syntaxrules

Syntax rules are the formal constraints that determine how symbols can be arranged to form valid structures in a language. They describe the order and combination of tokens, keywords, operators, and punctuation, independent of what the structures mean (semantics). In many domains, syntax rules define the permissible arrangements that a system will accept or reject.

In programming, syntax rules are typically expressed as formal grammars. A grammar specifies production rules that define how statements, expressions, and other constructs are built from smaller parts. Context-free grammars, often written in Backus-Naur Form (BNF) or Extended BNF, are common. For example, a simple arithmetic grammar might express that an Expression can be a Term or an Expression plus a Term, and a Term can be a Factor or a Term times a Factor. Parsers use these rules to analyze source code and produce a parse tree or abstract syntax tree, which downstream components use for meaning and execution.

In natural language, syntax governs word order and hierarchical structure of phrases and clauses. Linguists describe syntax with rules and trees that capture how sentences are formed from noun phrases, verb phrases, and other constituents. While the goal and constraints differ, natural-language syntax similarly distinguishes structure from meaning, though composition and interpretation often interact in complex ways.

Applications and tooling include compilers, interpreters, linters, and formatters. Syntax errors arise when input violates the defined rules, guiding developers to correct structure rather than meaning. Syntax rules may evolve over time, affecting compatibility and tooling, and they often balance precision with readability and ambiguity management.