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+Usage of basic components
+=========================
+
+This document explains how to use the parser, the pretty printer and the node traverser.
+
+Bootstrapping
+-------------
+
+To bootstrap the library, include the autoloader generated by composer:
+
+```php
+require 'path/to/vendor/autoload.php';
+```
+
+Additionally you may want to set the `xdebug.max_nesting_level` ini option to a higher value:
+
+```php
+ini_set('xdebug.max_nesting_level', 3000);
+```
+
+This ensures that there will be no errors when traversing highly nested node trees. However, it is
+preferable to disable XDebug completely, as it can easily make this library more than five times
+slower.
+
+Parsing
+-------
+
+In order to parse code, you first have to create a parser instance:
+
+```php
+use PhpParser\ParserFactory;
+$parser = (new ParserFactory)->create(ParserFactory::PREFER_PHP7);
+```
+
+The factory accepts a kind argument, that determines how different PHP versions are treated:
+
+Kind | Behavior
+-----|---------
+`ParserFactory::PREFER_PHP7` | Try to parse code as PHP 7. If this fails, try to parse it as PHP 5.
+`ParserFactory::PREFER_PHP5` | Try to parse code as PHP 5. If this fails, try to parse it as PHP 7.
+`ParserFactory::ONLY_PHP7` | Parse code as PHP 7.
+`ParserFactory::ONLY_PHP5` | Parse code as PHP 5.
+
+Unless you have strong reason to use something else, `PREFER_PHP7` is a reasonable default.
+
+The `create()` method optionally accepts a `Lexer` instance as the second argument. Some use cases
+that require customized lexers are discussed in the [lexer documentation](component/Lexer.markdown).
+
+Subsequently you can pass PHP code (including the opening `<?php` tag) to the `parse` method in order to
+create a syntax tree. If a syntax error is encountered, an `PhpParser\Error` exception will be thrown:
+
+```php
+use PhpParser\Error;
+use PhpParser\ParserFactory;
+
+$code = '<?php // some code';
+$parser = (new ParserFactory)->create(ParserFactory::PREFER_PHP7);
+
+try {
+    $stmts = $parser->parse($code);
+    // $stmts is an array of statement nodes
+} catch (Error $e) {
+    echo 'Parse Error: ', $e->getMessage();
+}
+```
+
+A parser instance can be reused to parse multiple files.
+
+Node tree
+---------
+
+If you use the above code with `$code = "<?php echo 'Hi ', hi\\getTarget();"` the parser will
+generate a node tree looking like this:
+
+```
+array(
+    0: Stmt_Echo(
+        exprs: array(
+            0: Scalar_String(
+                value: Hi
+            )
+            1: Expr_FuncCall(
+                name: Name(
+                    parts: array(
+                        0: hi
+                        1: getTarget
+                    )
+                )
+                args: array(
+                )
+            )
+        )
+    )
+)
+```
+
+Thus `$stmts` will contain an array with only one node, with this node being an instance of
+`PhpParser\Node\Stmt\Echo_`.
+
+As PHP is a large language there are approximately 140 different nodes. In order to make work
+with them easier they are grouped into three categories:
+
+ * `PhpParser\Node\Stmt`s are statement nodes, i.e. language constructs that do not return
+   a value and can not occur in an expression. For example a class definition is a statement.
+   It doesn't return a value and you can't write something like `func(class A {});`.
+ * `PhpParser\Node\Expr`s are expression nodes, i.e. language constructs that return a value
+   and thus can occur in other expressions. Examples of expressions are `$var`
+   (`PhpParser\Node\Expr\Variable`) and `func()` (`PhpParser\Node\Expr\FuncCall`).
+ * `PhpParser\Node\Scalar`s are nodes representing scalar values, like `'string'`
+   (`PhpParser\Node\Scalar\String_`), `0` (`PhpParser\Node\Scalar\LNumber`) or magic constants
+   like `__FILE__` (`PhpParser\Node\Scalar\MagicConst\File`). All `PhpParser\Node\Scalar`s extend
+   `PhpParser\Node\Expr`, as scalars are expressions, too.
