Revealing the underlying development principles of PHP: syntax parsing and lexical analysis

Revelation of the underlying development principles of PHP: syntax parsing and lexical analysis

Introduction:
As a scripting language widely used in Web development, the underlying development of PHP The principle has always attracted the attention of developers. Among them, syntax parsing and lexical analysis are important parts of understanding the underlying principles of PHP. This article will delve into the principles of PHP syntax parsing and lexical analysis, and help readers better understand through code examples.

1. Syntax parsing
In the underlying development of PHP, syntax parsing is the process of parsing PHP code strings into syntax trees. The grammar parser in PHP is implemented based on LR(1) grammar. Below we use a simple code example to illustrate the syntax parsing process.

Code example 1:

<?php
    $name = "John";
    echo "Hello, " . $name;
?>

1. Lexical analysis
   Before grammatical parsing, lexical analysis must first be performed. Lexical analysis splits the code string into lexical units. In the above example code, the lexical units include: variable name $name, assignment symbol =, string "John", semicolon ;wait.
2. Grammar parsing
   Grammar parsing is the process of generating a syntax tree from lexical units according to grammatical rules. In the above example code, the syntax parser parses variable declarations, variable assignments, and output operations into corresponding syntax nodes.

The following is a schematic diagram of the syntax tree generated by code example 1:

    program
    └── statement_list
        ├── statement
        │   └── assignment_statement
        │       ├── variable
        │       │   └── $name
        │       └── assignment_operator
        │           └── =
        └── statement
            └── output_statement
                └── string
                    └── "Hello, "

Through syntax analysis, the code string is converted into an abstract syntax tree to facilitate subsequent semantic analysis and implement.

2. Lexical Analysis
Lexical analysis is the process of splitting a code string into lexical units, also known as lexical scanning. The lexical analyzer in PHP uses a state machine to scan and match according to pre-defined lexical rules. Below we use a simple code example to illustrate the lexical analysis process.

Code example 2:

<?php
    function add($a, $b) {
        return $a + $b;
    }

    $result = add(1, 2);
    echo "Result is: " . $result;
?>

In code example 2, the lexical analyzer splits the code string into the following lexical units:

T_FUNCTION, T_STRING, T_VARIABLE, ',', T_VARIABLE, ')', '{', T_RETURN, T_VARIABLE, '+', T_VARIABLE, ';', '}', T_VARIABLE, '=', T_STRING, T_ENCAPSED_AND_WHITESPACE, T_CONCAT, T_VARIABLE, ';'

Where, T_FUNCTION represents the function key word, T_VARIABLE represents a variable, T_STRING represents a string, T_RETURN represents a return keyword, T_ENCAPSED_AND_WHITESPACE represents a string containing spaces, and T_CONCAT represents a string connector.

Through lexical analysis, the code string is split into meaningful lexical units to facilitate subsequent syntax analysis and execution.

Conclusion:
This article explains the principles of syntax analysis and lexical analysis of PHP, hoping that readers can have a deeper understanding of the underlying development of PHP. Syntax parsing and lexical analysis are an important part of understanding the underlying principles of PHP, and are also the basis for developing efficient and high-quality PHP applications. I hope readers can flexibly use this knowledge in future PHP development to develop more powerful PHP applications.

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