From e5e9ce27788135ea8dc0e1a12e3fb987b7c98f8c Mon Sep 17 00:00:00 2001
From: David Majda <david@majda.cz>
Date: Mon, 22 Oct 2012 11:37:18 +0200
Subject: [PATCH] README.md: Wrap lines at column 80

---
 README.md | 273 ++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 204 insertions(+), 69 deletions(-)

diff --git a/README.md b/README.md
index 4532c8b..4c93b69 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,10 @@
 PEG.js
 ======
 
-PEG.js is a simple parser generator for JavaScript that produces fast parsers with excellent error reporting. You can use it to process complex data or computer languages and build transformers, interpreters, compilers and other tools easily.
+PEG.js is a simple parser generator for JavaScript that produces fast parsers
+with excellent error reporting. You can use it to process complex data or
+computer languages and build transformers, interpreters, compilers and other
+tools easily.
 
 Features
 --------
@@ -9,13 +12,18 @@ Features
   * Simple and expressive grammar syntax
   * Integrates both lexical and syntactical analysis
   * Parsers have excellent error reporting out of the box
-  * Based on [parsing expression grammar](http://en.wikipedia.org/wiki/Parsing_expression_grammar) formalism — more powerful than traditional LL(*k*) and LR(*k*) parsers
-  * Usable [from your browser](http://pegjs.majda.cz/online), from the command line, or via JavaScript API
+  * Based on [parsing expression
+    grammar](http://en.wikipedia.org/wiki/Parsing_expression_grammar) formalism
+    — more powerful than traditional LL(*k*) and LR(*k*) parsers
+  * Usable [from your browser](http://pegjs.majda.cz/online), from the command
+    line, or via JavaScript API
 
 Getting Started
 ---------------
 
-[Online version](http://pegjs.majda.cz/online) is the easiest way to generate a parser. Just enter your grammar, try parsing few inputs, and download generated parser code.
+[Online version](http://pegjs.majda.cz/online) is the easiest way to generate a
+parser. Just enter your grammar, try parsing few inputs, and download generated
+parser code.
 
 Installation
 ------------
@@ -30,16 +38,20 @@ To use the JavaScript API, install PEG.js locally:
 
     $ npm install pegjs
 
-If you need both the `pegjs` command and the JavaScript API, install PEG.js both ways.
+If you need both the `pegjs` command and the JavaScript API, install PEG.js both
+ways.
 
 ### Browser
 
-[Download](http://pegjs.majda.cz/#download) the PEG.js library (regular or minified version).
+[Download](http://pegjs.majda.cz/#download) the PEG.js library (regular or
+minified version).
 
 Generating a Parser
 -------------------
 
-PEG.js generates parser from a grammar that describes expected input and can specify what the parser returns (using semantic actions on matched parts of the input). Generated parser itself is a JavaScript object with a simple API.
+PEG.js generates parser from a grammar that describes expected input and can
+specify what the parser returns (using semantic actions on matched parts of the
+input). Generated parser itself is a JavaScript object with a simple API.
 
 ### Command Line
 
@@ -47,19 +59,26 @@ To generate a parser from your grammar, use the `pegjs` command:
 
     $ pegjs arithmetics.pegjs
 
-This writes parser source code into a file with the same name as the grammar file but with “.js” extension. You can also specify the output file explicitly:
+This writes parser source code into a file with the same name as the grammar
+file but with “.js” extension. You can also specify the output file explicitly:
 
     $ pegjs arithmetics.pegjs arithmetics-parser.js
 
 If you omit both input and ouptut file, standard input and output are used.
 
-By default, the parser object is assigned to `module.exports`, which makes the output a Node.js module. You can assign it to another variable by passing a variable name using the `-e`/`--export-var` option. This may be helpful if you want to use the parser in browser environment.
+By default, the parser object is assigned to `module.exports`, which makes the
+output a Node.js module. You can assign it to another variable by passing a
+variable name using the `-e`/`--export-var` option. This may be helpful if you
+want to use the parser in browser environment.
 
