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Released: December 24, 2013
### Big Changes
* Completely rewrote the code generator. Among other things, it allows
optimizing generated parsers for parsing speed or code size using the
`optimize` option of the `PEG.buildParser` method or the `--optimize`/`-o`
option on the command-line. All internal identifiers in generated code now
also have a `peg$` prefix to discourage their use and avoid conflicts.
* Completely redesigned error handling. Instead of returning `null` inside
actions to indicate match failure, new `expected` and `error` functions can
be called to trigger an error. Also, expectation inside the `SyntaxError`
exceptions are now structured to allow easier machine processing.
* Implemented a plugin API. The list of plugins to use can be specified using
the `plugins` option of the `PEG.buildParser` method or the `--plugin`
option on the command-line. Also implemented the `--extra-options` and
`--extra-options-file` command-line options, which are mainly useful to pass
additional options to plugins.
* Made `offset`, `line` and `column` functions, not variables. They are now
available in all parsers and return lazily-computed position data. Removed
now useless `trackLineAndColumn` option of the `PEG.buildParser` method and
the `--track-line-and-column` option on the command-line.
* Added a new `text` function. When called inside an action, it returns the
text matched by action's expression.
* Added a new `$` operator. It extracts matched strings from expressions.
* The `?` operator now returns `null` on unsuccessful match.
* Predicates now always return `undefined`.
* Replaced the `startRule` parameter of the `parse` method in generated
parsers with more generic `options` parameter. The start rule can now be
specified as the `startRule` option. The `options` parameter can be also
used to pass custom options to the parser because it is visible as the
`options` variable inside parser code.
* The list of allowed start rules of a generated parser now has to be
specified explicitly using the `allowedStartRules` option of the
`PEG.buildParser` method or the `--allowed-start-rule` option on the
command-line. This will make certain optimizations like rule inlining easier
in the future.
* Removed the `toSource` method of generated parsers and introduced a new
`output` option of the `PEG.buildParser` method. It allows callers to
specify whether they want to get back the parser object or its source code.
* The source code is now a valid npm package. This makes using development
versions easier.
* Generated parsers are now ~25% faster and ~62%/~3% smaller (when optimized
for size/speed) than those generated by 0.7.0.
* Requires Node.js 0.8.0+.
### Small Changes
* `bin/pegjs` now outputs just the parser source if the value of the
`--export-var` option is empty. This makes embedding generated parsers into
other files easier.
* Changed the value of the `name` property of `PEG.GrammarError` instances
from “PEG.GrammarError” to just “GrammarError”. This better reflects the
fact that PEG.js can get required with different variable name than `PEG`.
* Setup prototype chain for `PEG.GrammarError` correctly.
* Setup prototype chain for `SyntaxError` in generated parsers correctly.
* Fixed error messages in certain cases with trailing input
* Fixed code generated for classes starting with `\^`.
* Fixed too eager proxy rules removal.
* Added a license to all vendored libraries.
* Converted the test suite from QUnit to Jasmine, cleaning it up on the way.
* Travis CI integration.
* Various internal code improvements and fixes.
* Various generated code improvements and fixes.
* Various example grammar improvements and fixes.
* Improved ``.
* Converted `CHANGELOG` to Markdown.
Released: April 18, 2012
### Big Changes
* Added ability to pass options to `PEG.buildParser`.
* Implemented the `trackLineAndColumn` option for `PEG.buildParser` (together
with the `--track-line-and-column` command-line option). It makes the
generated parser track line and column during parsing. These are made
available inside actions and predicates as `line` and `column` variables.
* Implemented the `cache` option for `PEG.buildParser` (together with the
`--cache` command-line option). This option enables/disables the results
cache in generated parsers, resulting in dramatic speedup when the cache is
disabled (the default now). The cost is breaking the linear parsing time
* The current parse position is visible inside actions and predicates as the
`offset` variable.
* Exceptions thrown by the parser have `offset`, `expected` and `found`
properties containing machine-readable information about the parse failure
(based on a patch by Marcin Stefaniuk).
* Semantic predicates have access to preceding labels.
* Implemented case-insensitive literal and class matching.
* Rewrote the code generator — split some computations into separate passes
and based it on a proper templating system (Codie).
* Rewrote variable handling in generated parsers in a stack-like fashion,
simplifying the code and making the parsers smaller and faster.
* Adapted to Node.js 0.6.6+ (no longer supported in older versions).
* Dropped support for IE < 8.
* As a result of several optimizations, parsers generated by 0.7.0 are ~6.4
times faster and ~19% smaller than those generated by 0.6.2 (as reported by
### Small Changes
* Fixed reported error position when part of the input is not consumed.
* Fixed incorrect disjunction operator in `computeErrorPosition` (original
patch by Wolfgang Kluge).
* Fixed regexp for detecting command-line options in `/bin/pegjs`.
* Generate more efficient code for empty literals (original patch by Wolfgang
* Fixed comment typos (patches by Wolfgang Kluge and Jason Davies).
* Fixed a typo in JavaScript example grammar.
* Made copy & paste inclusion of the PEG.js library into another code easier
by changing how the library is exported.
* Improved the copyright comment and the “Generated by...” header.
