Chris@0: Introduction
Chris@0: ============
Chris@0: 
Chris@17: This project is a PHP 5.2 to PHP 7.3 parser **written in PHP itself**.
Chris@0: 
Chris@0: What is this for?
Chris@0: -----------------
Chris@0: 
Chris@0: A parser is useful for [static analysis][0], manipulation of code and basically any other
Chris@0: application dealing with code programmatically. A parser constructs an [Abstract Syntax Tree][1]
Chris@0: (AST) of the code and thus allows dealing with it in an abstract and robust way.
Chris@0: 
Chris@0: There are other ways of processing source code. One that PHP supports natively is using the
Chris@0: token stream generated by [`token_get_all`][2]. The token stream is much more low level than
Chris@0: the AST and thus has different applications: It allows to also analyze the exact formatting of
Chris@0: a file. On the other hand the token stream is much harder to deal with for more complex analysis.
Chris@13: For example, an AST abstracts away the fact that, in PHP, variables can be written as `$foo`, but also
Chris@0: as `$$bar`, `${'foobar'}` or even `${!${''}=barfoo()}`. You don't have to worry about recognizing
Chris@0: all the different syntaxes from a stream of tokens.
Chris@0: 
Chris@0: Another question is: Why would I want to have a PHP parser *written in PHP*? Well, PHP might not be
Chris@0: a language especially suited for fast parsing, but processing the AST is much easier in PHP than it
Chris@0: would be in other, faster languages like C. Furthermore the people most probably wanting to do
Chris@0: programmatic PHP code analysis are incidentally PHP developers, not C developers.
Chris@0: 
Chris@0: What can it parse?
Chris@0: ------------------
Chris@0: 
Chris@17: The parser supports parsing PHP 5.2-7.3.
Chris@0: 
Chris@0: As the parser is based on the tokens returned by `token_get_all` (which is only able to lex the PHP
Chris@0: version it runs on), additionally a wrapper for emulating tokens from newer versions is provided.
Chris@17: This allows to parse PHP 7.3 source code running on PHP 7.0, for example. This emulation is somewhat
Chris@0: hacky and not perfect, but it should work well on any sane code.
Chris@0: 
Chris@0: What output does it produce?
Chris@0: ----------------------------
Chris@0: 
Chris@13: The parser produces an [Abstract Syntax Tree][1] (AST) also known as a node tree. How this looks
Chris@0: can best be seen in an example. The program `<?php echo 'Hi', 'World';` will give you a node tree
Chris@0: roughly looking like this:
Chris@0: 
Chris@0: ```
Chris@0: array(
Chris@0:     0: Stmt_Echo(
Chris@0:         exprs: array(
Chris@0:             0: Scalar_String(
Chris@0:                 value: Hi
Chris@0:             )
Chris@0:             1: Scalar_String(
Chris@0:                 value: World
Chris@0:             )
Chris@0:         )
Chris@0:     )
Chris@0: )
Chris@0: ```
Chris@0: 
Chris@0: This matches the structure of the code: An echo statement, which takes two strings as expressions,
Chris@0: with the values `Hi` and `World!`.
Chris@0: 
Chris@0: You can also see that the AST does not contain any whitespace information (but most comments are saved).
Chris@0: So using it for formatting analysis is not possible.
Chris@0: 
Chris@0: What else can it do?
Chris@0: --------------------
Chris@0: 
Chris@0: Apart from the parser itself this package also bundles support for some other, related features:
Chris@0: 
Chris@0:  * Support for pretty printing, which is the act of converting an AST into PHP code. Please note
Chris@0:    that "pretty printing" does not imply that the output is especially pretty. It's just how it's
Chris@0:    called ;)
Chris@13:  * Support for serializing and unserializing the node tree to JSON
Chris@0:  * Support for dumping the node tree in a human readable form (see the section above for an
Chris@0:    example of how the output looks like)
Chris@0:  * Infrastructure for traversing and changing the AST (node traverser and node visitors)
Chris@0:  * A node visitor for resolving namespaced names
Chris@0: 
Chris@0:  [0]: http://en.wikipedia.org/wiki/Static_program_analysis
Chris@0:  [1]: http://en.wikipedia.org/wiki/Abstract_syntax_tree
Chris@0:  [2]: http://php.net/token_get_all