 You can tweak the generated parser with several options:
 
-  * `--cache` — makes the parser cache results, avoiding exponential parsing time in pathological cases but making the parser slower
-  * `--track-line-and-column` — makes the parser track line and column (available as `line` and `column` variables in the actions and predicates)
-  * `--allowed-start-rules` — comma-separated list of rules the parser will be allowed to start parsing from (default: the first rule in the grammar)
+  * `--cache` — makes the parser cache results, avoiding exponential parsing
+    time in pathological cases but making the parser slower
+  * `--track-line-and-column` — makes the parser track line and column
+    (available as `line` and `column` variables in the actions and predicates)
+  * `--allowed-start-rules` — comma-separated list of rules the parser will be
+    allowed to start parsing from (default: the first rule in the grammar)
 
 ### JavaScript API
 
@@ -67,32 +86,47 @@ In Node.js, require the PEG.js parser generator module:
 
     var PEG = require("pegjs");
 
-In browser, include the PEG.js library in your web page or application using the `<script>` tag. The API will be available in the `PEG` global object.
+In browser, include the PEG.js library in your web page or application using the
+`<script>` tag. The API will be available in the `PEG` global object.
 
-To generate a parser, call the `PEG.buildParser` method and pass your grammar as a parameter:
+To generate a parser, call the `PEG.buildParser` method and pass your grammar as
+a parameter:
 
     var parser = PEG.buildParser("start = ('a' / 'b')+");
 
-The method will return generated parser object or throw an exception if the grammar is invalid. The exception will contain `message` property with more details about the error.
+The method will return generated parser object or throw an exception if the
+grammar is invalid. The exception will contain `message` property with more
+details about the error.
 
 To get parser’s source code, call the `toSource` method on the parser.
 
-You can tweak the generated parser by passing a second parameter with an options object to `PEG.buildParser`. The following options are supported:
+You can tweak the generated parser by passing a second parameter with an options
+object to `PEG.buildParser`. The following options are supported:
 
-  * `cache` — if `true`, makes the parser cache results, avoiding exponential parsing time in pathological cases but making the parser slower (default: `false`)
-  * `trackLineAndColumn` — if `true`, makes the parser track line and column (available as `line` and `column` variables in the actions and predicates) (default: `false`)
-  * `allowedStartRules` — rules the parser will be allowed to start parsing from (default: the first rule in the grammar)
+  * `cache` — if `true`, makes the parser cache results, avoiding exponential
+    parsing time in pathological cases but making the parser slower (default:
+    `false`)
+  * `trackLineAndColumn` — if `true`, makes the parser track line and column
+    (available as `line` and `column` variables in the actions and predicates)
+    (default: `false`)
+  * `allowedStartRules` — rules the parser will be allowed to start parsing from
+    (default: the first rule in the grammar)
 
 Using the Parser
 ----------------
 
-Using the generated parser is simple — just call its `parse` method and pass an input string as a parameter. The method will return a parse result (the exact value depends on the grammar used to build the parser) or throw an exception if the input is invalid. The exception will contain `offset`, `line`, `column`, `expected`, `found` and `message` properties with more details about the error.
+Using the generated parser is simple — just call its `parse` method and pass an
+input string as a parameter. The method will return a parse result (the exact
+value depends on the grammar used to build the parser) or throw an exception if
+the input is invalid. The exception will contain `offset`, `line`, `column`,
+`expected`, `found` and `message` properties with more details about the error.
 
     parser.parse("abba"); // returns ["a", "b", "b", "a"]
 
     parser.parse("abcd"); // throws an exception
 
-You can tweak parser behavior by passing a second parameter with an options object to the `parse` method. Only one option is currently supported:
+You can tweak parser behavior by passing a second parameter with an options
+object to the `parse` method. Only one option is currently supported:
 
   * `startRule` — name of the rule to start parsing from
 
@@ -101,9 +135,12 @@ Parsers can also support their own custom options.
 Grammar Syntax and Semantics
 ----------------------------
 
-The grammar syntax is similar to JavaScript in that it is not line-oriented and ignores whitespace between tokens. You can also use JavaScript-style comments (`// ...` and `/* ... */`).
+The grammar syntax is similar to JavaScript in that it is not line-oriented and
+ignores whitespace between tokens. You can also use JavaScript-style comments
+(`// ...` and `/* ... */`).
 
