{-# LANGUAGE PatternGuards #-}

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

import PrologTools
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
	| is@(Is : _) <- q sc = maybeToList $ applyIs is ret
	| otherwise = concat $ zipWith ar (iterate next $ down sc) rs
	where
	ar sc' r = askrule sc' ret q r rs
--		| [Is, t, u] <- q sc =
--			maybeToList $ [([t], Just $ apply u ret)] `merge` ret
--		| (Is : _) <- q sc' = error "debug: Is"

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 (Rule fact _ facts notFacts) rs
--	| [Is, t, u] <- fact (next sc) = maybeToList $ [([t], Just u)] `merge` ret
	| [Is, _, _] <- fact (next sc) = error "askrule: not implemented"
	| otherwise = filter (`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 = concatMap (flip (notAsk sc0) rs . const . ($sc0)) notFacts