Editing Off-side rule (section)

==Implementation==

The off-side rule can be implemented in the [[lexical analysis]] phase, as in [[Python (programming language)|Python]], where increasing the indenting results in the lexer outputting an <code>INDENT</code> token, and decreasing the indenting results in the lexer outputting a <code>DEDENT</code> token.<ref>[https://docs.python.org/ Python Documentation], [https://docs.python.org/3/reference/lexical_analysis.html 2. Lexical analysis]: [https://docs.python.org/3/reference/lexical_analysis.html#indentation 2.1.8. Indentation]</ref> These tokens correspond to the opening brace <code>{</code> and closing brace <code>}</code> in languages that use braces for blocks, and means that the phrase grammar does not depend on whether braces or indentation are used. This requires that the lexer hold state, namely the current indent level, and thus can detect changes in indentation when this changes, and thus the lexical [[Formal grammar|grammar]] is not [[Context-free grammar|context-free]]: <code>INDENT</code> and <code>DEDENT</code> depend on the contextual information of the prior indent level.