precedencewhere

Precedencewhere is a hypothetical concept used in discussions of formal language theory and programming language design to describe a mechanism for locally adjusting operator precedence within a restricted scope. The term blends precedence, which governs how operators group in expressions, with where, signaling that the precedence rules apply only inside a defined region rather than globally.

In a language that supports precedencewhere, a precedencewhere block can be attached to a subexpression, a subgrammar, or a particular scope to specify an alternative partial order among operators for that region. The block does not alter the overall, language-wide precedence table; instead it provides a local override that guides parsing and disambiguation within the specified area. Parsing rules consult the local precedence relations when deciding how to associate operators inside the block.

Use cases for precedencewhere appear mainly in language design, domain-specific languages, and parsing research. It offers a way to resolve ambiguities or tailor syntax to specific domains without proliferating separate grammars or changing global rules. For example, in the expression a + b * c, a precedencewhere block attached to the region (b * c) could declare that plus has higher precedence than multiply within that region, yielding (a + b) * c during parsing. Such a feature can aid readability and domain convenience while preserving a clean, global grammar.

Limitations include potential confusion for readers not familiar with local overrides and the added complexity in parser implementations. Precedencewhere is closely related to ideas like scoped disambiguation, pragma-based precedence hints, and local grammar constraints. See also operator precedence, syntax disambiguation, and scope-based parsing rules.