-Let's look at example grammar that recognizes simple arithmetic expressions like `2*(3+4)`. A parser generated from this grammar computes their values.
+Let's look at example grammar that recognizes simple arithmetic expressions like
+`2*(3+4)`. A parser generated from this grammar computes their values.
 
     start
       = additive
@@ -123,32 +160,69 @@ Let's look at example grammar that recognizes simple arithmetic expressions like
     integer "integer"
       = digits:[0-9]+ { return parseInt(digits.join(""), 10); }
 
-On the top level, the grammar consists of *rules* (in our example, there are five of them). Each rule has a *name* (e.g. `integer`) that identifies the rule, and a *parsing expression* (e.g. `digits:[0-9]+ { return parseInt(digits.join(""), 10); }`) that defines a pattern to match against the input text and possibly contains some JavaScript code that determines what happens when the pattern matches successfully. A rule can also contain *human-readable name* that is used in error messages (in our example, only the `integer` rule has a human-readable name). The parsing starts at the first rule, which is also called the *start rule*.
-
-A rule name must be a JavaScript identifier. It is followed by an equality sign (“=”) and a parsing expression. If the rule has a human-readable name, it is written as a JavaScript string between the name and separating equality sign. Rules need to be separated only by whitespace (their beginning is easily recognizable), but a semicolon (“;”) after the parsing expression is allowed.
-
-Rules can be preceded by an *initializer* — a piece of JavaScript code in curly braces (“{” and “}”). This code is executed before the generated parser starts parsing. All variables and functions defined in the initializer are accessible in rule actions and semantic predicates. The code inside the initializer can access options passed to the parser using the `options` variable. Curly braces in the initializer code must be balanced.
-
-The parsing expressions of the rules are used to match the input text to the grammar. There are various types of expressions — matching characters or character classes, indicating optional parts and repetition, etc. Expressions can also contain references to other rules. See detailed description below.
-
-If an expression successfully matches a part of the text when running the generated parser, it produces a *match result*, which is a JavaScript value. For example:
-
-  * An expression matching a literal string produces a JavaScript string containing matched part of the input.
-  * An expression matching repeated occurrence of some subexpression produces a JavaScript array with all the matches.
-
-The match results propagate through the rules when the rule names are used in expressions, up to the start rule. The generated parser returns start rule's match result when parsing is successful.
-
-One special case of parser expression is a *parser action* — a piece of JavaScript code inside curly braces (“{” and “}”) that takes match results of some of the the preceding expressions and returns a JavaScript value. This value is considered match result of the preceding expression (in other words, the parser action is a match result transformer).
-
-In our arithmetics example, there are many parser actions. Consider the action in expression `digits:[0-9]+ { return parseInt(digits.join(""), 10); }`. It takes the match result of the expression [0-9]+, which is an array of strings containing digits, as its parameter. It joins the digits together to form a number and converts it to a JavaScript `number` object.
+On the top level, the grammar consists of *rules* (in our example, there are
+five of them). Each rule has a *name* (e.g. `integer`) that identifies the rule,
+and a *parsing expression* (e.g. `digits:[0-9]+ { return
+parseInt(digits.join(""), 10); }`) that defines a pattern to match against the
+input text and possibly contains some JavaScript code that determines what
+happens when the pattern matches successfully. A rule can also contain
+*human-readable name* that is used in error messages (in our example, only the
+`integer` rule has a human-readable name). The parsing starts at the first rule,
+which is also called the *start rule*.
+
+A rule name must be a JavaScript identifier. It is followed by an equality sign
+(“=”) and a parsing expression. If the rule has a human-readable name, it is
+written as a JavaScript string between the name and separating equality sign.
+Rules need to be separated only by whitespace (their beginning is easily
+recognizable), but a semicolon (“;”) after the parsing expression is allowed.
+
+Rules can be preceded by an *initializer* — a piece of JavaScript code in curly
+braces (“{” and “}”). This code is executed before the generated parser starts
+parsing. All variables and functions defined in the initializer are accessible
+in rule actions and semantic predicates. The code inside the initializer can
+access options passed to the parser using the `options` variable. Curly braces
+in the initializer code must be balanced.
+
+The parsing expressions of the rules are used to match the input text to the
+grammar. There are various types of expressions — matching characters or
+character classes, indicating optional parts and repetition, etc. Expressions
+can also contain references to other rules. See detailed description below.
+
+If an expression successfully matches a part of the text when running the
+generated parser, it produces a *match result*, which is a JavaScript value. For
+example:
+
+  * An expression matching a literal string produces a JavaScript string
+    containing matched part of the input.
+  * An expression matching repeated occurrence of some subexpression produces a
+    JavaScript array with all the matches.
+
+The match results propagate through the rules when the rule names are used in
+expressions, up to the start rule. The generated parser returns start rule's
+match result when parsing is successful.
+
+One special case of parser expression is a *parser action* — a piece of
+JavaScript code inside curly braces (“{” and “}”) that takes match results of
+some of the the preceding expressions and returns a JavaScript value. This value
+is considered match result of the preceding expression (in other words, the
+parser action is a match result transformer).
+
+In our arithmetics example, there are many parser actions. Consider the action
+in expression `digits:[0-9]+ { return parseInt(digits.join(""), 10); }`. It
+takes the match result of the expression [0-9]+, which is an array of strings
+containing digits, as its parameter. It joins the digits together to form a
+number and converts it to a JavaScript `number` object.
 
