javascript s-expression parser with quote support
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LICENSE Unquote-splicing support - version bump to 3.0.0 Mar 29, 2015 More info in README - no pairs Nov 10, 2015
index.js Fix error message for ,@ - was showing only , Nov 10, 2015

S-expression parser

[Recursive descent parser] 1 for [S-expressions] 2. It takes a string and returns the value that corresponds to one complete expression, or an Error.

Atoms are parsed to strings. String literals delimited by " are parsed into String objects to make them distinct from the other atoms. Escape sequences \", \\, \n, \r, \t, \f, and \b are supported. Lists are parsed to Arrays. Note this means that the result is not a binary tree. This also means there are no pairs or cons cells, and the expression (a . b) is parsed to ['a', '.', 'b'].

Supports quote, quasiquote, unquote, and unquote-splicing, with ', `, ,, and ,@ respectively.


var parse = require('s-expression');

console.log(parse('a')); // 'a'
console.log(parse('(a b "c")')); // ['a', 'b', [String: 'c']]
console.log(parse("'(a `(b ,c))")); // ['quote', ['a', ['quasiquote', ['b', ['unquote', 'c']]]]]


The returned Errors have two additional properties: line and col, which give you the line number and character column of the parse error in your input. Line means either LF or CRLF and column means one "character" as understood by javascript, so if you try to parse emoji, it will count them as two characters.

There are four kinds of errors:

  1. An unterminated string literal.
  2. Not an atom or string after a quote (', `, ,, ,@).
  3. The input ends before the expression is complete.
  4. There is more input after the expression is complete.


Contributions are welcome but please note that this project is meant to be a one-file parser without dependencies that is not too hard to understand.


This software is licensed under MIT, see LICENSE.