Editing Formal language (section)

=== Programming languages ===
{{Main|Syntax (programming languages)|Compiler-compiler}}

A compiler usually has two distinct components. A [[lexical analyzer]], sometimes generated by a tool like [[lex programming tool|<code>lex</code>]], identifies the tokens of the programming language grammar, e.g. [[identifier]]s or [[Keyword (computer programming)|keywords]], numeric and string literals, punctuation and operator symbols, which are themselves specified by a simpler formal language, usually by means of [[regular expressions]]. At the most basic conceptual level, a [[parser]], sometimes generated by a [[parser generator]] like <code>[[yacc]]</code>, attempts to decide if the source program is syntactically valid, that is if it is well formed with respect to the programming language grammar for which the compiler was built.

Of course, compilers do more than just parse the source code – they usually translate it into some executable format. Because of this, a parser usually outputs more than a yes/no answer, typically an [[abstract syntax tree]]. This is used by subsequent stages of the compiler to eventually generate an [[executable]] containing [[machine code]] that runs directly on the hardware, or some [[intermediate code]] that requires a [[virtual machine]] to execute.