Add ability to start parsing from any grammar rule
Calling the parsing function could have been done without the ugly table
using |eval|, but this seemed to degrade performance significantly (by
about 3 %). This is probably because engines optimize badly in presence
of |eval|.
The method used in this patch does not change the benchmark suite
execution speed statistically significantly on V8.
Detailed results (benchmark suite totals):
---------------------------------
Test # Before After
---------------------------------
1 38.24 kB/s 38.28 kB/s
2 38.35 kB/s 38.15 kB/s
3 38.43 kB/s 38.40 kB/s
4 38.53 kB/s 38.20 kB/s
5 38.25 kB/s 38.39 kB/s
---------------------------------
Average 38.36 kB/s 38.39 kB/s
---------------------------------
Mozilla/5.0 (X11; U; Linux i686; en-US) AppleWebKit/534.16 (KHTML, like Gecko) Chrome/10.0.648.151 Safari/534.1
This commit is contained in:
David Majda
parent
1e57bf778d
commit
cc7ad9739f
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@ -96,6 +96,12 @@ PEG.compiler.emitter = function(ast) {
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? emit(node.initializer)
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: "";
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var parseFunctionTableItems = [];
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for (var name in node.rules) {
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parseFunctionTableItems.push(name + ": parse_" + name);
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}
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parseFunctionTableItems.sort();
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var parseFunctionDefinitions = [];
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for (var name in node.rules) {
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parseFunctionDefinitions.push(emit(node.rules[name]));
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@ -112,7 +118,19 @@ PEG.compiler.emitter = function(ast) {
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" * which the parser was generated (see |PEG.buildParser|). If the parsing is",
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" * unsuccessful, throws |PEG.parser.SyntaxError| describing the error.",
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" */",
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" parse: function(input) {",
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" parse: function(input, startRule) {",
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" var parseFunctions = {",
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" ${parseFunctionTableItems}",
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" };",
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" ",
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" if (startRule !== undefined) {",
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" if (parseFunctions[startRule] === undefined) {",
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" throw new Error(\"Invalid rule name: \" + quote(startRule) + \".\");",
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" }",
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" } else {",
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" startRule = ${startRule|string};",
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" }",
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" ",
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" var pos = 0;",
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" var reportMatchFailures = true;",
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" var rightmostMatchFailuresPos = 0;",
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@ -245,7 +263,7 @@ PEG.compiler.emitter = function(ast) {
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" ",
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" ${initializerCode}",
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" ",
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" var result = parse_${startRule}();",
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" var result = parseFunctions[startRule]();",
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" ",
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" /*",
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" * The parser is now in one of the following three states:",
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@ -302,6 +320,7 @@ PEG.compiler.emitter = function(ast) {
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"})()",
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{
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initializerCode: initializerCode,
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parseFunctionTableItems: parseFunctionTableItems.join(",\n"),
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parseFunctionDefinitions: parseFunctionDefinitions.join("\n\n"),
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startRule: node.startRule
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}
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@ -8,7 +8,73 @@ PEG.parser = (function(){
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* which the parser was generated (see |PEG.buildParser|). If the parsing is
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* unsuccessful, throws |PEG.parser.SyntaxError| describing the error.
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*/
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parse: function(input) {
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parse: function(input, startRule) {
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var parseFunctions = {
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__: parse___,
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action: parse_action,
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and: parse_and,
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braced: parse_braced,
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bracketDelimitedCharacter: parse_bracketDelimitedCharacter,
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choice: parse_choice,
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class: parse_class,
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classCharacter: parse_classCharacter,
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classCharacterRange: parse_classCharacterRange,
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colon: parse_colon,
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comment: parse_comment,
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digit: parse_digit,
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dot: parse_dot,
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doubleQuotedCharacter: parse_doubleQuotedCharacter,
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doubleQuotedLiteral: parse_doubleQuotedLiteral,
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eol: parse_eol,
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eolChar: parse_eolChar,
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eolEscapeSequence: parse_eolEscapeSequence,
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equals: parse_equals,
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grammar: parse_grammar,
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hexDigit: parse_hexDigit,
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hexEscapeSequence: parse_hexEscapeSequence,
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identifier: parse_identifier,
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initializer: parse_initializer,
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labeled: parse_labeled,
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letter: parse_letter,
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literal: parse_literal,
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lowerCaseLetter: parse_lowerCaseLetter,
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lparen: parse_lparen,
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multiLineComment: parse_multiLineComment,
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nonBraceCharacter: parse_nonBraceCharacter,
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nonBraceCharacters: parse_nonBraceCharacters,
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not: parse_not,
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plus: parse_plus,
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prefixed: parse_prefixed,
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primary: parse_primary,
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question: parse_question,
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rparen: parse_rparen,
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rule: parse_rule,
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semicolon: parse_semicolon,
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sequence: parse_sequence,
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simpleBracketDelimitedCharacter: parse_simpleBracketDelimitedCharacter,
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simpleDoubleQuotedCharacter: parse_simpleDoubleQuotedCharacter,
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simpleEscapeSequence: parse_simpleEscapeSequence,
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simpleSingleQuotedCharacter: parse_simpleSingleQuotedCharacter,
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singleLineComment: parse_singleLineComment,
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singleQuotedCharacter: parse_singleQuotedCharacter,
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singleQuotedLiteral: parse_singleQuotedLiteral,
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slash: parse_slash,
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star: parse_star,
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suffixed: parse_suffixed,
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unicodeEscapeSequence: parse_unicodeEscapeSequence,
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upperCaseLetter: parse_upperCaseLetter,
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whitespace: parse_whitespace,
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zeroEscapeSequence: parse_zeroEscapeSequence
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};
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if (startRule !== undefined) {
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if (parseFunctions[startRule] === undefined) {
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throw new Error("Invalid rule name: " + quote(startRule) + ".");
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}
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} else {
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startRule = "grammar";
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}
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var pos = 0;
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var reportMatchFailures = true;
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var rightmostMatchFailuresPos = 0;
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@ -3516,7 +3582,7 @@ PEG.parser = (function(){
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var result = parse_grammar();
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var result = parseFunctions[startRule]();
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/*
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* The parser is now in one of the following three states:
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@ -395,6 +395,28 @@ test("error positions", function() {
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doesNotParseWithPos(parser, "1\u2029x", 2, 1); // paragraph separator
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});
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test("start rule", function() {
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var parser = PEG.buildParser([
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'a = .* { return "alpha"; }',
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'b = .* { return "beta"; }'
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].join("\n"));
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/* Default start rule = the first one */
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parses(parser, "whatever", "alpha");
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/* Explicit specification of the start rule */
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parsesWithStartRule(parser, "whatever", "a", "alpha");
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parsesWithStartRule(parser, "whatever", "b", "beta");
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/* Invalid rule name */
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raises(
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function() { parser.parse("whatever", "c") },
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function(e) {
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return e instanceof Error && e.message === "Invalid rule name: \"c\".";
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}
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);
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});
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/*
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* Following examples are from Wikipedia, see
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* http://en.wikipedia.org/w/index.php?title=Parsing_expression_grammar&oldid=335106938.
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@ -2,6 +2,10 @@ parses = function(parser, input, expected) {
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deepEqual(parser.parse(input), expected);
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};
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parsesWithStartRule = function(parser, input, startRule, expected) {
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deepEqual(parser.parse(input, startRule), expected);
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};
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doesNotParse = function(parser, input) {
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raises(function() { parser.parse(input); }, parser.SyntaxError);
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};
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