This is mostly done for consistency with the JavaScript example grammar,
from which the |Identifier| rule is taken from. See the previous commit
for details.
Instead of matching segments between blocks character by character,
match them as a whole. Also align the style with other similar rules
(e.g. the comment ones).
Before this commit, line continuations in character classes contributed
an empty string to the list of characters and character ranges matched
by a class. While this didn't lead to a buggy behavior with the current
code generator, the AST was wrong and the problem could have caused bugs
later.
This commit fixes the problem.
Semantic predicates are kind of |PrimaryExpression|, not kind of
|PrefixedExpression|. Therefore I extracted a rule for them and
referenced it from the |PrimaryExpression|.
Initializer and rules are now separated in a similar way as JavaScript
statements -- either by a semicolon or a line terminator, possibly with
whitespace and comments mixed in.
One consequence is that the grammars like this are now illegal:
foo = "a" bar = "b"
A semicolon needs to be inserted between the rules:
foo = "a";bar = "b"
I consider this a good change as the now-illegal syntax was somewhat
confusing.
This makes the |Primary| rule a bit more tidy. Also, matching the |.|
character really belongs to the lexical part of the grammar, next to
literals and character classes.
* Rename the |Action| rule to |CodeBlock| (it better describes what
the rule matches).
* Implement the rule in a simpler way and move it after more basic
lexical elements.
This change has two side effects:
* Label names can no longer be JavaScript reserved words.
* |$| is allowed again in label names. However, because of the
preference rules, names starting with it will be usually parsed as a
text operator followed by another identifier (denoting a rule
reference or label name).
Before this commit, whitespace was handled at the lexical level by
making tokens consume any whitespace coming after them. This was
accomplished by appending |__| to every token rule.
This commit changes whitespace handling to be more explicit. Tokens no
longer consume whitespace coming after them and syntactic rules have to
cope with it. While this slightly complicates the syntactic grammar, I
think it's a cleaner way. Moreover, it is what JavaScript example
grammar does.
One small side-effect of thich change is that the grammar is now
stand-alone (it doesn't require utils.js anymore).
When rule names are capitalized, it's easier to visually distinguish
them from non-capitalized label names. Moreover, I use capitalized rule
names in all my grammars these days.
Before this commit, a line continuation (backslash followed by a line
terminator character) contributed a character to a string or a character
class it was used in. In JavaScript and many other languages, line
continuation doesn't contribute anything.
This commit aligns PEG.js line continuation behavior with JavaScript.
Before this commit, the value of the |rawText| property of "class" AST
nodes was created in a hackish way from processed input and it didn't
always exactly represent the actual input text.
This commit changes the code so that the value of the |rawText| property
is created using the |text| function. This is a clean way which also
resolves the exact representation problem.
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 error:
lib/compiler/passes/generate-bytecode.js: line 334, col 71, Expected an assignment or function call and instead saw an expression.
The one-parameter |Array.prototype.splice| call is a SpiderMonkey
extension. Apparently, IE doesn't implement it (unlike other supported
browsers), so we need to replace it with two-parameter version.
In case the generated parser parsed successfully part of input and left
some input unparsed (trailing input), the error message produced was
sometimes wrong. The code worked correctly only if there were no match
failures in the successfully parsed part (highly unlikely).
This commit fixes things by explicitly triggering a match failure with the
following expectation at the end of the successfully parsed part of the
input:
peg$fail({ type: "end", description: "end of input" });
This change also made it possible to simplify the |buildMessage|
function, which can now ignore the case of no expectations.
Fixes#119.
There are two invariants in generated bytecode related to the stack:
1. Branches of a condition must move the stack pointer in the same way.
2. Body of a loop can't move the stack pointer.
These invariants were always true, but they were not checked. Now we
check them at least when compiling with optimization for speed, because
there we analyze the stack pointer movements statically.
The error check was useful when actions could have returned |null| to
trigger a match failure. This is no longer supported so the check isn't
needed anymore.
Speed impact
------------
Before: 1022.70 kB/s
After: 1035.45 kB/s
Difference: 1.24%
Size impact
-----------
Before: 975434 b
After: 931540 b
Difference: -4.50%
(Measured by /tools/impact with Node.js v0.6.18 on x86_64 GNU/Linux.)
