module Prolog2 (
	ask,
	Fact,
--	Unify(..),
	Rule(..),
	Term(..),
	TwoD(..),
	Result
) where

import PrologTools
import Unif
import Data.Maybe

ask :: (TwoD sc, Eq sc, Eq s) =>
	sc -> Result sc s -> Fact sc s -> [Rule sc s] -> [Result sc s]
ask sc ret q rs =
	concat $ zipWith (\sc r -> askrule sc ret q r rs) (iterate next $ down sc) rs

askrule :: (TwoD sc, Eq sc, Eq s) =>
	sc -> Result sc s -> Fact sc s -> Rule sc s -> [Rule sc s] -> [Result sc s]
askrule sc ret q r@(Rule fact _ facts notFacts) rs =
	filter (flip checkAll nots) ret'
	where
	ret' = foldl (\rets (sc', f) -> rets >>= \r -> ask sc' r f rs) r0 $ zip (iterate next sc0) $
		map (const . ($ sc0)) facts
	sc0 = down sc
	r0 = case (q sc) `unification` (fact sc0) of
		Nothing -> []
		Just r0' -> maybeToList $ ret `merge` r0'
	nots = concat $ map ((flip (notAsk sc0) rs) . const . ($sc0)) notFacts