mode)

fsharp-mode is still under development, so you may encounter some issues. Please report them so we can improve things! Open an issue on Github.

The root cause is documented in this Ionide issue: 4.2.0 - No auto complete or typechecking in FSX files

As a workaround can add a reference to the facade netstandard assembly (path is platform/SDK-dependent).

On Arch Linux using dotnet sdk lts add this to your fsx file:

#r "/opt/dotnet/sdk/2.1.801/ref/netstandard.dll"

If your project file does not seem to be being parsed correctly, so that you have missing references or other incorrect intellisense results, it is possible to obtain a detailed log of LSP events in this buffers:

• *EGLOT (PROJECT/fsharp-mode) stderr*
• *EGLOT (PROJECT/fsharp-mode) output*
• *EGLOT (PROJECT/fsharp-mode) events*

This project is maintained by the F# Software Foundation, with the repository hosted on GitHub.

Pull requests are welcome. Please run the test-suite with make test before submitting a pull request.

The maintainers of this repository appointed by the F# Core Engineering Group are:

• Jürgen Hötzel, Steffen Forkmann, Karl Nilsson and Guillermo López-Anglada
• The primary maintainer for this repository is Jürgen Hötzel

Previous maintainers:

• Robin Neatherway