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Languages & runtimes · #prolog
The cut operator ( ! ) is used in Prolog to control backtracking by committing to a specific choice point. While green cuts are intended to optimize performance without altering the declarative meaning, the distinction between green and red cuts becomes ambiguous when complex predicates are nested or when cuts are used to implement negation-as-failure patter
Pruning Behavior in ISO Prolog In ISO-standard Prolog implementations, the cut operator ( ! ) is used to commit the system to the current choice point, preventing backtracking to previous clauses of the same predicate. A design challenge arises when distinguishing between green cuts, which optimize performance without altering the declarative meaning, and re
The goal is to establish a clear, repeatable rule for whether a Prolog module that imports predicates from another module and then uses an unqualified export/1 clause should implicitly make those imported predicates available to downstream modules. Current implementations diverge: SWI‑Prolog treats export(_) as a blanket re‑export of all imported predicates,
Precise pruning boundary of the cut operator In ISO Prolog and major implementations such as SWI-Prolog, the cut operator ( ! ) discards choice points created since the parent goal was invoked. Unification of the clause head occurs before the cut is reached; if unification fails the cut is never executed and alternative clauses remain available. When unifica
Goal: determine whether the cut operator (!/0) should affect already‑tabled answers when evaluating a tabled predicate that contains a cut in one of its clauses. Uncertainty: XSB treats the cut as a local commitment that does not invalidate existing table entries, whereas Yap and SWI‑Prolog (with library(tabling)) may propagate the cut to prune the table, le
Standard ISO Prolog implementations typically omit the occurs check during unification to optimize performance. This behavior allows for the creation of cyclic terms, which can lead to unsoundness or infinite recursion in certain predicates. When transitioning a codebase from a permissive environment to one requiring strict logical soundness, the mechanism f
Prolog's depth-first search relies on choice points to explore all possible solutions for a goal. The cut operator ( ! ) is designed to prune these choice points to optimize performance or implement conditional logic. When implementing red cuts to create if-then-else structures, there is a risk of pruning valid paths that would otherwise be discovered throug
Saved-state deployment choice for low-traffic SWI-Prolog service Goal: minimize startup latency and resource usage for a small HTTP service by using qsave_program/2 to create a saved state and library(persistency) for fast journal reload. Uncertainty: whether to distribute a stand-alone executable that bundles the emulator or a separate state file that relie
I am writing a recursive predicate in SWI-Prolog that searches a large fact base and should commit to the first matching branch once a condition succeeds. Two documented mechanisms seem applicable: the classic cut operator ! , which prunes all remaining choice points for the clause, and the soft-cut construct Condition *-> Then ; Else , which commits only