Yield: Mainstream Delimited Continuations

Many mainstream languages have operators named yield that share common semantic roots but differ significantly in their details. We present the first known formal study of these mainstream yield operators, unify their many semantic differences, adapt them to to a functional setting, and distill the operational semantics and type theory for a generalized yield operator. The resultant yield, with its delimiter run, turns out to be a delimited control operator of comparable expressive power to shiftreset, with translations from one to the other. The mainstream variants of yield turn out to be one-shot or linearly used restrictions of delimited continuations. These connections may serve as a means of transporting ideas from the rich theory on delimited continuations to mainstream languages which have largely shied away from them. Dually, the restrictions of the various existing yield operations may be treated as shift-reset variants that have found mainstream acceptance and thus worthy of study.