search: fuzzy matching via edit distance + 18 tests

editDist as an O(m*n) row-based Levenshtein DP (naive recursion is exponential
and times out under load); fuzzyTerms/fuzzyDocs/fuzzyRankTfIdf expand a term to
indexed terms within a max edit distance. 166/166.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/search/api.sx

@@ -5,7 +5,8 @@
 ;; docFreq, allTerms, tokens, positioned, evalQuery, parseQuery, searchQuery,
 ;; rankTfIdf, rankBm25, topNTfIdf, topNBm25, fedIndex, aclFilter, searchTfIdfAcl,
 ;; topNTfIdfAcl, searchBm25Acl, prefixTerms, prefixDocs, prefixRankTfIdf,
-;; paginate, pageTfIdf, pageBm25, resultCount.
+;; paginate, pageTfIdf, pageBm25, resultCount, editDist, fuzzyTerms, fuzzyDocs,
+;; fuzzyRankTfIdf.
 
 (define
   search/src
@@ -24,4 +25,6 @@
     "\n"
     search/prefix-src
     "\n"
-    search/page-src))
+    search/page-src
+    "\n"
+    search/fuzzy-src))

lib/search/conformance.conf

@@ -26,6 +26,7 @@ PRELOADS=(
   lib/search/fed.sx
   lib/search/prefix.sx
   lib/search/page.sx
+  lib/search/fuzzy.sx
   lib/search/api.sx
   lib/search/testlib.sx
 )
@@ -38,4 +39,5 @@ SUITES=(
   "integration:lib/search/tests/integration.sx"
   "prefix:lib/search/tests/prefix.sx"
   "page:lib/search/tests/page.sx"
+  "fuzzy:lib/search/tests/fuzzy.sx"
 )

lib/search/fuzzy.sx

@@ -0,0 +1,12 @@
+;; 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")

lib/search/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "search",
-  "total_passed": 148,
+  "total_passed": 166,
   "total_failed": 0,
-  "total": 148,
+  "total": 166,
   "suites": [
     {"name":"index","passed":18,"failed":0,"total":18},
     {"name":"boolean","passed":28,"failed":0,"total":28},
@@ -10,7 +10,8 @@
     {"name":"rank","passed":23,"failed":0,"total":23},
     {"name":"integration","passed":21,"failed":0,"total":21},
     {"name":"prefix","passed":14,"failed":0,"total":14},
-    {"name":"page","passed":12,"failed":0,"total":12}
+    {"name":"page","passed":12,"failed":0,"total":12},
+    {"name":"fuzzy","passed":18,"failed":0,"total":18}
   ],
-  "generated": "2026-06-06T20:54:50+00:00"
+  "generated": "2026-06-06T21:47:28+00:00"
 }

lib/search/scoreboard.md

@@ -1,6 +1,6 @@
 # search scoreboard
 
-**148 / 148 passing** (0 failure(s)).
+**166 / 166 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -11,3 +11,4 @@
 | integration | 21 | 21 | ok |
 | prefix | 14 | 14 | ok |
 | page | 12 | 12 | ok |
+| fuzzy | 18 | 18 | ok |

lib/search/tests/fuzzy.sx

@@ -0,0 +1,74 @@
+;; Extension — fuzzy matching via Levenshtein edit distance.
+;; Corpus: 1 "color flavor"  2 "colour kitten"  3 "colored"
+;; allTerms: color colored colour flavor kitten
+
+(define
+  fuzzy-setup
+  "idx = indexDoc 3 \"colored\" (indexDoc 2 \"colour kitten\" (indexDoc 1 \"color flavor\" emptyIndex))\n")
+
+(define
+  fuzzy-cases
+  (list
+    (list
+      "editDist substitution"
+      "[editDist \"kitten\" \"sitten\"]"
+      (list 1))
+    (list "editDist equal" "[editDist \"abc\" \"abc\"]" (list 0))
+    (list "editDist deletion" "[editDist \"abc\" \"ab\"]" (list 1))
+    (list "editDist insertion" "[editDist \"ab\" \"abc\"]" (list 1))
+    (list "editDist from empty" "[editDist \"\" \"abc\"]" (list 3))
+    (list "editDist both empty" "[editDist \"\" \"\"]" (list 0))
+    (list
+      "editDist classic"
+      "[editDist \"kitten\" \"sitting\"]"
+      (list 3))
+    (list
+      "editDist color colour"
+      "[editDist \"color\" \"colour\"]"
+      (list 1))
+    (list
+      "editDist color colored"
+      "[editDist \"color\" \"colored\"]"
+      (list 2))
+    (list
+      "fuzzy terms dist 1"
+      "fuzzyTerms 1 \"color\" idx"
+      (list "color" "colour"))
+    (list
+      "fuzzy terms dist 2"
+      "fuzzyTerms 2 \"color\" idx"
+      (list "color" "colored" "colour"))
+    (list "fuzzy terms exact" "fuzzyTerms 0 \"color\" idx" (list "color"))
+    (list
+      "fuzzy terms other word"
+      "fuzzyTerms 1 \"flavour\" idx"
+      (list "flavor"))
+    (list
+      "fuzzy docs dist 1"
+      "fuzzyDocs 1 \"color\" idx"
+      (list 1 2))
+    (list
+      "fuzzy docs dist 2"
+      "fuzzyDocs 2 \"color\" idx"
+      (list 1 2 3))
+    (list "fuzzy docs none" "fuzzyDocs 1 \"zzzzz\" idx" (list))
+    (list
+      "fuzzy rank dist 1"
+      "fuzzyRankTfIdf 1 \"color\" idx"
+      (list 1 2))
+    (list
+      "fuzzy rank dist 2"
+      "fuzzyRankTfIdf 2 \"color\" idx"
+      (list 1 2 3))))
+
+(define
+  fuzzy-results
+  (search-batch fuzzy-setup (map (fn (c) (nth c 1)) fuzzy-cases)))
+
+(map-indexed
+  (fn
+    (i c)
+    (hk-test (nth c 0) (nth fuzzy-results i) (nth c 2)))
+  fuzzy-cases)
+
+{:fail hk-test-fail :pass hk-test-pass :fails hk-test-fails}

plans/search-on-sx.md

@@ -111,7 +111,8 @@ lib/search/index.sx                     lib/search/eval.sx
 ## Extensions (post-roadmap, search-shaped vocabulary)
 
 - [x] prefix / wildcard queries (`prefixTerms`, `prefixDocs`, `prefixRankTfIdf`) — 14 tests
-- [ ] fuzzy matching — edit distance term expansion
+- [x] fuzzy matching — edit distance term expansion (`editDist`, `fuzzyTerms`,
+  `fuzzyDocs`, `fuzzyRankTfIdf`) — 18 tests
 - [x] result pagination (offset / limit) — `paginate`, `pageTfIdf`, `pageBm25`,
   `resultCount` — 12 tests
 - [ ] snippet / highlight generation
@@ -119,6 +120,10 @@ lib/search/index.sx                     lib/search/eval.sx
 
 ## Progress log
 
+- **Extension: fuzzy matching (166/166 total).** Levenshtein `editDist` as an O(m*n)
+  row-based DP (the naive recursive version is exponential and times out under load),
+  `fuzzyTerms`/`fuzzyDocs`/`fuzzyRankTfIdf` expand a term to indexed terms within a max
+  edit distance. 18 tests.
 - **Extension: pagination (148/148 total).** `paginate off lim` windows a ranked list
   (take lim . drop off); `pageTfIdf`/`pageBm25` + `resultCount`. 12 tests. Note the
   full conformance now runs 8 suites sequentially and needs an overall timeout ~1900s