Before this commit, the |expected| and |error| functions didn't halt the
parsing immediately, but triggered a regular match failure. After they
were called, the parser could backtrack, try another branches, and only
if no other branch succeeded, it triggered an exception with information
possibly based on parameters passed to the |expected| or |error|
function (this depended on positions where failures in other branches
have occurred).
While nice in theory, this solution didn't work well in practice. There
were at least two problems:
1. Action expression could have easily triggered a match failure later
in the input than the action itself. This resulted in the
action-triggered failure to be shadowed by the expression-triggered
one.
Consider the following example:
integer = digits:[0-9]+ {
var result = parseInt(digits.join(""), 10);
if (result % 2 === 0) {
error("The number must be an odd integer.");
return;
}
return result;
}
Given input "2", the |[0-9]+| expression would record a match
failure at position 1 (an unsuccessful attempt to parse yet another
digit after "2"). However, a failure triggered by the |error| call
would occur at position 0.
This problem could have been solved by silencing match failures in
action expressions, but that would lead to severe performance
problems (yes, I tried and measured). Other possible solutions are
hacks which I didn't want to introduce into PEG.js.
2. Triggering a match failure in action code could have lead to
unexpected backtracking.
Consider the following example:
class = "[" (charRange / char)* "]"
charRange = begin:char "-" end:char {
if (begin.data.charCodeAt(0) > end.data.charCodeAt(0)) {
error("Invalid character range: " + begin + "-" + end + ".");
}
// ...
}
char = [a-zA-Z0-9_\-]
Given input "[b-a]", the |charRange| rule would fail, but the
parser would try the |char| rule and succeed repeatedly, resulting
in "b-a" being parsed as a sequence of three |char|'s, which it is
not.
This problem could have been solved by using negative predicates,
but that would complicate the grammar and still wouldn't get rid of
unintuitive behavior.
Given these problems I decided to change the semantics of the |expected|
and |error| functions. They don't interact with regular match failure
mechanism anymore, but they cause and immediate parse failure by
throwing an exception. I think this is more intuitive behavior with less
harmful side effects.
The disadvantage of the new approach is that one can't backtrack from an
action-triggered error. I don't see this as a big deal as I think this
will be rarely needed and one can always use a semantic predicate as a
workaround.
Speed impact
------------
Before: 993.84 kB/s
After: 998.05 kB/s
Difference: 0.42%
Size impact
-----------
Before: 1019968 b
After: 975434 b
Difference: -4.37%
(Measured by /tools/impact with Node.js v0.6.18 on x86_64 GNU/Linux.)
The |error| function allows users to report custom match failures inside
actions.
If the |error| function is called, and the reported match failure turns
out to be the cause of a parse error, the error message reported by the
parser will be exactly the one specified in the |error| call.
Implements part of #198.
Speed impact
------------
Before: 999.83 kB/s
After: 1000.84 kB/s
Difference: 0.10%
Size impact
-----------
Before: 1017212 b
After: 1019968 b
Difference: 0.27%
(Measured by /tools/impact with Node.js v0.6.18 on x86_64 GNU/Linux.)
This is in anticipation of |peg$error|. The |peg$expected| and
|peg$error| internal functions will nicely mirror the |expected| and
|error| functions available to user code in actions.
Implements part of #198.
The |expected| function allows users to report regular match failures
inside actions.
If the |expected| function is called, and the reported match failure
turns out to be the cause of a parse error, the error message reported
by the parser will be in the usual "Expected ... but found ..." format
with the description specified in the |expected| call used as part of
the message.
Implements part of #198.
Speed impact
------------
Before: 1146.82 kB/s
After: 1031.25 kB/s
Difference: -10.08%
Size impact
-----------
Before: 950817 b
After: 973269 b
Difference: 2.36%
(Measured by /tools/impact with Node.js v0.6.18 on x86_64 GNU/Linux.)
After making the |?| operator return |null| instead of an empty string
in the previous commit, empty strings were still returned from
predicates. This didn't make much sense.
