Trait swipl::callable::OpenCall

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pub unsafe trait OpenCall: Sized {
    // Required methods
    fn next_solution(this: &Context<'_, Self>) -> PrologResult<bool>;
    fn cut(this: Context<'_, Self>);
    fn discard(this: Context<'_, Self>);
}
Expand description

An open call.

A context that wraps an open call can be asked for the next solution, or close itself through cutting the query or discarding. All these functions are actually implemented here using the OpenCall trait.

This context type is the only type where new terms are not allowed to be created, nor is it allowed to start new queries directly from this context. This is because SWI-Prolog really doesn’t like it if the prolog stack changes between solutions. It is still possible however to open a new frame and do all that stuff in the new frame. You’ll need to close the frame before continuing with solution retrieval.

Safety

A type implementing OpenCall automatically becomes a ContextType as well, so all the safety concerns regarding ContextType apply here too.

Required Methods§

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fn next_solution(this: &Context<'_, Self>) -> PrologResult<bool>

Retrieve the next solution.

If solution retrieval led to a failure or an error, this is returned in the Err part of the PrologResult. Otherwise, Ok(true) is returned if there are more solutions, and Ok(false) is returned when this is the last solution.

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fn cut(this: Context<'_, Self>)

Cut the query, keeping all data it has created.

Any unifications the query did to terms from parent contexts will be retained.

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fn discard(this: Context<'_, Self>)

Discard the query, discarding all data it has created.

Any unifications the query did to terms from parent contexts will be discarded.

Object Safety§

This trait is not object safe.

Implementors§