patternprefix

Patternprefix is a concept used in pattern matching to describe a fixed sequence that must appear at the start of a matched input or pattern. It serves as a prefix for a subsequent pattern, constraining matches to inputs that begin with the given prefix. The term is descriptive rather than a formal standard.

How it works: In a composite pattern, the prefix is tested first. If the input does not begin with the prefix, the overall match fails. If the prefix matches, the remainder of the input is then validated against the rest of the pattern. This is common in regular expressions, template engines, and parsing systems. In regular expressions, a prefix constraint can be implemented with an explicit prefix and an anchor, for example ^prefix followed by rest. Some engines may support a separate prefix operator or token.

Examples: A regex ^cmd-.* matches strings that start with "cmd-". In a templating system, a patternprefix like "user:" might be followed by a variable part, matching inputs of the form "user:<name>". In a route-matching scheme, a fixed path prefix can route all requests under that path to a handler, e.g., a prefix "/api/" routes to API logic.

Applications: Text parsing, lexers, input validation, command parsing, and routing.

Considerations: Prefixes should be escaped to avoid unintended interpretations in regex, and case sensitivity, length, and performance can affect matching efficiency, especially with long or overlapping prefixes.