Return value of a predicate is unimportant (if you have one in hand, you
already know the predicate succeeded) and one could even argue that
predicates shouldn't return any value at all. The closest thing to
"return no value" in JavaScript is returning |undefined|, so I decided
to make predicates return exactly that.
Implements part of #198.
Before this commit, the |?| operator returned an empty string upon
unsuccessful match. This commit changes the returned value to |null|. It
also updates the PEG.js grammar and the example grammars, which used the
value returned by |?| quite often.
Returning |null| is possible because it no longer indicates a match
failure.
I expect that this change will simplify many real-world grammars, as an
empty string is almost never desirable as a return value (except some
lexer-level rules) and it is often translated into |null| or some other
value in action code.
Implements part of #198.
Using a special value to indicate match failure instead of |null| allows
actions to return |null| as a regular value. This simplifies e.g. the
JSON parser.
Note the special value is internal and intentionally undocumented. This
means that there is currently no official way how to trigger a match
failure from an action. This is a temporary state which will be fixed
soon.
The negative performance impact (see below) is probably caused by
changing lot of comparisons against |null| (which likely check the value
against a fixed constant representing |null| in the interpreter) to
comparisons against the special value (which likely check the value
against another value in the interpreter).
Implements part of #198.
Speed impact
------------
Before: 1146.82 kB/s
After: 1031.25 kB/s
Difference: -10.08%
Size impact
-----------
Before: 950817 b
After: 973269 b
Difference: 2.36%
(Measured by /tools/impact with Node.js v0.6.18 on x86_64 GNU/Linux.)
Before this commit, the |expected| property of an exception object
thrown when a generated parser encountered an error contained
expectations as strings. These strings were in a human-readable format
suitable for displaying in the UI but not suitable for machine
processing. For example, expected string literals included quotes and a
string "any character" was used when any character was expected.
This commit makes expectations structured objects. This makes the
machine processing easier, while still allowing to generate a
human-readable representation if needed.
Implements part of #198.
Speed impact
------------
Before: 1180.41 kB/s
After: 1165.31 kB/s
Difference: -1.28%
Size impact
-----------
Before: 863523 b
After: 950817 b
Difference: 10.10%
(Measured by /tools/impact with Node.js v0.6.18 on x86_64 GNU/Linux.)
In the bytecode generator, the |context.action| property wasn't
correctly reset when generating bytecode for sequence elements. As a
result, when a sequence was wrapped in an action and it contained
another sequence as an element, the generator thought that the inner
sequence was wrapped in an action too.
For example, the following grammar:
start = ("a" "b") "c" { return "x"; }
was compiled as if it looked like this:
start = ("a" "b" { return "x"; }) "c" { return "x"; }
This commit fixes the problem by resetting |context.action| correctly.
Fixes GH-168.
Code that calculated which part of the input to match against a literal
was wrong in case of case-insensitive literals when generating
speed-optimized parsers. As a result, matching of case-insensitive
literals worked only at the end of the input (where too big length
passed to the |substr| method didn't matter).
Fixes GH-153.
The deduplication skipped over an expected string right after the one
that was removed because the index variable was incorrectly incremented
in that case.
Based on a patch by @fresheneesz:
https://github.com/dmajda/pegjs/pull/146
The compiler passes are now split into three stages:
* check -- passes that check for various error conditions
* transform -- passes that transform the AST (e.g. to perform
optimizations)
* generate -- passes that are related to code generation
Splitting the passes into stages is important for plugins. For example,
if a plugin wants to add a new optimization pass, it can add it at the
end of the "transform" stage without any knowledge about other passes it
contains. Similarly, if it wants to generate something else than the
default code generator does from the AST, it can just replace all passes
in the "generate" stage by its own one(s).
More generally, the stages make it possible to write plugins that do not
depend on names and actions of specific passes (which I consider
internal and subject of change), just on the definition of stages (which
I consider a public API with to which semver rules apply).
Implements part of GH-106.
The |plugins| option allows users to use plugins that change how PEG.js
operates.
A plugin is any JavaScript object with a |use| method. After the user
calls |PEG.buildParser|, this method is called for each plugin with the
following two parameters:
* PEG.js config that describes used grammar parser and compiler
passes used to generate the parser
* options passed by user to |PEG.buildParser|
The plugin is expected to change the config as needed, possibly based on
the options passed by user. It can e.g. change the used grammar parser,
change the compiler passes (including adding its own), etc. This way it
can extend PEG.js in a flexible way.