+ * There are some nodes not in either of these groups, for example names (`PhpParser\Node\Name`)
+   and call arguments (`PhpParser\Node\Arg`).
+
+Some node class names have a trailing `_`. This is used whenever the class name would otherwise clash
+with a PHP keyword.
+
+Every node has a (possibly zero) number of subnodes. You can access subnodes by writing
+`$node->subNodeName`. The `Stmt\Echo_` node has only one subnode `exprs`. So in order to access it
+in the above example you would write `$stmts[0]->exprs`. If you wanted to access the name of the function
+call, you would write `$stmts[0]->exprs[1]->name`.
+
+All nodes also define a `getType()` method that returns the node type. The type is the class name
+without the `PhpParser\Node\` prefix and `\` replaced with `_`. It also does not contain a trailing
+`_` for reserved-keyword class names.
+
+It is possible to associate custom metadata with a node using the `setAttribute()` method. This data
+can then be retrieved using `hasAttribute()`, `getAttribute()` and `getAttributes()`.
+
+By default the lexer adds the `startLine`, `endLine` and `comments` attributes. `comments` is an array
+of `PhpParser\Comment[\Doc]` instances.
+
+The start line can also be accessed using `getLine()`/`setLine()` (instead of `getAttribute('startLine')`).
+The last doc comment from the `comments` attribute can be obtained using `getDocComment()`.
+
+Pretty printer
+--------------
+
+The pretty printer component compiles the AST back to PHP code. As the parser does not retain formatting
+information the formatting is done using a specified scheme. Currently there is only one scheme available,
+namely `PhpParser\PrettyPrinter\Standard`.
+
+```php
+use PhpParser\Error;
+use PhpParser\ParserFactory;
+use PhpParser\PrettyPrinter;
+
+$code = "<?php echo 'Hi ', hi\\getTarget();";
+
+$parser = (new ParserFactory)->create(ParserFactory::PREFER_PHP7);
+$prettyPrinter = new PrettyPrinter\Standard;
+
+try {
+    // parse
+    $stmts = $parser->parse($code);
+
+    // change
+    $stmts[0]         // the echo statement
+          ->exprs     // sub expressions
+          [0]         // the first of them (the string node)
+          ->value     // it's value, i.e. 'Hi '
+          = 'Hello '; // change to 'Hello '
+
+    // pretty print
+    $code = $prettyPrinter->prettyPrint($stmts);
+
+    echo $code;
+} catch (Error $e) {
+    echo 'Parse Error: ', $e->getMessage();
+}
+```
+
+The above code will output:
+
+    <?php echo 'Hello ', hi\getTarget();
+
+As you can see the source code was first parsed using `PhpParser\Parser->parse()`, then changed and then
+again converted to code using `PhpParser\PrettyPrinter\Standard->prettyPrint()`.
+
+The `prettyPrint()` method pretty prints a statements array. It is also possible to pretty print only a
+single expression using `prettyPrintExpr()`.
+
+The `prettyPrintFile()` method can be used to print an entire file. This will include the opening `<?php` tag
+and handle inline HTML as the first/last statement more gracefully.
+
+Node traversation
+-----------------
+
+The above pretty printing example used the fact that the source code was known and thus it was easy to
+write code that accesses a certain part of a node tree and changes it. Normally this is not the case.
+Usually you want to change / analyze code in a generic way, where you don't know how the node tree is
+going to look like.
