;; search query AST + boolean/phrase evaluation — Haskell source fragment.
;; Depends on tokenize + index.
;;   data Query = Term String | And Query Query | Or Query Query
;;              | Not Query | Phrase [String]
;;   evalQuery :: Index -> Query -> [DocId]   (sorted, unique)
;; Boolean ops are linear merges over docid-sorted posting lists; Not uses
;; allDocs as the universe; Phrase checks positional adjacency.

(define
  search/query-src
  "data Query = Term String | And Query Query | Or Query Query | Not Query | Phrase [String]\ndocsWith t idx = map fst (lookupTerm t idx)\nsortedUnion [] ys = ys\nsortedUnion xs [] = xs\nsortedUnion (x:xs) (y:ys) = if x < y then x : sortedUnion xs (y:ys) else if x > y then y : sortedUnion (x:xs) ys else x : sortedUnion xs ys\nsortedInter [] ys = []\nsortedInter xs [] = []\nsortedInter (x:xs) (y:ys) = if x < y then sortedInter xs (y:ys) else if x > y then sortedInter (x:xs) ys else x : sortedInter xs ys\nsortedDiff [] ys = []\nsortedDiff xs [] = xs\nsortedDiff (x:xs) (y:ys) = if x < y then x : sortedDiff xs (y:ys) else if x > y then sortedDiff (x:xs) ys else sortedDiff xs ys\nmergeDocs acc e = sortedUnion acc (map fst (snd e))\nallDocs idx = foldl mergeDocs [] idx\nposIn t d idx = case lookup d (lookupTerm t idx) of { Nothing -> []; Just ps -> ps }\nelemSorted x [] = False\nelemSorted x (y:ys) = if x == y then True else if x < y then False else elemSorted x ys\nphraseAtAll [] d idx p i = True\nphraseAtAll (t:ts) d idx p i = if elemSorted (p + i) (posIn t d idx) then phraseAtAll ts d idx p (i + 1) else False\nphraseStartsAt ts d idx p = phraseAtAll ts d idx p 0\nphraseInDoc [] d idx = True\nphraseInDoc (t0:rest) d idx = any (phraseStartsAt (t0:rest) d idx) (posIn t0 d idx)\nphraseHere ts idx d = phraseInDoc ts d idx\ninterStep idx acc tt = sortedInter acc (docsWith tt idx)\nphraseCands [] idx = allDocs idx\nphraseCands (t:ts) idx = foldl (interStep idx) (docsWith t idx) ts\nphraseDocs ts idx = filter (phraseHere ts idx) (phraseCands ts idx)\nevalQuery idx q = case q of { Term t -> docsWith t idx ; And a b -> sortedInter (evalQuery idx a) (evalQuery idx b) ; Or a b -> sortedUnion (evalQuery idx a) (evalQuery idx b) ; Not a -> sortedDiff (allDocs idx) (evalQuery idx a) ; Phrase ts -> phraseDocs ts idx }\n")
