idris-mode for emacs

This is an emacs mode for editing Idris code.

This mode was original designed to work with version 1 of the language through an IDE-Protocol. Idris2 uses the next iteration of the same protocol. Idris-mode tries to maintain compatibility with both protocol versions, however, not all the features from the IDE-Protocol have been realised in Idris2. When using idris-mode with Idris2 your experience might be a bit clunky.

PRs to both projects to get things working smoothly are more than welcome!

Note on Syntax Highlighting.

Syntax highlighting functional languages is a little quirky; I've deferred to haskell-mode for some things (e.g. font-lock-variable-name-face for operators) and done some other things as appropriate for Idris. font-lock-type-face isn't used at all, for example, and data types declared with data use the same face as functions and values defined with =.

Changes

See the file CHANGES.markdown in the repository root for user-visible changes between versions, starting at version 0.9.18.

Documentation

There are some docstrings spread around the mode, thus C-h m is helpful and returns the available key bindings. The REPL also supports tab completion, thus pressing tab opens a buffer with the available completions.

The extended abstract for DTP14 gives overview of the features of idris-mode. The underlying protocol is described in the Idris documentation.

Certain areas of idris-mode show explanatory help text. When you've learned how to use idris-mode, you can turn these off by setting idris-show-help-text to nil.

Inferior Idris

There is now support for running an Idris interpreter in a buffer. Use C-c C-l to load the current Idris buffer into the interpreter. This will spawn an inferior Idris process and load the buffer. It will report warnings if idris reports any. Pressing C-c C-l again will reload that buffer - if you switch to a different buffer and press C-c C-l, that buffer will be loaded instead.

Customize idris-interpreter-path if Idris is not on your default path.

Highlighting

idris-mode provides two forms of source code highlighting, that work together: conventional Emacs font-lock to highlight things like keywords and code that has not yet been type checked, and compiler-supported semantic highlighting of identifiers (as known from Agda). Semantic highlighting is controlled by the variable idris-semantic-source-highlighting.

Keybindings

idris-mode follows conventions from SLIME whenever possible. In particular:

• For ease of typing, any sequence of three keys allows the final key to be pressed with or without the control key, unless the last key is h. For example, C-c C-d d can also be typed C-c C-d C-d.
• Documentation-related commands are prefixed with C-c C-d.
• Commands related to building packages are prefixed with C-c C-b.

Contextual menus

idris-mode makes use of semantic information from the Idris compiler to display contextual menus. By default, the graphical contextual menu is bound to the right mouse button and the textual contextual menu is bound to C-c C-SPC. Using these commands will display commands that are available based on what is under the mouse pointer or what is at point, respectively.

Error messages

When loading a buffer, idris-mode will decorate errors from the Idris compiler with underlines. Tooltips show the error message. The following error message commands are available:

• M-n: Move the point to the next compiler note
• M-p: Move the point to the previous compiler note

Colors and fonts

Idris mode displays output from the Idris compiler with full semantic highlighting. It is quite possible that this is ugly in your color scheme. If that is the case, you can use M-x customize-group RET idris-faces RET to modify them. In particular, some users don't like the background color for the currently loaded region of the buffer. This is controlled by idris-loaded-region-face. Remove all its properties to make it disappear.

Interactive editing

The following commands are available when there is an inferior Idris process (which is started on demand by the commands):

• C-c C-l: Load the current file into Idris. A prefix argument causes Idris to only load the portion of the file up to point.
• C-u C-u C-c C-l: Obliterate the loading marker, switching back to loading the whole buffer.
• C-c C-n, C-c C-p: Extend and contract the region to be loaded, if such a region exists, one line at a time.
• C-c C-s: Create an initial pattern match clause for a type declaration
• C-c C-m: Add missing pattern-match cases to an existing definition
• C-c C-a: Attempt to solve a hole automatically. A plain prefix argument prompts for hints, while a numeric prefix argument sets the recursion depth.
• C-c C-S-a: (Idris 2 only) Replace the previous proof search answer with a different attempt by the compiler. If no further attempts are available it leaves the last one unchanged.
• C-c C-e: Extract a hole or provisional definition name to an explicit top level definition
• C-c C-c: Case split the pattern variable under point, or fill the hole at point with a case expression.
• C-c C-t: Get the type for the identifier under point. A prefix argument prompts for the name.
• C-c C-w: Add a with block for the pattern-match clause under point
• C-c C-h a: Search names, types, and docstrings for a given string.
• C-c C-z: Pop to a presently open REPL buffer or to last Idris code buffer if invoked in REPL buffer.

Online documentation

The Idris compiler supports documentation. The following commands access it:

• C-c C-d d: Show the documentation for the name under point (:doc at the REPL). A prefix argument prompts for the name.
• C-c C-d a: Search the documentation for a string (:apropos at the REPL).
• C-c C-d t: Search for documentation regarding a particular type (:search at the REPL).

Additionally, idris-mode integrates with eldoc-mode, which shows documentation overviews and type signatures in the minibuffer. (Eldoc support is yet to be implemented in the Idris2.)