Implements part of GH-106.
The |passes| parameter will allow to pass the list of passes from
|PEG.buildParser|. This will be used by plugins. The old way via setting
the |appliedPassNames| property is removed.
Implements part of GH-106.
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 :-)
Previously, the report-left-recursion and report-missing-rules passes
used PEG.GrammarError without requiring it, causing a ReferenceError.
Since requiring lib/peg.js would cause circular requirements, this
commit imports lib/grammar-error.js as GrammarError.
The bug was introduced in commit
4cda79951a.
Fixes GH-135.
When called inside an action, the |text| function returns the text
matched by action's expression. It can be also called inside an
initializer or a predicate where it returns an empty string.
The |text| function will be useful mainly in cases where one needs a
structured representation of the input and simultaneously the raw text.
Until now, the only way to get the raw text in these cases was to
painfully build it from the structured representation.
Fixes GH-131.
Implement a new syntax to extract matched strings from expressions. For
example, instead of:
identifier = first:[a-zA-Z_] rest:[a-zA-Z0-9_]* { return first + rest.join(""); }
you can now just write:
identifier = $([a-zA-Z_] [a-zA-Z0-9_]*)
This is useful mostly for "lexical" rules at the bottom of many
grammars.
Note that structured match results are still built for the expressions
prefixed by "$", they are just ignored. I plan to optimize this later
(sometime after the code generator rewrite).
Cache the last reported position info. If the position advances, the
code uses the cache and only computes the differnece. If the position
goes back, the cache is simply dropped.
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).
This will allow to compute position data lazily and get rid of the
|trackLineAndColumn| option without affecting performance of generated
parsers that don't use position data.
Before this commit, incorrect regexps were produced for classes starting
with "\^". For example, this grammar:
start = [\^a]
didn't match "a" because the generated regexp inside the parser was
/^[^a]/, not /^[\^a]/ as it should be.
This commit fixes the issue by escaping "^" in |quoteForRegexpClass|.
Fixes GH-125.
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.
Includes:
* Moving the source code from /src to /lib.
* Adding an explicit file list to package.json
* Updating the Makefile.
* Updating the spec and benchmark suites and their READMEs.
Part of a fix for GH-32.
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.
1. |PEG.Compiler| -> |PEG.compiler|
2. |PEG.grammarParser| -> |PEG.parser|
This brings us closer to the desired structure of the PEG object, which
is:
+-PEG
|- parser
+- compiler
|- checks
|- passes
+- emitter
These are the only things (together with the |PEG.buildParser| function
and exceptions) that I want to be publicly accessible -- as extension
points and also for easy testing of PEG.js's components.
Before this change, the start rule was the one named "start" and there
was an option to override that. This is now impossible.
The goal of this change is to contain all information for the parser
generation in the grammar itself.
In the future, some override directive for the start rule (like Bison's
"%start") may be added to the grammar.
Little change in the source grammar now does not change variables in all
the generated code. This is helpful especially when one has the
generated grammar stored in a VCS (this is true e.g. for our
metagrammar).
We want to have the rule parsing functions inside the |parse| method
because we want them to share a common environment. In the future,
initializers will be executed in this enviromnent and thus functions and
variables defined by them will be accessible to the rule parsing
functions.
Moving various private properties from the parser object into the
|parse| method was not strictly necessary, but it was a natural step
after moving the functions.
Labeled expressions lead to more maintainable code and also will allow
certain optimizations (we can ignore results of expressions not passed
to the actions).
This does not speed up the benchmark suite execution statistically
significantly on V8.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 28.43 kB/s 28.46 kB/s
2 28.38 kB/s 28.56 kB/s
3 28.22 kB/s 28.58 kB/s
4 28.76 kB/s 28.55 kB/s
5 28.57 kB/s 28.48 kB/s
---------------------------------
Average 28.47 kB/s 28.53 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.4 (KHTML, like Gecko) Chrome/5.0.375.55 Safari/533.4
I'll introduce labelled expressions shortly and I want to use ":" as a
label-expression separator. This change avoids conflict between the two
meanings of ":". (What would e.g. "foo: 'bar'" mean? Rule "foo"
matching string "bar", or string "bar" labelled "foo"?)