* Replaced `Jakefile` with `Makefile`.
* Added `make hint` task that checks all JavaScript files using JSHint and
resolved all issues it reported. All JavaScript files and also generated
parsers are JSHint-clean now.
* Fixed output printed during test failures (expected value was being printed
instead of the actual one). Original patch by Wolfgang Kluge.
* Added a `/tools/impact` script to measure speed and size impact of commits.
* Various generated code improvements and fixes.
* Various internal code improvements and fixes.
* Improved ``.
Released: August 20, 2011
### Small Changes
* Reset parser position when action returns `null`.
* Fixed typo in JavaScript example grammar.
Released: April 14, 2011
### Small Changes
* Use `--ascii` option when generating a minified version.
Released: April 14, 2011
### Big Changes
* Rewrote the command-line mode to be based on Node.js instead of Rhino — no
more Java dependency. This also means that PEG.js is available as a Node.js
package and can be required as a module.
* Version for the browser is built separately from the command-line one in two
flavors (normal and minified).
* Parser variable name is no longer required argument of `bin/pegjs` — it is
`module.exports` by default and can be set using the `-e`/`--export-var`
option. This makes parsers generated by `/bin/pegjs` Node.js modules by
* Added ability to start parsing from any grammar rule.
* Added several compiler optimizations — 0.6 is ~12% faster than 0.5.1 in the
benchmark on V8.
### Small Changes
* Split the source code into multiple files combined together using a build
* Jake is now used instead of Rake for build scripts — no more Ruby
* Test suite can be run from the command-line.
* Benchmark suite can be run from the command-line.
* Benchmark browser runner improvements (users can specify number of runs,
benchmarks are run using `setTimeout`, table is centered and fixed-width).
* Added PEG.js version to “Generated by...” line in generated parsers.
* Added PEG.js version information and homepage header to `peg.js`.
* Generated code improvements and fixes.
* Internal code improvements and fixes.
* Rewrote ``.
Released: November 28, 2010
### Small Changes
* Fixed a problem where “SyntaxError: Invalid range in character class.” error
appeared when using command-line version on Widnows
* Fixed wrong version reported by `bin/pegjs --version`.
* Removed two unused variables in the code.
* Fixed incorrect variable name on two places.
Released: June 10, 2010
### Big Changes
* Syntax change: Use labeled expressions and variables instead of `$1`, `$2`,
* Syntax change: Replaced `:` after a rule name with `=`.
* Syntax change: Allow trailing semicolon (`;`) for rules
* Semantic change: Start rule of the grammar is now implicitly its first rule.
* Implemented semantic predicates.
* Implemented initializers.
* Removed ability to change the start rule when generating the parser.
* Added several compiler optimizations — 0.5 is ~11% faster than 0.4 in the
benchmark on V8.
### Small Changes
* `PEG.buildParser` now accepts grammars only in string format.
* Added “Generated by ...” message to the generated parsers.
* Formatted all grammars more consistently and transparently.
* Added notes about ECMA-262, 5th ed. compatibility to the JSON example
* Guarded against redefinition of `undefined`.
* Made `bin/pegjs` work when called via a symlink
([issue #1](
* Fixed bug causing incorrect error messages
([issue #2](
* Fixed error message for invalid character range.
* Fixed string literal parsing in the JavaScript grammar.
* Generated code improvements and fixes.
* Internal code improvements and fixes.
* Improved ``.
Released: April 17, 2010
### Big Changes
* Improved IE compatibility — IE6+ is now fully supported.
* Generated parsers are now standalone (no runtime is required).
* Added example grammars for JavaScript, CSS and JSON.
* Added a benchmark suite.
* Implemented negative character classes (e.g. `[^a-z]`).
* Project moved from BitBucket to GitHub.
### Small Changes
* Code generated for the character classes is now regexp-based (= simpler and
more scalable).
* Added `\uFEFF` (BOM) to the definition of whitespace in the metagrammar.
* When building a parser, left-recursive rules (both direct and indirect) are
reported as errors.
* When building a parser, missing rules are reported as errors.
* Expected items in the error messages do not contain duplicates and they are
* Fixed several bugs in the example arithmetics grammar.
* Converted `README` to GitHub Flavored Markdown and improved it.
* Added `CHANGELOG`.
* Internal code improvements.
Released: March 14, 2010
* Wrote `README`.
* Bootstrapped the grammar parser.
* Metagrammar recognizes JavaScript-like comments.
* Changed standard grammar extension from `.peg` to `.pegjs` (it is more
* Simplified the example arithmetics grammar + added comment.
* Fixed a bug with reporting of invalid ranges such as `[b-a]` in the
* Fixed `--start` vs. `--start-rule` inconsistency between help and actual
option processing code.
* Avoided ugliness in QUnit output.
* Fixed typo in help: `parserVar``parser_var`.
* Internal code improvements.
Released: March 8, 2010
* Added `pegjs-` prefix to the name of the minified runtime file.
Released: March 8, 2010
* Added `Rakefile` that builds minified runtime using Google Closure Compiler
* Removed trailing commas in object initializers (Google Closure does not like
Released: March 8, 2010
* Initial release.