Completion

M-Tab or whatever you have completion-at-point bound to will ask the running Idris process for completions for the current identifier. Note that this command requires that the Idris interpreter is already running, because attempting to load an incomplete buffer would probably not work.

Active terms

Some terms output by the Idris compiler are active, meaning that idris-mode is aware of their original representation. For these terms, commands exist to normalise them and show or hide their implicit arguments.

To see the active terms available, use the command idris-add-term-widgets, which is also found in the menu. To issue term commands, right-click on the triangle that points at the term. The widgets can be removed again using idris-remove-term-widgets.

The following keybindings are available:

• C-c C-m n: Normalize the term at point (M-x idris-normalize-term)
• C-c C-m i: Show implicits for the term at point (M-x idris-show-term-implicits)
• C-c C-m h: Hide implicits for the term at point (M-x idris-hide-term-implicits)
• C-c C-m c: Show the core language for the term at point (M-x idris-show-core-term)

Package files

Idris's build system, which consists of package files ending in .ipkg, has rudimentary support from idris-mode. The following commands are available in Idris buffers or package buffers; if they are run from an Idris buffer, then idris-mode will attempt to locate the package file automatically. The mnemonic for C-b in the prefix is "build".

• C-c C-b c: Clean the package, removing .ibc files
• C-c C-b b: Build the package
• C-c C-b i: Install the package to the user's repository, building first if necessary

The following commands are available in idris-ipkg-mode:

• C-c C-f: Insert a field, with completion support. Completion for field names is also available by pressing M-TAB.

When a package is present, idris-mode gains a few convenience features. In particular, the Idris compiler's working directory is set based on the sourcedir directive in the package file, and certain filenames or module names become clickable buttons, to conveniently open them.

Additionally, the command M-x idris-start-project will create a directory structure and initial package file for a new project.

Using packages

idris-mode supports setting the packages to be loaded by the Idris process. Specifically, the buffer-local variable idris-load-packages is expected to contain a list of package names to be loaded. When the buffer is loaded, if the current packages loaded by the Idris process don't agree with the contents of the variable, Idris is restarted with the correct -p options.

You can set this variable interactively using the command M-x idris-set-idris-load-packages. This will add the variable as a file-local variable, so that it will be set automatically when the file is loaded in the future.

Installation

Idris mode uses lexical binding and other features not available in versions of Emacs prior to 24. Thus, only Emacs 24 and up are supported.

You can install pre-built packages from MELPA or MELPA Stable: idris-mode will automatically be enabled in .idr files without any further configuration. Please install a version corresponding to the version of Idris that you use. The current Git (and therefore MELPA) version of idris-mode will work with the current Git version of Idris, while the latest release on Hackage will work with the corresponding tagged version of idris-mode.

If you are using Emacs 24.4 or newer with released versions of Idris, but you want other packages from MELPA, then you can pin the version of idris-mode to the one found in MELPA Stable. For details, please consult the documentation for package-pinned-packages (C-h v package-pinned-packages RET).

Alternatively, download the elisp files, and place them somewhere in your load path. If you're installing manually, then you also need to install the prop-menu package, which idris-mode uses to create contextual menus. Installation from MELPA will automatically install dependencies.

If you want idris-mode to be enabled by default, add the line (require 'idris-mode) to your ~/.emacs or ~/.emacs.d/init.el file.

Idris mode is heavily dependent on the Idris compiler for its more advanced features. Thus, please ensure that Emacs can see your Idris binary. Emacs looks for executables in the directories specified in the variable exec-path, which is initialized from your PATH at startup. If Idris is not on your PATH, then you may need to add it to exec-path manually. E.g.: if you installed idris with cabal into ~/.cabal/bin, then add the line (add-to-list 'exec-path "~/.cabal/bin") to your emacs initialization file. Alternatively, you can customize the variable idris-interpreter-path and provide an absolute path.

Example of installation and setup for Idris2 with use-package package from MELPA.

(use-package idris-mode
  :ensure t

  :custom
  (idris-interpreter-path "idris2"))

Example of installation and setup for Idris2 with use-package package directly from source.

(use-package idris-mode
  :init (require 'idris-mode)
  :load-path "path-to/idris-mode/root/source-code-directory/relative-to-current-file"

  :custom
  (idris-interpreter-path "idris2"))

Customization

Customize various aspects of the mode using M-x customize-group RET idris RET.

Additionally, you may want to update your Emacs configuration so that it does not open Idris bytecode files by default. You can do this by adding ".ibc" to the variable completion-ignored-extensions, either in customize or by adding (add-to-list 'completion-ignored-extensions ".ibc") to your init.el. If you use ido, then you may also need to set ido-ignore-extensions to t.

Keybinding conventions

All three-letter keybindings are available in versions with and without C- on the final key, following the convention from SLIME.

Integration with other Emacs packages

Evil mode support (Vim compatibility)

There is emulation for idris-vim commands in idris-mode. To enable this support please install the evil and evil-leader packages from MELPA (or your favorite source of packages) and then add (idris-define-evil-keys) to init.el.