 ### Parsing Expression Types
 
-There are several types of parsing expressions, some of them containing subexpressions and thus forming a recursive structure:
+There are several types of parsing expressions, some of them containing
+subexpressions and thus forming a recursive structure:
 
 #### "*literal*"<br>'*literal*'
 
-Match exact literal string and return it. The string syntax is the same as in JavaScript. Appending `i` right after the literal makes the match case-insensitive.
+Match exact literal string and return it. The string syntax is the same as in
+JavaScript. Appending `i` right after the literal makes the match
+case-insensitive.
 
 #### .
 
@@ -156,7 +230,12 @@ Match exactly one character and return it as a string.
 
 #### [*characters*]
 
-Match one character from a set and return it as a string. The characters in the list can be escaped in exactly the same way as in JavaScript string. The list of characters can also contain ranges (e.g. `[a-z]` means “all lowercase letters”). Preceding the characters with `^` inverts the matched set (e.g. `[^a-z]` means “all character but lowercase letters”). Appending `i` right after the right bracket makes the match case-insensitive.
+Match one character from a set and return it as a string. The characters in the
+list can be escaped in exactly the same way as in JavaScript string. The list of
+characters can also contain ranges (e.g. `[a-z]` means “all lowercase letters”).
+Preceding the characters with `^` inverts the matched set (e.g. `[^a-z]` means
+“all character but lowercase letters”). Appending `i` right after the right
+bracket makes the match case-insensitive.
 
 #### *rule*
 
@@ -168,80 +247,131 @@ Match a subexpression and return its match result.
 
 #### *expression* \*
 
-Match zero or more repetitions of the expression and return their match results in an array. The matching is greedy, i.e. the parser tries to match the expression as many times as possible.
+Match zero or more repetitions of the expression and return their match results
+in an array. The matching is greedy, i.e. the parser tries to match the
+expression as many times as possible.
 
 #### *expression* +
 
-Match one or more repetitions of the expression and return their match results in an array. The matching is greedy, i.e. the parser tries to match the expression as many times as possible.
+Match one or more repetitions of the expression and return their match results
+in an array. The matching is greedy, i.e. the parser tries to match the
+expression as many times as possible.
 
 #### *expression* ?
 
-Try to match the expression. If the match succeeds, return its match result, otherwise return an empty string.
+Try to match the expression. If the match succeeds, return its match result,
+otherwise return an empty string.
 