+
+For this purpose the parser provides a component for traversing and visiting the node tree. The basic
+structure of a program using this `PhpParser\NodeTraverser` looks like this:
+
+```php
+use PhpParser\NodeTraverser;
+use PhpParser\ParserFactory;
+use PhpParser\PrettyPrinter;
+
+$parser        = (new ParserFactory)->create(ParserFactory::PREFER_PHP7);
+$traverser     = new NodeTraverser;
+$prettyPrinter = new PrettyPrinter\Standard;
+
+// add your visitor
+$traverser->addVisitor(new MyNodeVisitor);
+
+try {
+    $code = file_get_contents($fileName);
+
+    // parse
+    $stmts = $parser->parse($code);
+
+    // traverse
+    $stmts = $traverser->traverse($stmts);
+
+    // pretty print
+    $code = $prettyPrinter->prettyPrintFile($stmts);
+
+    echo $code;
+} catch (PhpParser\Error $e) {
+    echo 'Parse Error: ', $e->getMessage();
+}
+```
+
+The corresponding node visitor might look like this:
+
+```php
+use PhpParser\Node;
+use PhpParser\NodeVisitorAbstract;
+
+class MyNodeVisitor extends NodeVisitorAbstract
+{
+    public function leaveNode(Node $node) {
+        if ($node instanceof Node\Scalar\String_) {
+            $node->value = 'foo';
+        }
+    }
+}
+```
+
+The above node visitor would change all string literals in the program to `'foo'`.
+
+All visitors must implement the `PhpParser\NodeVisitor` interface, which defines the following four
+methods:
+
+```php
+public function beforeTraverse(array $nodes);
+public function enterNode(\PhpParser\Node $node);
+public function leaveNode(\PhpParser\Node $node);
+public function afterTraverse(array $nodes);
+```
+
+The `beforeTraverse()` method is called once before the traversal begins and is passed the nodes the
+traverser was called with. This method can be used for resetting values before traversation or
+preparing the tree for traversal.
+
+The `afterTraverse()` method is similar to the `beforeTraverse()` method, with the only difference that
+it is called once after the traversal.
+
+The `enterNode()` and `leaveNode()` methods are called on every node, the former when it is entered,
+i.e. before its subnodes are traversed, the latter when it is left.
+
+All four methods can either return the changed node or not return at all (i.e. `null`) in which
+case the current node is not changed.
+
+The `enterNode()` method can additionally return the value `NodeTraverser::DONT_TRAVERSE_CHILDREN`,
+which instructs the traverser to skip all children of the current node.
+
+The `leaveNode()` method can additionally return the value `NodeTraverser::REMOVE_NODE`, in which
+case the current node will be removed from the parent array. Furthermore it is possible to return
+an array of nodes, which will be merged into the parent array at the offset of the current node.
+I.e. if in `array(A, B, C)` the node `B` should be replaced with `array(X, Y, Z)` the result will
+be `array(A, X, Y, Z, C)`.
+
+Instead of manually implementing the `NodeVisitor` interface you can also extend the `NodeVisitorAbstract`
+class, which will define empty default implementations for all the above methods.
+
+The NameResolver node visitor
+-----------------------------
+
+One visitor is already bundled with the package: `PhpParser\NodeVisitor\NameResolver`. This visitor
+helps you work with namespaced code by trying to resolve most names to fully qualified ones.
+
+For example, consider the following code:
+
+    use A as B;
+    new B\C();
+
+In order to know that `B\C` really is `A\C` you would need to track aliases and namespaces yourself.
+The `NameResolver` takes care of that and resolves names as far as possible.
+
+After running it most names will be fully qualified. The only names that will stay unqualified are
+unqualified function and constant names. These are resolved at runtime and thus the visitor can't
+know which function they are referring to. In most cases this is a non-issue as the global functions
+are meant.
+
+Also the `NameResolver` adds a `namespacedName` subnode to class, function and constant declarations
+that contains the namespaced name instead of only the shortname that is available via `name`.
+
+Example: Converting namespaced code to pseudo namespaces
+--------------------------------------------------------
+
+A small example to understand the concept: We want to convert namespaced code to pseudo namespaces
+so it works on 5.2, i.e. names like `A\\B` should be converted to `A_B`. Note that such conversions
+are fairly complicated if you take PHP's dynamic features into account, so our conversion will
+assume that no dynamic features are used.