The following commands are supported (taken from idris-vim):

• <LocalLeader>r: Reload file

• <LocalLeader>t: Show type

• <LocalLeader>d: Add initial pattern-match clause

• <LocalLeader>c: Case split

• <LocalLeader>w: Add with clause

• <LocalLeader>m: Add missing pattern-match cases

• <LocalLeader>p: Proof search

• <LocalLeader>h: Show documentation

Helm

helm-idris builds on idris-mode to provide an alternative interface to looking up documentation. It supports incremental searching in documentation and names, similar to the built-in :apropos and idris-apropos commands.

Pop Win

Pop Win is an Emacs utility to manage ephemeral buffers, such as completion and compilation buffers. It provides tools for controlling their position and lifetime. Pop Win requires configuration to work with idris-mode. An incomplete example configuration follows:

(push 'idris-compiler-notes-mode
      popwin:special-display-config)
(push '(idris-repl-mode
        :height 0.2
        :noselect nil
        :position bottom
        :stick t)
      popwin:special-display-config)

Spacemacs

We have received reports that the idris-stay-in-current-window-on-compiler-error setting does not function properly for users of Spacemacs. The following user configuration can fix it:

(defun dotspacemacs/user-config ()
  ; ...
  (with-eval-after-load 'idris-mode
    (setq idris-stay-in-current-window-on-compiler-error t)
    (dolist (x '("*idris-notes*" "*idris-holes*" "*idris-info*"))
      (plist-put (cdr (assoc x popwin:special-display-config)) :noselect t))))

frames-only-mode and many buffer pop-ups

frames-only-mode obviates the need for emacs internal windows so that emacs can get along better with tiling managers - such as xmonad - by using emacs' frames instead of windows.

Throughout a session with idris-mode, many frames will accumulate, such as *idris-holes*, and over time these clutter your screen. A quick simple solution is to add the following to your emacs configuration:

(defun my-idris-mode-hook ()

  ;; This makes it so that especially errors reuse their frames
  ;; https://emacs.stackexchange.com/questions/327/how-can-i-block-a-frame-from-being-split/338
  ;; alternatively, add this to certain frames: (set-frame-parameter nil 'unsplittable t)
  ;; (without this, Idris throws out tons of new frames)
  (add-to-list 'display-buffer-alist
               '(".*". (display-buffer-reuse-window . ((reusable-frames . t)))))
  (setq idris-stay-in-current-window-on-compiler-error t)
  (setq idris-prover-restore-window-configuration t)

  ;; If you kill a buffer (eg, hit "q"), frames with these names wil also be killed
  (add-to-list 'frames-only-mode-kill-frame-when-buffer-killed-buffer-list "*idris-repl*")
  (add-to-list 'frames-only-mode-kill-frame-when-buffer-killed-buffer-list "*idris-notes*")
  (add-to-list 'frames-only-mode-kill-frame-when-buffer-killed-buffer-list "*idris-info*")
  (add-to-list 'frames-only-mode-kill-frame-when-buffer-killed-buffer-list "*idris-holes*"))

(add-hook 'idris-mode-hook #'my-idris-mode-hook)

Flycheck (asynchronous syntax checks in buffer)

To enable on-the-fly syntax checking of Idris code using flycheck add these lines to your configuration:

(require 'flycheck-idris)
(add-hook 'idris-mode-hook #'flycheck-mode)

Example using use-package package:

(use-package idris-mode
  :ensure t

  :config
  (require 'flycheck-idris) ;; Syntax checker
  (add-hook 'idris-mode-hook #'flycheck-mode))

Xref (Cross-referencing commands)

Jump to definitions xref-find-definitions (M-.) in current file or project is supported as long as Idris compiler returns file path to the definition. To support jump to definitions for which Idris could not find relevant source file you may want customise idris-xref-idris-source-location and idris-xref-idris-source-locations. You can do that interactively using M-x customize-group [enter] -> idris-xref [enter] command or programatically. Example using use-package package.

(use-package idris-mode
  :ensure t ;; Installing from (M)ELPA

  :custom
  (idris-interpreter-path "idris2")

  ;; Assuming you did `git clone git@github.com:idris-lang/Idris2.git ~/sources/idris2`
  (idris-xref-idris-source-location "~/sources/idris2")
  ;; Paths to random additional idris packages you may be using
  (idris-xref-idris-source-locations '("~/sources/idris-ncurses/src"
                                       "~/sources/idris-foo/src")))

Hideshow Minor Mode (hs-minor-mode)

If you have enabled hs-minor-mode globally you may want to disable it for Idris prover buffers as it may cause errors in some situations (When invoking idris-quit command for example). Example of enabling hs-minor-mode for all buffers derived from prog-mode except the idris-prover buffers.

(add-hook 'prog-mode-hook
          #'(lambda ()
              (if (derived-mode-p 'idris-prover-script-mode)
                  (hs-minor-mode -1)
                (hs-minor-mode))))