 #### & *expression*
 
-Try to match the expression. If the match succeeds, just return an empty string and do not advance the parser position, otherwise consider the match failed.
+Try to match the expression. If the match succeeds, just return an empty string
+and do not advance the parser position, otherwise consider the match failed.
 
 #### ! *expression*
 
-Try to match the expression. If the match does not succeed, just return an empty string and do not advance the parser position, otherwise consider the match failed.
+Try to match the expression. If the match does not succeed, just return an empty
+string and do not advance the parser position, otherwise consider the match
+failed.
 
 #### & { *predicate* }
 
-The predicate is a piece of JavaScript code that is executed as if it was inside a function. It gets the match results of labeled expressions in preceding expression as its arguments. It should return some JavaScript value using the `return` statement. If the returned value evaluates to `true` in boolean context, just return an empty string and do not advance the parser position; otherwise consider the match failed.
+The predicate is a piece of JavaScript code that is executed as if it was inside
+a function. It gets the match results of labeled expressions in preceding
+expression as its arguments. It should return some JavaScript value using the
+`return` statement. If the returned value evaluates to `true` in boolean
+context, just return an empty string and do not advance the parser position;
+otherwise consider the match failed.
 
-The code inside the predicate can access all variables and functions defined in the initializer at the beginning of the grammar.
+The code inside the predicate can access all variables and functions defined in
+the initializer at the beginning of the grammar.
 
-The code inside the predicate can also access the current parse position using the `offset` variable. It is a zero-based character index into the input string. If the `trackLineAndColumn` option was set to `true` when the parser was generated (or `--track-line-and-column` was used on the command line), the code can also access the current line and column using the `line` and `column` variables. Both are one-based indexes.
+The code inside the predicate can also access the current parse position using
+the `offset` variable. It is a zero-based character index into the input string.
+If the `trackLineAndColumn` option was set to `true` when the parser was
+generated (or `--track-line-and-column` was used on the command line), the code
+can also access the current line and column using the `line` and `column`
+variables. Both are one-based indexes.
 
-The code inside the predicate can also access options passed to the parser using the `options` variable.
+The code inside the predicate can also access options passed to the parser using
+the `options` variable.
 
 Note that curly braces in the predicate code must be balanced.
 
 #### ! { *predicate* }
 
-The predicate is a piece of JavaScript code that is executed as if it was inside a function. It gets the match results of labeled expressions in preceding expression as its arguments. It should return some JavaScript value using the `return` statement. If the returned value evaluates to `false` in boolean context, just return an empty string and do not advance the parser position; otherwise consider the match failed.
+The predicate is a piece of JavaScript code that is executed as if it was inside
+a function. It gets the match results of labeled expressions in preceding
+expression as its arguments. It should return some JavaScript value using the
+`return` statement. If the returned value evaluates to `false` in boolean
+context, just return an empty string and do not advance the parser position;
+otherwise consider the match failed.
 
-The code inside the predicate can access all variables and functions defined in the initializer at the beginning of the grammar.
+The code inside the predicate can access all variables and functions defined in
+the initializer at the beginning of the grammar.
 
-The code inside the predicate can also access the current parse position using the `offset` variable. It is a zero-based character index into the input string. If the `trackLineAndColumn` option was set to `true` when the parser was generated (or `--track-line-and-column` was used on the command line), the code can also access the current line and column using the `line` and `column` variables. Both are one-based indexes.
+The code inside the predicate can also access the current parse position using
+the `offset` variable. It is a zero-based character index into the input string.
+If the `trackLineAndColumn` option was set to `true` when the parser was
+generated (or `--track-line-and-column` was used on the command line), the code
+can also access the current line and column using the `line` and `column`
+variables. Both are one-based indexes.
 
-The code inside the predicate can also access options passed to the parser using the `options` variable.
+The code inside the predicate can also access options passed to the parser using
+the `options` variable.
 
 Note that curly braces in the predicate code must be balanced.
 
 #### *label* : *expression*
 
-Match the expression and remember its match result under given label. The label must be a JavaScript identifier.
+Match the expression and remember its match result under given label. The label
+must be a JavaScript identifier.
 
