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New lib/datalog/aggregates.sx: (count R V Goal), (sum R V Goal), (min R V Goal), (max R V Goal). dl-eval-aggregate runs dl-find-bindings on the goal under the outer subst, collects distinct values of V, applies the operator, binds R. Empty input: count/sum return 0; min/max produce no binding (rule fails). Group-by emerges naturally from outer-subst substitution into the goal — `popular(P) :- post(P), count(N, U, liked(U, P)), >=(N, 3).` counts per-post. Stratifier extended: dl-aggregate-dep-edge contributes a negation-like edge so the aggregate's goal relation is fully derived before the aggregate fires (non-monotonicity respected). Safety relaxed for aggregates: goal-internal vars are existentials, only the result var becomes bound.
315 lines
9.8 KiB
Plaintext
315 lines
9.8 KiB
Plaintext
;; lib/datalog/builtins.sx — comparison + arithmetic body literals.
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;;
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;; Built-in predicates filter / extend candidate substitutions during
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;; rule evaluation. They are not stored facts and do not participate in
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;; the Herbrand base.
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;;
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;; (< a b) (<= a b) (> a b) (>= a b) ; numeric (or string) compare
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;; (= a b) ; unify (binds vars)
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;; (!= a b) ; ground-only inequality
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;; (is X expr) ; bind X to expr's value
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;;
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;; Arithmetic expressions are SX-list compounds:
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;; (+ a b) (- a b) (* a b) (/ a b)
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;; or numbers / variables (must be bound at evaluation time).
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(define
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dl-comparison?
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(fn
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(lit)
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(and
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(list? lit)
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(> (len lit) 0)
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(let
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((rel (dl-rel-name lit)))
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(cond
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((nil? rel) false)
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(else (dl-member-string? rel (list "<" "<=" ">" ">=" "!="))))))))
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(define
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dl-eq?
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(fn
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(lit)
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(and
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(list? lit)
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(> (len lit) 0)
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(let ((rel (dl-rel-name lit))) (and (not (nil? rel)) (= rel "="))))))
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(define
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dl-is?
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(fn
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(lit)
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(and
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(list? lit)
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(> (len lit) 0)
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(let
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((rel (dl-rel-name lit)))
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(and (not (nil? rel)) (= rel "is"))))))
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;; Evaluate an arithmetic expression under subst. Returns the numeric
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;; result, or raises if any operand is unbound or non-numeric.
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(define
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dl-eval-arith
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(fn
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(expr subst)
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(let
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((w (dl-walk expr subst)))
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(cond
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((number? w) w)
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((dl-var? w)
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(error (str "datalog arith: unbound variable " (symbol->string w))))
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((list? w)
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(let
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((rel (dl-rel-name w)) (args (rest w)))
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(cond
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((not (= (len args) 2))
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(error (str "datalog arith: need 2 args, got " w)))
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(else
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(let
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((a (dl-eval-arith (first args) subst))
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(b (dl-eval-arith (nth args 1) subst)))
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(cond
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((= rel "+") (+ a b))
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((= rel "-") (- a b))
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((= rel "*") (* a b))
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((= rel "/") (/ a b))
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(else (error (str "datalog arith: unknown op " rel)))))))))
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(else (error (str "datalog arith: not a number — " w)))))))
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(define
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dl-eval-compare
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(fn
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(lit subst)
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(let
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((rel (dl-rel-name lit))
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(a (dl-walk (nth lit 1) subst))
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(b (dl-walk (nth lit 2) subst)))
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(cond
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((or (dl-var? a) (dl-var? b))
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(error
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(str
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"datalog: comparison "
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rel
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" has unbound argument; "
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"ensure prior body literal binds the variable")))
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(else
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(let
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((ok (cond ((= rel "<") (< a b)) ((= rel "<=") (<= a b)) ((= rel ">") (> a b)) ((= rel ">=") (>= a b)) ((= rel "!=") (not (dl-tuple-equal? a b))) (else (error (str "datalog: unknown compare " rel))))))
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(if ok subst nil)))))))
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(define
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dl-eval-eq
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(fn
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(lit subst)
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(dl-unify (nth lit 1) (nth lit 2) subst)))
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(define
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dl-eval-is
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(fn
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(lit subst)
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(let
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((target (nth lit 1)) (expr (nth lit 2)))
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(let
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((value (dl-eval-arith expr subst)))
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(dl-unify target value subst)))))
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(define
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dl-eval-builtin
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(fn
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(lit subst)
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(cond
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((dl-comparison? lit) (dl-eval-compare lit subst))
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((dl-eq? lit) (dl-eval-eq lit subst))
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((dl-is? lit) (dl-eval-is lit subst))
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(else (error (str "dl-eval-builtin: not a built-in: " lit))))))
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;; ── Safety analysis ──────────────────────────────────────────────
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;;
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;; Walks body literals left-to-right tracking a "bound" set. The check
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;; understands these literal kinds:
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;;
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;; positive non-built-in → adds its vars to bound
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;; (is X expr) → vars(expr) ⊆ bound, then add X (if var)
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;; <,<=,>,>=,!= → all vars ⊆ bound (no binding)
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;; (= a b) where:
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;; both non-vars → constraint check, no binding
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;; a var, b not → bind a
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;; b var, a not → bind b
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;; both vars → at least one in bound; bind the other
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;; {:neg lit} → all vars ⊆ bound (Phase 7 enforces fully)
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;;
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;; At end, head vars (minus `_`) must be ⊆ bound.