+
+We start off with the following base code:
+
+```php
+use PhpParser\ParserFactory;
+use PhpParser\PrettyPrinter;
+use PhpParser\NodeTraverser;
+use PhpParser\NodeVisitor\NameResolver;
+
+$inDir  = '/some/path';
+$outDir = '/some/other/path';
+
+$parser        = (new ParserFactory)->create(ParserFactory::PREFER_PHP7);
+$traverser     = new NodeTraverser;
+$prettyPrinter = new PrettyPrinter\Standard;
+
+$traverser->addVisitor(new NameResolver); // we will need resolved names
+$traverser->addVisitor(new NamespaceConverter); // our own node visitor
+
+// iterate over all .php files in the directory
+$files = new \RecursiveIteratorIterator(new \RecursiveDirectoryIterator($inDir));
+$files = new \RegexIterator($files, '/\.php$/');
+
+foreach ($files as $file) {
+    try {
+        // read the file that should be converted
+        $code = file_get_contents($file);
+
+        // parse
+        $stmts = $parser->parse($code);
+
+        // traverse
+        $stmts = $traverser->traverse($stmts);
+
+        // pretty print
+        $code = $prettyPrinter->prettyPrintFile($stmts);
+
+        // write the converted file to the target directory
+        file_put_contents(
+            substr_replace($file->getPathname(), $outDir, 0, strlen($inDir)),
+            $code
+        );
+    } catch (PhpParser\Error $e) {
+        echo 'Parse Error: ', $e->getMessage();
+    }
+}
+```
+
+Now lets start with the main code, the `NodeVisitor\NamespaceConverter`. One thing it needs to do
+is convert `A\\B` style names to `A_B` style ones.
+
+```php
+use PhpParser\Node;
+
+class NamespaceConverter extends \PhpParser\NodeVisitorAbstract
+{
+    public function leaveNode(Node $node) {
+        if ($node instanceof Node\Name) {
+            return new Node\Name($node->toString('_'));
+        }
+    }
+}
+```
+
+The above code profits from the fact that the `NameResolver` already resolved all names as far as
+possible, so we don't need to do that. We only need to create a string with the name parts separated
+by underscores instead of backslashes. This is what `$node->toString('_')` does. (If you want to
+create a name with backslashes either write `$node->toString()` or `(string) $node`.) Then we create
+a new name from the string and return it. Returning a new node replaces the old node.
+
+Another thing we need to do is change the class/function/const declarations. Currently they contain
+only the shortname (i.e. the last part of the name), but they need to contain the complete name including
+the namespace prefix:
+
+```php
+use PhpParser\Node;
+use PhpParser\Node\Stmt;
+
+class NodeVisitor_NamespaceConverter extends \PhpParser\NodeVisitorAbstract
+{
+    public function leaveNode(Node $node) {
+        if ($node instanceof Node\Name) {
+            return new Node\Name($node->toString('_'));
+        } elseif ($node instanceof Stmt\Class_
+                  || $node instanceof Stmt\Interface_
+                  || $node instanceof Stmt\Function_) {
+            $node->name = $node->namespacedName->toString('_');
+        } elseif ($node instanceof Stmt\Const_) {
+            foreach ($node->consts as $const) {
+                $const->name = $const->namespacedName->toString('_');
+            }
+        }
+    }
+}
+```
+
+There is not much more to it than converting the namespaced name to string with `_` as separator.
+
+The last thing we need to do is remove the `namespace` and `use` statements:
+
+```php
+use PhpParser\Node;
+use PhpParser\Node\Stmt;
+
+class NodeVisitor_NamespaceConverter extends \PhpParser\NodeVisitorAbstract
+{
+    public function leaveNode(Node $node) {
+        if ($node instanceof Node\Name) {
+            return new Node\Name($node->toString('_'));
+        } elseif ($node instanceof Stmt\Class_
+                  || $node instanceof Stmt\Interface_
+                  || $node instanceof Stmt\Function_) {
+            $node->name = $node->namespacedName->toString('_');
+        } elseif ($node instanceof Stmt\Const_) {
+            foreach ($node->consts as $const) {
+                $const->name = $const->namespacedName->toString('_');
+            }
+        } elseif ($node instanceof Stmt\Namespace_) {
+            // returning an array merges is into the parent array
+            return $node->stmts;
+        } elseif ($node instanceof Stmt\Use_) {
+            // returning false removed the node altogether
+            return false;
+        }
+    }
+}
+```
+
+That's all.