@jahed/sparql-engine/dist/operators/modifiers/ask.js

SPARQL query engine for servers and web browsers.

import { Pipeline } from "../../engine/pipeline/pipeline.js";
import { BindingBase, Bindings } from "../../rdf/bindings.js";
/**
 * A AskOperator output True if a source iterator has solutions, false otherwise.
 * results are outputed following the SPARQL XML results format
 * @see {@link https://www.w3.org/TR/2013/REC-sparql11-query-20130321/#ask}
 * @param source - Source {@link PipelineStage}
 * @return A {@link PipelineStage} that evaluate the ASK modifier
 */
export default function ask(source) {
    const defaultValue = new BindingBase();
    const engine = Pipeline.getInstance();
    let op = engine.defaultValues(source, defaultValue);
    op = engine.first(op);
    return engine.map(op, (b) => b.size > 0);
}
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