-Labeled expressions are useful together with actions, where saved match results can be accessed by action's JavaScript code.
+Labeled expressions are useful together with actions, where saved match results
+can be accessed by action's JavaScript code.
 
-#### *expression<sub>1</sub>* *expression<sub>2</sub>* ... *expression<sub>n</sub>*
+#### *expression<sub>1</sub>* *expression<sub>2</sub>* ...  *expression<sub>n</sub>*
 
 Match a sequence of expressions and return their match results in an array.
 
 #### *expression* { *action* }
 
-Match the expression. If the match is successful, run the action, otherwise consider the match failed.
+Match the expression. If the match is successful, run the action, otherwise
+consider the match failed.
 
-The action is a piece of JavaScript code that is executed as if it was inside a function. It gets the match results of labeled expressions in preceding expression as its arguments. The action should return some JavaScript value using the `return` statement. This value is considered match result of the preceding expression. The action can return `null` to indicate a match failure.
+The action is a piece of JavaScript code that is executed as if it was inside a
+function. It gets the match results of labeled expressions in preceding
+expression as its arguments. The action should return some JavaScript value
+using the `return` statement. This value is considered match result of the
+preceding expression. The action can return `null` to indicate a match failure.
 
-The code inside the action can access all variables and functions defined in the initializer at the beginning of the grammar. Curly braces in the action code must be balanced.
+The code inside the action can access all variables and functions defined in the
+initializer at the beginning of the grammar. Curly braces in the action code
+must be balanced.
 
-The code inside the action can also access the parse position at the beginning of the action's expression using the `offset` variable. It is a zero-based character index into the input string. If the `trackLineAndColumn` option was set to `true` when the parser was generated (or `--track-line-and-column` was used on the command line), the code can also access the line and column at the beginning of the action's expression using the `line` and `column` variables. Both are one-based indexes.
+The code inside the action can also access the parse position at the beginning
+of the action's expression using the `offset` variable. It is a zero-based
+character index into the input string. If the `trackLineAndColumn` option was
+set to `true` when the parser was generated (or `--track-line-and-column` was
+used on the command line), the code can also access the line and column at the
+beginning of the action's expression using the `line` and `column` variables.
+Both are one-based indexes.
 
-The code inside the action can also access options passed to the parser using the `options` variable.
+The code inside the action can also access options passed to the parser using
+the `options` variable.
 
 Note that curly braces in the action code must be balanced.
 
 #### *expression<sub>1</sub>* / *expression<sub>2</sub>* / ... / *expression<sub>n</sub>*
 
-Try to match the first expression, if it does not succeed, try the second one, etc. Return the match result of the first successfully matched expression. If no expression matches, consider the match failed.
+Try to match the first expression, if it does not succeed, try the second one,
+etc. Return the match result of the first successfully matched expression. If no
+expression matches, consider the match failed.
 
 Compatibility
 -------------
 
-Both the parser generator and generated parsers should run well in the following environments:
+Both the parser generator and generated parsers should run well in the following
+environments:
 
   * Node.js 0.6.6+
   * IE 8+
@@ -260,6 +390,11 @@ Development
   * [Google Group](http://groups.google.com/group/pegjs)
   * [Twitter](http://twitter.com/peg_js)
 
-PEG.js is developed by [David Majda](http://majda.cz/) ([@dmajda](http://twitter.com/dmajda)). You are welcome to contribute code. Unless your contribution is really trivial you should get in touch with me first — this can prevent wasted effort on both sides. You can send code both as a patch or a GitHub pull request.
+PEG.js is developed by [David Majda](http://majda.cz/)
+([@dmajda](http://twitter.com/dmajda)). You are welcome to contribute code.
+Unless your contribution is really trivial you should get in touch with me first
+— this can prevent wasted effort on both sides. You can send code both as a
+patch or a GitHub pull request.
 
-Note that PEG.js is still very much work in progress. There are no compatibility guarantees until version 1.0.
+Note that PEG.js is still very much work in progress. There are no compatibility
+guarantees until version 1.0.