Continuations in λProlog
David Scott Warren · 1993
Continuations are well known in functional programming where they have been used to transform and compile programs. Some languages provide explicit manipulations of the continuation for the user: The user can catch and modify the current continuation. Continuations have also been used in the logic programming context to give a denotational semantics for Prolog, to generate Prolog compilers and to transform Prolog programs. In this paper, we propose to introduce new built-ins in a logic programming language to enable the user to explicitly replace the continuations. These built-ins allow the user to have a new control of the execution. We choose AProlog because of its higher-order syntax and implications in the goals which are necessary for the definition and use of these built-ins. In order to define the built-ins, we extend to λProlog the Prolog semantics based on continuations. Then, we show that an exception mechanism can be easily implemented using these new built-ins. The proposed semantics is also used to prove equivalence of goals changing the continuations.