repeatwhile

Repeatwhile is a post-conditional loop construct described in some programming language designs and in documentation as a way to repeat a block of code. In a repeatwhile loop, the loop body is executed first and the condition is evaluated after each iteration to determine whether the loop should continue. This contrasts with a standard while loop, where the condition is checked before any iteration.

If the condition evaluates to true after an iteration, the loop repeats; if false, it exits. The loop is therefore guaranteed to run at least once, unless an exception is raised or the language specifies otherwise. The behavior is closely related to do-while loops in languages that implement a post-test condition, and in some contexts is described as another naming for the same concept.

Common forms include a one-line keyword form, such as repeatwhile (condition) { statements }, or a two-part form, such as repeat { statements } while (condition). The exact syntax depends on the language and its grammar. In languages without a native repeatwhile, the same effect can be achieved with a do-while or a while loop implemented using a flag.

Advantages of repeatwhile include straightforward handling of user input prompts and simple error-checking loops, since the body is always executed before the test. Potential pitfalls include the risk of infinite loops if the condition never becomes false, and the possibility that side effects within the loop body alter the condition in unexpected ways.

Historically, repeatwhile as a distinct keyword is not present in the most widely used languages; when mentioned, it usually refers to a do-while–like construct or appears in language design discussions. Some languages implement a similar post-test loop under the name do-while or repeat-until.