Practical Parsing Patterns Special Identifier Idioms

This is the last of two columns on keywords. It covers different types of special identifiers and explores which ones should be implemented as keywords. Recall that a Keyword is just an identifier with syntactic significance. Different programming languages have different rules for when special identifiers are significant. Some of these rules have become language design idioms. This column looks at these idioms. It focuses on whether the rules suggest implementing the special identifiers as keywords or not. It addresses questions like: 1. When do the identifiers have their special meanings? 2. Does that special meaning affect parsing? 3. Are there tricks to help implement special identifiers of that type?