Changewhile

Changewhile is not a formal construct in mainstream programming languages. In informal use, it denotes a class of patterns in which the termination condition of a while-like loop is altered during execution, affecting when the loop ends. The term is descriptive rather than normative and is not part of language specifications.

Across languages, changewhile can take different forms: a) the variable appearing in the loop’s condition is updated inside the loop body, so the next evaluation may pass or fail differently; or b) the condition depends on external mutable state that can be changed by other code during the loop’s lifetime. In both cases, the loop’s exit criteria evolve over time.

Illustrative example in plain text: while not done: state = update(state); if condition_met(state) then done = true. This shows how internal changes influence the condition. Note that such patterns can be harder to read and verify and may lead to nontermination if not carefully controlled.

Usage and cautions: Patterns described as changewhile are typically discouraged in favor of clearer, more explicit termination strategies. When used, they should be well documented and accompanied by invariants or termination proofs. Developers should consider alternatives such as separate state update logic, explicit break conditions, or clearly defined loop invariants to improve readability and reliability.

See also: while loop, for loop, do-while loop, termination, loop invariant.