prolog-linter-static-analysislisted

# Prolog Static Analysis & Code Quality Guidelines Use this skill to audit, lint, and analyze Prolog code for common errors, singleton variables, discontiguous clauses, non-deterministic performance issues, and non-logical constructs. ## 1. Common Linter Warnings & Remedies | Issue / Warning | Cause | Recommended Solution | | :--- | :--- | :--- | | **Singleton variables** | Variable appears only once in a clause (often a typo or unreferenced value). | Prefix with `_` (e.g. `_Var`) or use anonymous variable `_`. | | **Discontiguous predicate** | Clauses of the same predicate are separated by other predicates. | Group clauses together or add `:- discontiguous Name/Arity.` directive. | | **Unknown predicate** | Calling a predicate that has not been defined or imported. | Add `:- use_module(...)` or correct predicate name/arity. | | **Non-logical cut (`!`)** | Impure control flow masking logic bugs or disabling backtracking. | Replace with `if_/3` from `library(reif)` or pure `dif/2`. | | **Negation-as-failure (`\+/1`) for inequality** | Using `\+ (X = Y)` or `\+ Goal` to express inequality on potentially uninstantiated terms (unsound). | Replace with pure `dif(X, Y)` constraint. | | **Defaulty Representation** | Data element kinds cannot be distinguished by principal functor (forcing `var/1` or catch-all default clauses). | Wrap elements in distinct principal functors (e.g. `leaf(X)`, `node(L, R)`). Convert external defaulty data early at boundaries. | | **Mis-typed Neck Oper