;; search proximity (NEAR) — Haskell source fragment. Depends on query (posIn,
;; docsWith, sortedInter). Finds docs where two terms occur within k positions of
;; each other (unordered), using the positional postings.
;;   nearDocs :: Int -> Term -> Term -> Index -> [DocId]   (sorted)

(define
  search/near-src
  "nrAbsDiff a b = if a > b then a - b else b - a\nnrCloseTo k x [] = False\nnrCloseTo k x (y:ys) = if nrAbsDiff x y <= k then True else nrCloseTo k x ys\nnrAnyClose k [] ys = False\nnrAnyClose k (x:xs) ys = if nrCloseTo k x ys then True else nrAnyClose k xs ys\nnearInDoc k t1 t2 d idx = nrAnyClose k (posIn t1 d idx) (posIn t2 d idx)\nnearHere k t1 t2 idx d = nearInDoc k t1 t2 d idx\nnearDocs k t1 t2 idx = filter (nearHere k t1 t2 idx) (sortedInter (docsWith t1 idx) (docsWith t2 idx))\n")