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Polywell Manual

Polywell is at its core a library for creating programmable textual and graphical interfaces where keystrokes are bound to functions and operate on buffers.

It also ships with some code which uses this functionality to construct a text editor and repl, (in the config dir) but you can just as well replace those bits with your own code or define a new mode which defines a simulated SSH client or platformer level editor.

Polywell is in the process of being ported from Lua to Fennel and still has some significant Lua parts, but the API uses kebab-case for its function names.


Polywell has a bunch of handlers which need to be wired into the love table; usually in your love.load function:

(set love.keyreleased polywell.handlers.keyreleased)
(set love.keypressed polywell.handlers.keypressed)
(set love.textinput polywell.handlers.textinput)

-- if you want polywell to handle mouse events too:
(set love.wheelmoved polywell.handlers.wheelmoved)
(set love.mousepressed polywell.handlers.mousepressed)
(set love.mousereleased polywell.handlers.mousereleased)
(set love.mousemoved polywell.handlers.mousemoved)
(set love.mousefocus polywell.handlers.mousefocus)

But of course you can set the love handlers to your own functions which can intercept events before they are sent to the Polywell handlers too:

(fn love.keypressed [key]
  (if (= key "escape")
    (polywell.handle_key key)))

You also will need to either set love.draw to polywell.draw or call polywell.draw from within your own drawing function.

Your love.load function will probably want to call love.graphics.setFont, love.keyboard.setTextInput, and love.keyboard.setKeyRepeat, and you will also want to load the config to create modes and key bindings: (require :config).

Whatever config gets loaded is responsible for initializing the editor at some point by calling the polywell.init function, which takes an buffer name, mode, and list of strings to populate the initial buffer with. You can pass a final fs arg representing the filesystem if you want to use Polywell with a simulated in-game filesystem instead of the actual system disk.

The polywell module contains the public API for Polywell; other modules are internal and shouldn't be used from external code.

Buffers and Modes

Every file you open in Polywell has a buffer associated with it, and you can also have buffers like *repl* which aren't backed by a file at all. You can use the polywell.open function to open a new buffer. It takes the file's path as the first argument and a mode as the second argument, but you can omit the mode if you want polywell to figure out the mode for itself. If you are making a buffer like *repl* which doesn't correspond to a file, pass true as the third argument, and use a path which has * around the name.

Every buffer has a mode associated with it which determines how keystrokes will be interpreted. It's recommended that each mode should be its own module. In that case you can create a mode like so:

(fn complete []

{:name "clam-mode"
 :parent "edit"
 :map {"tab" complete}
 :ctrl {"n" (fn [] (editor.print "you pressed ctrl-n!"))}
 :props {:activate (fn [] (global clam true))
         :deactivate (fn [] (global clam false))}}

And then add it with this code:

(local editor (require :polywell))

(editor.add-mode (require :config.clam-mode))

The :map table contains functions to handle various key presses. The handlers for ctrl/alt combinations are kept in the :ctrl and :alt entries. Setting :parent in a mode means that if a key binding isn't defined in the key maps you've provided, it will delegate to another mode and look it up in those key maps. You probably want your :parent set to "edit" if you're making a textual mode.


Each mode has a table of properties that can contain functions or other values which override its behaviour. Buffers can also have properties set which take precedence over mode properties.

Currently these properties are used:

  • on-change: a function which is called every time a change is made.
  • read-only: a boolean indicating whether edits should be allowed; this can be sidestepped by the polywell.suppress-read-only function, which takes a function as an arg to run with read-only checks disabled.
  • wrap: every time a command is run, it is run inside the wrap function which handles bookkeeping for undo; providing your own wrap allows you to implement your own undo.
  • render-lines: a table of lines in LÖVE's print format (color, string, color, string, etc) which is used instead of the raw lines table during rendering if present; used by syntax highlighting.
  • activate: (mode property only) a function called when a mode activates.
  • deactivate: (mode property only) a function called when a mode deactivates.
  • draw: a function to render the buffer instead of the default textual rendering.
  • update: a function which is run on every tick with a dt parameter, assuming polywell.update is called from love.update.

You can get and set properties on the current buffer with polywell.get-prop and polywell.set-prop, while mode properties are defined by the :props key in the table returned by the mode module.

Reading Input

The polywell.read-line function allows you to prompt the user for a line of input. It takes a prompt and a callback function. The callback function takes the string value which was input as its first argument.

(fn go-to-line []
  (editor.read-line "Go to line: "
                    (fn [line]
                      (editor.go_to (tonumber line)))))

When you read input, you can also offer live feedback as you type, like when you invoke the buffer switcher with ctrl-alt-b. The read_line function takes as a third argument a properties table, and if you provide a "completer" function, it will be called with the input string whenever the input changes. It must return a table of possible completion matches. You can use the polywell.completion.for function to calculate completion candidates; it takes a table of possible candidates and an input string.

See editor.find-file in polywell/commands.fnl for an example of how this can be used.

Syntax Highlighting

Currently Polywell ships with syntax highlighting for both Fennel code and Lua code. You can add support for new languages, but new language syntax highlighting support is limited to defining a new set of keywords and to-EOL comment markers for the language; the colorization of strings and numbers cannot be changed, nor can new constructs be added. See config/fennel-mode.fnl for an example.

Useful Functions

Most text editing commands should be fairly self-explanatory; see config/edit-mode.fnl for a listing.

The polywell.print and polywell.write functions print to the *console* buffer unless it is run within a call to with-output-to, which accepts an alternate buffer to which to redirect output and a function to run with the redirection active. For messages that do not need to stick around, use polywell.echo which just shows at the bottom of the screen until the next command.

The polywell.point function returns the point and line number. The line number obviously tells you which line you're on, and the point tells you how far over the cursor is in that line. You can use polywell.get-line to get a specific line as a string.

Use polywell.activate-mode to change the mode for the current buffer. The polywell.change-buffer function will switch to an existing buffer if it exists and do nothing if not, while polywell.open will switch or create if it's not found. The polywell.with-current-buffer function takes a buffer name and and function to run with that buffer active; it switches back to the original buffer when that function returns.