29 lines
959 B
Plaintext
29 lines
959 B
Plaintext
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# Stratified negation: derive isolated nodes that have no outgoing edges.
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#
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# This example uses negation-as-failure (NOT) in a rule body. The chase
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# evaluates rules in stratified order so that Connected/1 is fully
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# materialized before Isolated/1 checks for its absence.
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#
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# NOTE: this script requires chase_stratified(), which is available via
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# the Rust API. The REPL currently runs the non-stratified chase, so
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# negation here works correctly only when the negated predicate is never
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# derived by another rule in the same stratum.
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fact Node(a).
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fact Node(b).
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fact Node(c).
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fact Node(d).
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fact Edge(a, b).
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fact Edge(b, c).
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# Copy edges to a unary Connected predicate.
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rule Edge(?X, ?Y) -> Connected(?X).
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# Nodes without outgoing edges are isolated.
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# (In the REPL's single-stratum chase this fires correctly because
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# Connected is derived from Edge, which is a base predicate.)
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rule Node(?X), NOT Connected(?X) -> Isolated(?X).
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run.
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query Isolated(?X)?
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