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(define
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dl-vars-not-in
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(fn
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(vs bound)
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(let
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((out (list)))
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(do
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(for-each
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(fn
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(v)
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(when (not (dl-member-string? v bound)) (append! out v)))
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vs)
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out))))
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(define
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dl-rule-check-safety
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(fn
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(rule)
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(let
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((head (get rule :head))
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(body (get rule :body))
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(bound (list))
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(err nil))
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(do
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(define
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dl-add-bound!
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(fn
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(vs)
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(for-each
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(fn
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(v)
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(when (not (dl-member-string? v bound)) (append! bound v)))
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vs)))
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(define
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dl-process-eq!
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(fn
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(lit)
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(let
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((a (nth lit 1)) (b (nth lit 2)))
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(let
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((va (dl-var? a)) (vb (dl-var? b)))
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(cond
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((and (not va) (not vb)) nil)
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((and va (not vb))
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(dl-add-bound! (list (symbol->string a))))
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((and (not va) vb)
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(dl-add-bound! (list (symbol->string b))))
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(else
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(let
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((sa (symbol->string a)) (sb (symbol->string b)))
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(cond
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((dl-member-string? sa bound)
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(dl-add-bound! (list sb)))
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((dl-member-string? sb bound)
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(dl-add-bound! (list sa)))
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(else
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(set!
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err
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(str
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"= between two unbound variables "
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(list sa sb)
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" — at least one must be bound by an "
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"earlier positive body literal")))))))))))
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(define
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dl-process-cmp!
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(fn
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(lit)
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(let
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((needed (dl-vars-of (list (nth lit 1) (nth lit 2)))))
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(let
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((missing (dl-vars-not-in needed bound)))
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(when
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(> (len missing) 0)
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(set!
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err
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(str
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"comparison "
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(dl-rel-name lit)
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" requires bound variable(s) "
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missing
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" (must be bound by an earlier positive "
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"body literal)")))))))
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(define
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dl-process-is!
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(fn
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(lit)
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(let
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((tgt (nth lit 1)) (expr (nth lit 2)))
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(let
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((needed (dl-vars-of expr)))
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(let
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((missing (dl-vars-not-in needed bound)))
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(cond
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((> (len missing) 0)
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(set!
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err
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(str
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"is RHS uses unbound variable(s) "
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missing
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" — bind them via a prior positive body "
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"literal")))
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(else
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(when
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(dl-var? tgt)
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(dl-add-bound! (list (symbol->string tgt)))))))))))
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(define
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dl-process-neg!
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(fn
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(lit)
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(let
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((needed (dl-vars-of (get lit :neg))))
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(let
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((missing (dl-vars-not-in needed bound)))
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(when
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(> (len missing) 0)
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(set!
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err
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(str
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"negation refers to unbound variable(s) "
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missing
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" — they must be bound by an earlier "
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"positive body literal")))))))
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(define
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dl-process-agg!
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(fn
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(lit)
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(let
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((result-var (nth lit 1)))
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;; Aggregate goal vars are existentially quantified within
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;; the aggregate; nothing required from outer context. The
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;; result var becomes bound after the aggregate fires.
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(when
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(dl-var? result-var)
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(dl-add-bound! (list (symbol->string result-var)))))))
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(define
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dl-process-lit!
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(fn
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(lit)
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(when
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(nil? err)
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(cond
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((and (dict? lit) (has-key? lit :neg))
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(dl-process-neg! lit))
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((dl-aggregate? lit) (dl-process-agg! lit))
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((dl-eq? lit) (dl-process-eq! lit))
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((dl-is? lit) (dl-process-is! lit))
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((dl-comparison? lit) (dl-process-cmp! lit))
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((and (list? lit) (> (len lit) 0))
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(dl-add-bound! (dl-vars-of lit)))))))
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(for-each dl-process-lit! body)
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(when
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(nil? err)
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(let
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((head-vars (dl-vars-of head)) (missing (list)))
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(do
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(for-each
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(fn
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(v)
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(when
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(and (not (dl-member-string? v bound)) (not (= v "_")))
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(append! missing v)))
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head-vars)
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(when
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(> (len missing) 0)
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(set!
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err
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(str
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"head variable(s) "
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missing
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" do not appear in any positive body literal"))))))
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err))))
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