core Parinfer implementation for JavaScript

Usage no npm install needed!

<script type="module">
  import chrisoakmanParinfer from 'https://cdn.skypack.dev/@chrisoakman/parinfer';


Parinfer.js (updated fork)

Pronounced "par-in-fur". "par" rhymes with car and star; "fur" rhymes with blur and stir

This is a fork of shaunlebron's Parinfer library which was archived on Jan 2019.

The original repo was split into two separate parts: the library itself and a website that explains Parinfer.

This fork will contain only the parinfer.js library (and supporting tests).

npm package

This fork is published on npm under the package name @chrisoakman/parinfer

## using npm
npm install @chrisoakman/parinfer

## using yarn
yarn add @chrisoakman/parinfer


Parinfer consists of a couple pure functions of your text, returning new text with corrected parens or indentation.

// 'parinfer' is a global object if not used as Node module.
var parinfer = require('parinfer');

// Run Indent Mode on the given text:
var result = parinfer.indentMode("(def foo [a b");
// prints:
// (def foo [a b])

// Run Paren Mode on the given text:
var result = parinfer.parenMode("(def foo\n[a b\nc])");
// prints:
// (def foo
//  [a b
//   c])

Integrating with an Editor or REPL

See integrating.md


smartMode(text[, options])
indentMode(text[, options])
parenMode(text[, options])

Runs Indent Mode or Paren Mode on the given text. Smart Mode is currently something in between.


  • text is the full text input.
  • options is an object with the following properties:
    • commentChars - a character (ie: string of length 1) or array of characters that should be considered comments in the code (defaults to [";"])
    • cursorLine - zero-based line number of the cursor
    • cursorX - zero-based x-position of the cursor
    • prevCursorLine and prevCursorX is required by Smart Mode (previous cursor position)
    • selectionStartLine - first line of the current selection
    • changes - ordered array of change objects with the following:
      • lineNo - starting line number of the change
      • x - starting x of the change
      • oldText - original text that was replaced
      • newText - new text that replaced the original text
    • forceBalance - employ the aggressive paren-balancing rules from v1 (defaults to false)
    • partialResult - return partially processed text/cursor if an error occurs (defaults to false)

Returns an object with the following properties:

  • success is a boolean indicating if the input was properly formatted enough to create a valid result
  • text is the full text output (if success is false, returns original text unless partialResult is enabled)
  • cursorX/cursorLine is the new position of the cursor (since parinfer may shift it around)
  • error is an object populated if success is false:
    • name is the name of the error, which will be any of the following:
      • "quote-danger"
      • "eol-backslash"
      • "unclosed-quote"
      • "unclosed-paren"
      • "unmatched-close-paren"
      • "unhandled"
    • message is a message describing the error
    • lineNo is a zero-based line number where the error occurred
    • x is a zero-based column where the error occurred
    • extra has lineNo and x of open-paren for unmatched-close-paren
  • tabStops is an array of objects representing Tab stops, which is populated if a cursor position or selection is supplied. We identify tab stops at relevant open-parens, and supply the following extra information so you may compute extra tab stops for one-space or two-space indentation conventions based on the type of open-paren.
    • x is a zero-based x-position of the tab stop
    • argX position of the first argument after x (e.g. position of bar in (foo bar)
    • lineNo is a zero-based line number of the open-paren responsible for the tab stop
    • ch is the character of the open-paren responsible for the tab stop (e.g. (,[,{)
  • parenTrails is an array of object representing the Paren Trails at the end of each line that Parinfer may move
    • lineNo is a zero-based line number
    • startX is a zero-based x-position of the first close-paren
    • endX is a zero-based x-position after the last close-paren

Test API

You can use our testing API for a fast, visual way to specify options and verify results. This allows all metadata required by and returned from Parinfer to be specified inside the text using our annotation syntax.

See here for Annotation Syntax details

// Currently only supported in Node
var parinferTest = require('parinfer/test');

Test Example

The following code is a quick way to verify behavior of Indent Mode. The | is parsed as the cursor and removed from the text before processing.

(def foo
  "(a b)

This returns the processed text below, with | reinserted to show cursor result, and an ^ error annotation line since a string was not closed:

(def foo
  "(a b)
       ^ error: unclosed-quote

Test Usage

parinferTest.smartMode(inputText, extras); // returns string
parinferTest.indentMode(inputText, extras); // returns string
parinferTest.parenMode(inputText, extras);  // returns string

extras allows us to specify options for which there is no annotation syntax yet:

  • forceBalance
  • partialResult
  • printTabStops

You can also use the input/output functions directly:

parinferTest.parseInput(inputText, extras); // returns {text, options}
parinferTest.parseOutput(inputText, extras); // returns result

parinferTest.printOutput(result, extras);   // returns string

// `result` is returned by main indentMode or parenMode functions


Code: parinfer.js is implemented in ECMAScript 5 for easy speed and portability. Also:

Documentation: Code is documented in code.md.

Performance: To run a performance stress test:

node test/perf.js

Testing: See test/cases/ directory for testing details. Or just run the following:

npm install
npm test

Sandbox: See sandbox.js for how I manually test things (always changing based on what I'm currently working on).

A stable core for editor plugins

Want to use Parinfer on a team? Introduce Parlinter as your project's linter!

The behavior and implementation of the Parinfer library is stable and canonicalized. To allow different editors to use it, we have ported the implementation to the languages required by the plugin APIs of most major text editors. All language ports pass the same comprehensive test suite to help ensure consistent behavior.

implemented in link relevant editor
JavaScript parinfer.js (here) Atom, VSCode, LightTable
Rust parinfer-rust Vim
Python parinfer.py Sublime Text
Kotlin (JVM) parinfer-jvm Cursive IDE, Nightcode
Emacs Lisp parinfer-elisp Emacs
Vim Script parinfer-viml Vim

Open an issue if you would like Parinfer ported to another language for use in an editor not listed above.

Status Update 2019 (Smart Mode)

Smart Mode (available in [demo]) was an experiment to eliminate switching between Indent Mode and Paren Mode—by looking at a change and determining whether to run Indent Mode or Paren Mode. It is well tested and worked great in our sandboxes, but we found that the majority of editor APIs do not allow us to integrate Smart Mode's rules safely.

For example, if we don't catch a search/replace change in multiple locations of your document, but we infer from the next typing operation that we should run Indent Mode, then Smart Mode will make its decision without knowing the previous search/replace operation took place—thereby breaking its promise of choosing the best mode, and unsafely modifying your code.

The larger problem is that Smart Mode requires the synchronous interception of every type of change coming from the editor. It must decide the right thing to do for input changes at single/multiple cursors, search/replace, copy/paste, advanced macro operations, buffer refreshes from changes on disk, and maybe some others we haven't thought of yet. The interface for receiving these kinds of changes from the editor are not consistent—they either come in asynchronously or sychronously or not at all. This forces us to resort to computing diffs, a lossy mapping from changes to patches.

We have made separate attempts to implement Smart Mode in Cursive, Vim, Atom, and Emacs through some wrangling that made integration very difficult and delicate, and ultimately incomplete. Editors simply are not yet designed to allow an ideal version of Parinfer to exist—probably because nothing like Parinfer has demanded them before. The practicality of requesting these (likely non-trivial) changes on the editor is to be determined.


MIT License