This is purely a mechanical change, not taking advantage of block scope
of "let" and "const". Minimizing variable scope will come in the next
commit.
In general, "var" is converted into "let" and "const" is used only for
immutable variables of permanent character (generally spelled in
ALL_CAPS). Using it for any immutable variable regardless on its
permanence would feel confusing.
Any code which is not transpiled and needs to run in ES6 environment
(examples, code in grammars embedded in specs, ...) is kept unchanged.
This is also true for code generated by PEG.js.
See #442.
Parsers generated in this format use module.exports, so they are not
strictly CommonJS, but this is a common extension and the original name
would be confusing once Node.js implements ES2015 modules.
This is more traditional compiler interface. Its main advantage against
specifying the output file as a second argument (which is what bin/pegjs
used until now) is that input and output files can't be mixed up.
Part of #370.
This will make room for -o to mean --output instead of --optimize. Also,
-O is more traditional option name for describing optimization config
than -o.
Part of #370.
In most places, we talk about "generating a parser", not "building a
parser", which the function name should reflect. Also, mentioning a
parser in the name is not necessary as in case of a parser generator
it's pretty clear what is generated.
So far, PEG.js was exported in a "PEG" global variable when no module
loader was detected. The same variable name was also conventionally used
when requiring it in Node.js or otherwise referring to it. This was
reflected in various places in the code, documentation, examples, etc.
This commit changes the variable name to "peg" and fixes all relevant
occurrences. The main reason for the change is that in Node.js, modules
are generally referred to by lower-case variable names, so "PEG" was
sticking out when used in Node.js projects.
Introduce two ways of specifying parser dependencies: the "dependencies"
option of PEG.buildParser and the -d/--dependency CLI option. Specified
dependencies are translated into AMD dependencies and Node.js's
"require" calls when generating an UMD parser.
Part of work on #362.
Running bin/pegjs with one argument which was an extension-less file
name caused the file to be overwritten. This was because internal
extension rewriting logic didn't handle this case corectly.
This commit changes the logic from regexp-based to path.extname-based,
fixing the problem. The new code generates file names like this:
Input file name Output file name
------------------------------------
grammar.ext grammar.js
grammar.ext1.ext2 grammar.ext1.js
grammar. grammar.js
grammar grammar.js
Fixes#405.
Instead of setting ESLint environment to "node" globally, set it on
per-directory basis using separate .eslintrc.json files:
Directory Environment
-----------------------
bin node
lib commonjs
spec jasmine
It was impossible to use this approach for the "benchmark" directory
which contains a mix of files used in various environments. For
benchmark/run, the environment is set inline. For the other files, as
well as spec/helpers.js, the globals are declared manually (it is
impossible to express how these files are used just by a list of
environments).
Fixes#408.
The |util.puts| and |util.error| functions are deprecated in Node.js
0.12.x.
Based on a pull request by Jan Stránský (@burningtree):
https://github.com/pegjs/pegjs/pull/334
Replace |line|, |column|, and |offset| properties of |SyntaxError| with
the |location| property. It contains an object similar to the one
returned by the |location| function available in action code:
{
start: { offset: 23, line: 5, column: 6 },
end: { offset: 25, line: 5, column: 8 }
}
For syntax errors produced in the middle of the input, |start| refers to
the first unparsed character and |end| refers to the character behind it
(meaning the span is 1 character). This corresponds to the portion of
the input in the |found| property.
For syntax errors produced the end of the input, both |start| and |end|
refer to a character past the end of the input (meaning the span is 0
characters).
For syntax errors produced by calling |expected| or |error| functions in
action code the location info is the same as the |location| function
would return.
Parsers can now be generated with support for tracing using the --trace
CLI option or a boolean |trace| option to |PEG.buildParser|. This makes
them trace their progress, which can be useful for debugging. Parsers
generated with tracing support are called "tracing parsers".
When a tracing parser executes, by default it traces the rules it enters
and exits by writing messages to the console. For example, a parser
built from this grammar:
start = a / b
a = "a"
b = "b"
will write this to the console when parsing input "b":
1:1 rule.enter start
1:1 rule.enter a
1:1 rule.fail a
1:1 rule.enter b
1:2 rule.match b
1:2 rule.match start
You can customize tracing by passing a custom *tracer* to parser's
|parse| method using the |tracer| option:
parser.parse(input, { trace: tracer });
This will replace the built-in default tracer (which writes to the
console) by the tracer you supplied.
The tracer must be an object with a |trace| method. This method is
called each time a tracing event happens. It takes one argument which is
an object describing the tracing event.
Currently, three events are supported:
* rule.enter -- triggered when a rule is entered
* rule.match -- triggered when a rule matches successfully
* rule.fail -- triggered when a rule fails to match
These events are triggered in nested pairs -- for each rule.enter event
there is a matching rule.match or rule.fail event.
The event object passed as an argument to |trace| contains these
properties:
* type -- event type
* rule -- name of the rule the event is related to
* offset -- parse position at the time of the event
* line -- line at the time of the event
* column -- column at the time of the event
* result -- rule's match result (only for rule.match event)
The whole tracing API is somewhat experimental (which is why it isn't
documented properly yet) and I expect it will evolve over time as
experience is gained.