This shouldn't have measurable effect on the benchmarks as there are no
proxy rules in the grammars the benchamrk uses. However the effect on
generated parsers' speed should be positive generally.
In most cases, code pattern
x === undefined
was transformed to
typeof(x) === "undefined"
and similarly with |!==|.
In the generated code, the condition was simply made less strict to
avoid performance penalty of string comparison (I don't think JavaScript
VMs optimize this specific pattern to avoid it).
This speeds up the benchmark suite execution by 0.18%, which may just be a
measurement error. (Standrad statistic tests would tell more, but I don't want
to mess with them now.) The code is little bit nicer this way though.
Going further and avoiding |apply| seems to slow thigs down a bit, possibly
because multiple array accesses. I may try improved version without array
accesses (where Action passes the Sequence variable names to save the results
into) sometime later.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 29.08 kB/s 28.91 kB/s
2 28.72 kB/s 28.75 kB/s
3 28.78 kB/s 28.88 kB/s
4 28.57 kB/s 28.90 kB/s
5 28.84 kB/s 28.81 kB/s
---------------------------------
Average 28.80 kB/s 28.85 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.2 (KHTML, like Gecko) Chrome/5.0.342.9 Safari/533.2
The action now computes the number of passed parameters during the code
generation and the parameters are declared directly as $1, $2, etc. in the
generated function.
This does not speed up the benchmark suite execution statistically significantly
on V8.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 28.68 kB/s 29.08 kB/s
2 28.77 kB/s 28.72 kB/s
3 28.89 kB/s 28.78 kB/s
4 28.84 kB/s 28.57 kB/s
5 28.86 kB/s 28.84 kB/s
---------------------------------
Average 28.81 kB/s 28.80 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.2 (KHTML, like Gecko) Chrome/5.0.342.9 Safari/533.2
This does not speed up the benchmark suite execution statistically significantly
on V8.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 28.84 kB/s 28.75 kB/s
2 28.76 kB/s 28.69 kB/s
3 28.72 kB/s 28.69 kB/s
4 28.84 kB/s 28.93 kB/s
5 28.82 kB/s 28.70 kB/s
---------------------------------
Average 28.80 kB/s 28.75 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.2 (KHTML, like Gecko)
Chrome/5.0.342.9 Safari/533.2
This does not speed up the benchmark suite execution statistically significantly
on V8.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 28.72 kB/s 28.84 kB/s
2 28.84 kB/s 28.76 kB/s
3 28.83 kB/s 28.72 kB/s
4 28.81 kB/s 28.84 kB/s
5 28.76 kB/s 28.82 kB/s
---------------------------------
Average 28.79 kB/s 28.80 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.2 (KHTML, like Gecko) Chrome/5.0.342.9 Safari/533.2
This and also speeds up the benchmark suite execution by 7.83 % on V8.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 26.17 kB/s 28.16 kB/s
2 26.05 kB/s 28.16 kB/s
3 25.99 kB/s 28.10 kB/s
4 26.13 kB/s 28.11 kB/s
5 26.14 kB/s 28.07 kB/s
---------------------------------
Average 26.10 kB/s 28.14 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.2 (KHTML, like Gecko) Chrome/5.0.342.7 Safari/533.2
This leads to simpler code and also speeds up the benchmark suite execution by
5,89 % on V8.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 24,70 kB/s 26,14 kB/s
2 24,49 kB/s 26,05 kB/s
3 24,67 kB/s 25,99 kB/s
4 24,65 kB/s 26,13 kB/s
5 24,71 kB/s 26,14 kB/s
---------------------------------
Average 24,64 kB/s 26.10 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/533.2 (KHTML, like Gecko) Chrome/5.0.342.7 Safari/533.2
The Rhino bug that prevented inclusion of \uFEFF among the whitespace characters
is no longer relevant here because we compile character classes into regexps
now, which avoids the infinite recursion.
David Majda
David Majda
Jakub Vrana
Justin Blank