Semantic Analysis¶

Semantic analysis is the phase of compilation or static analysis that checks the meaning of a program after its structure has been parsed. Where lexical analysis identifies tokens and parsing builds a syntax tree, semantic analysis verifies that the program makes sense according to the rules of the language.

Typical checks performed during semantic analysis include:

Type checking: verifying that values are used with compatible types
Scope resolution: ensuring that every identifier refers to a declared symbol
Arity checking: confirming that functions are called with the correct number of arguments
Constant folding: evaluating expressions whose values are known at compile time
Dead branch elimination: detecting conditions that are always true or always false

In static analysis, semantic analysis underpins the type inference and undefined-variable checks performed by tools such as PHPStan, Psalm, and Exakat.

<?php

    function greet(string $name): string {
        return 'Hello, ' . $name;
    }

    // Semantic analysis detects the type mismatch: int passed where string is expected
    greet(42);

?>

Documentation

Related packages : phpstan/phpstan, vimeo/psalm

Semantic Analysis¶

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