The default tracer is also somewhat bare-bones. I hope that PEG.js user
community will develop more sophisticated tracers over time and I'll be
able to integrate their best ideas into the default tracer.
Also added few missing |hasOwnProperty| calls that JSHint didn't detect
because it only looks whether there is an |if| statement wrapping the
loop body.
Fixes the following JSHint errors:
bin/pegjs: line 66, col 14, 'extraOptions' used out of scope.
bin/pegjs: line 70, col 19, 'extraOptions' used out of scope.
bin/pegjs: line 71, col 20, 'extraOptions' used out of scope.
bin/pegjs: line 80, col 10, Wrap the /regexp/ literal in parens to disambiguate the slash operator.
bin/pegjs: line 128, col 43, Missing semicolon.
bin/pegjs: line 128, col 45, Don't make functions within a loop.
bin/pegjs: line 150, col 13, Redefinition of 'module'.
bin/pegjs: line 217, col 34, Expected '===' and instead saw '=='.
bin/pegjs: line 243, col 44, 'source' used out of scope.
bin/pegjs: line 243, col 61, 'source' used out of scope.
This is a complete rewrite of the PEG.js code generator. Its goals are:
1. Allow optimizing the generated parser code for code size as well as
for parsing speed.
2. Prepare ground for future optimizations and big features (like
incremental parsing).
2. Replace the old template-based code-generation system with
something more lightweight and flexible.
4. General code cleanup (structure, style, variable names, ...).
New Architecture
----------------
The new code generator consists of two steps:
* Bytecode generator -- produces bytecode for an abstract virtual
machine
* JavaScript generator -- produces JavaScript code based on the
bytecode
The abstract virtual machine is stack-based. Originally I wanted to make
it register-based, but it turned out that all the code related to it
would be more complex and the bytecode itself would be longer (because
of explicit register specifications in instructions). The only downsides
of the stack-based approach seem to be few small inefficiencies (see
e.g. the |NIP| instruction), which seem to be insignificant.
The new generator allows optimizing for parsing speed or code size (you
can choose using the |optimize| option of the |PEG.buildParser| method
or the --optimize/-o option on the command-line).
When optimizing for size, the JavaScript generator emits the bytecode
together with its constant table and a generic bytecode interpreter.
Because the interpreter is small and the bytecode and constant table
grow only slowly with size of the grammar, the resulting parser is also
small.
When optimizing for speed, the JavaScript generator just compiles the
bytecode into JavaScript. The generated code is relatively efficient, so
the resulting parser is fast.
Internal Identifiers
--------------------
As a small bonus, all internal identifiers visible to user code in the
initializer, actions and predicates are prefixed by |peg$|. This lowers
the chance that identifiers in user code will conflict with the ones
from PEG.js. It also makes using any internals in user code ugly, which
is a good thing. This solves GH-92.
Performance
-----------
The new code generator improved parsing speed and parser code size
significantly. The generated parsers are now:
* 39% faster when optimizing for speed
* 69% smaller when optimizing for size (without minification)
* 31% smaller when optimizing for size (with minification)
(Parsing speed was measured using the |benchmark/run| script. Code size
was measured by generating parsers for examples in the |examples|
directory and adding up the file sizes. Minification was done by |uglify
--ascii| in version 1.3.4.)
Final Note
----------
This is just a beginning! The new code generator lays a foundation upon
which many optimizations and improvements can (and will) be made.
Stay tuned :-)
Getting rid of the |trackLineAndColumn| simplifies the code generator
(by unifying two paths in the code).
The |line| and |column| functions currently always compute all the
position info from scratch, which is horribly ineffective. This will be
improved in later commit(s).
Before this commit, |PEG.buildParser| always returned a parser object.
The only way to get its source code was to call the |toSource| method on
it. While this method worked for parsers produced by |PEG.buildParser|
directly, it didn't work for parsers instantiated by executing their
source code. In other words, it was unreliable.
This commit remvoes the |toSource| method on generated parsers and
introduces a new |output| option to |PEG.buildParser|. It allows callers
to specify whether they want to get back the parser object
(|options.output === "parser"|) or its source code (|options.output ===
"source"|). This is much better and more reliable API.
Before this commit, generated parser were able to start parsing from any
rule. This was nice, but it made rule code inlining impossible.
Since this commit, the list of allowed start rules has to be specified
explicitly using the |allowedStartRules| option of the |PEG.buildParser|
method (or the --allowed-start-rule option on the command-line). These
rules will be excluded from inlining when it's implemented.
While |process.openStdin| is not officially deprecated, it's no longer
documented and just using |process.stdin| and resuming it seems to be
the official way.
The previous default name was "exports.parser". This meant that to use
the generated parser in Node.js, you had to use code like this:
var parser = require("./my-cool-parser").parser;
parser.parse(...);
Now you can shorten it a bit:
var parser = require("./my-cool-parser");
parser.parse(...);
The shorter version makes sense since no other objects except the parser
are exported from the module.
The source code is now in the src directory. The library needs to be
built using "rake", which creates the lib/peg.js file by combining the
source files.
David Majda
Arlo Breault