;; search fuzzy matching — Haskell source fragment. Depends on index + rank.
;; Levenshtein edit distance (O(m*n) row-based DP — the naive recursive version is
;; exponential and far too slow under load) expands a query term to all indexed
;; terms within a max distance, then unions / ranks their docs.
;;   editDist        :: String -> String -> Int
;;   fuzzyTerms      :: Int -> String -> Index -> [Term]   (sorted)
;;   fuzzyDocs       :: Int -> String -> Index -> [DocId]  (sorted union)
;;   fuzzyRankTfIdf  :: Int -> String -> Index -> [DocId]

(define
  search/fuzzy-src
  "edMin3 a b c = min a (min b c)\nedCost x y = if x == y then 0 else 1\nedUpto i n = if i > n then [] else i : edUpto (i + 1) n\nedLast [x] = x\nedLast (x:xs) = edLast xs\nedNrow x [] prev left = []\nedNrow x (y:ys) prev left = let v = edMin3 (head (tail prev) + 1) (left + 1) (head prev + edCost x y) in v : edNrow x ys (tail prev) v\nedRow x ys prev = let f = head prev + 1 in f : edNrow x ys prev f\nedRows [] ys prev = prev\nedRows (x:xs) ys prev = edRows xs ys (edRow x ys prev)\neditDist xs ys = edLast (edRows xs ys (edUpto 0 (length ys)))\nqWithinDist maxd term t = editDist term t <= maxd\nfuzzyTerms maxd term idx = filter (qWithinDist maxd term) (allTerms idx)\nfuzzyDocs maxd term idx = foldl (candStep idx) [] (fuzzyTerms maxd term idx)\nfuzzyRankTfIdf maxd term idx = rankTfIdf (fuzzyTerms maxd term idx) idx\n")