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|
module Lookahead ( ActionTable, groupActions, current, ppActionTable
, klookahead )
where
import Grammar
import LR0
import qualified OrdUniqListSet as Set
import qualified SearchTree as FM
import SearchTree ( FM )
import MergeSort
import Prettier hiding ( concat, empty, group )
import qualified Prettier as PP
import Base
import Options
import IO
import Maybe
import Monad ( when )
type ActionTable = FM State [Action]
groupActions :: Table -> ActionTable
groupActions table = FM.fromList_C (++) [(current a, [a]) | a <- table ]
current :: Action -> State
current (Shift (s, _, _)) = s
current (Reduce Nil (s, _, _) _ _ _)
= s
current (Reduce (_ :> (_, _, s)) _ _ _ _)
= s
ppActionTable :: ActionTable -> Doc
ppActionTable table = PP.concat [ header ("State " ++ show (snumber s))
<> pretty acts <> nl <> nl
| (s, acts) <- FM.toList table ]
fixedpoint :: (Ord a, Show a, Eq v) => [a] -> ((a -> v) -> (a -> v)) -> ((a -> v) -> (a -> v))
fixedpoint dom step start = FM.unsafeLookup (lfp step' start')
where start' = FM.fromOrdList [ (a, start a) | a <- dom ]
step' fm = FM.fromOrdList [ (a, step (FM.unsafeLookup fm) a) | a <- dom ]
lfp :: (Eq a) => (a -> a) -> a -> a
lfp f a
| a == a' = a
| otherwise = lfp f a'
where a' = f a
nullableOf g = nullable (fixedpoint (nonterminals g) step start)
where start n = False
step f n = or [ nullable f (rrhs r) | r <- productionsOf g n ]
nullable f [] = True
nullable f (v : vs)
| terminal v = False
| otherwise = f v && nullable f vs
klookahead :: [Flag] -> Grammar -> GotoTable -> Table -> IO ActionTable
klookahead opts g gotoTable table'
= do verb "* Computing k-lookahead information ..."
verb (" " ++ show (sum [ 1 | n <- nonterminals g, nullable [n] ]) ++ " nullable nonterminals")
debug "e-reachable" (pretty [ (e, ereachable e) | e <- gotoTable ])
debug "reachable" (pretty [ (e, reachable e) | e <- gotoTable ])
return (fmap (map add) table)
where
pageWidth = head ([ w | Pagewidth w <- opts ] ++ [80]) `max` 40
debug s a = when (Debug `elem` opts) (hPutStr stderr t) >> return t
where t = cjustifyWith '*' pageWidth (" " ++ s++ " ") ++ "\n\n"
++ render (Page pageWidth) a ++ "\n\n"
verb = verbose opts
k = lookahead opts
table = groupActions table'
lookup s = applyWithDefault (FM.lookup table) [] s
add a@(Shift _) = a
add (Reduce st e _ p i) = Reduce st e (prune k (lainfo e)) p i
lainfo :: Edge -> Future
lainfo e@(_, _, s) = fromList [ (t, lainfo e')
| s /= errorState
, (_, _, s') <- Set.toList (reachable e)
, Shift e'@(_, t, _) <- lookup s' ]
nullable = nullableOf g
ereachable = fixedpoint gotoTable step start
where
start e = Set.empty
step f e@(_, _, s) = Set.singleton e `Set.union`
Set.unionMany [ f (s, v, goto s v)
| Item _ _ _ (v : _) _ <- toList (items s)
, nullable [v] ]
reachable = fixedpoint gotoTable step start
where
start e = Set.empty
step f e@(s0, _, s) = ereachable e `Set.union`
Set.unionMany [ f (s', v, s'')
| Item _ v (l :> _) r _ <- toList (items s)
, nullable r
, s' <- backtrack l s0
, let s'' = goto s' v
, s'' /= errorState ]
reachableWrong = fixedpoint gotoTable step start --- this is an oversimplification
where
start e = Set.empty
step f e@(s0, _, s) = Set.singleton e `Set.union`
Set.unionMany [ f (s, v, goto s v)
| Item _ _ (_ :> _) (v : _) _ <- toList (items s)
, nullable [v] ] `Set.union`
Set.unionMany [ f (s', v, s'')
| Item _ v (l :> _) [] _ <- toList (items s)
, s' <- backtrack l s0
, let s'' = goto s' v
, s'' /= errorState ]
backtrack Nil s = [ s ]
backtrack (vs :> v) s = [ x
| s' <- Set.list (invGoto v s)
, x <- backtrack vs s' ]
goto s v = applyWithDefault (FM.lookup fm) errorState (s, v)
where fm = FM.fromList [ ((si, vi), si') | (si, vi, si') <- gotoTable ]
invGoto v s' = applyWithDefault (FM.lookup fm) Set.empty (v, s')
where fm = FM.fromList_C Set.union
[ ((vi, si'), Set.singleton si) | (si, vi, si') <- gotoTable ]
errorState :: State
errorState = State 0 (Set.empty :\/ Set.empty)
oldklookahead :: [Flag] -> Int -> Table -> IO ActionTable
oldklookahead opts maxRHS table'
= do verb "* Computing k-lookahead information ..."
return (fmap (map add) table)
where
verb = verbose opts
k = lookahead opts
table = groupActions table'
lookup s = applyWithDefault (FM.lookup table) [] s
add a@(Shift _) = a
add (Reduce st e _ p i) = Reduce st e (prune k (lainfo 1 (Nil :> e))) p i
lainfo :: Int -> RevList Edge -> Future
lainfo j st0 = --if reachable /= reachable'
--then error ("LOOKAHEAD ("++ show st0 ++ "):" ++ show reachable ++ "\n" ++ show reachable')
--else
fromList [ (t, lainfo (j + 1) (st' :> e))
| st' <- Set.toList reachable
, Shift e@(_, t, _) <- lookup (cur st') ]
-- , modifier t == Copy ]
where
reachable = Set.fixedpoint forward (Set.singleton st0)
forward sts = Set.fromList
[ revTake (10*maxRHS) (nst :> e) -- prune the stack
| st <- Set.toList sts
, Reduce st' e _ _ _ <- lookup (cur st)
, nst <- matches st st' ]
{-
`Set.union` Set.fromList
[ st :> e | st <- Set.toList sts
, Shift e@(_, t, _) <- lookup (cur st)
, modifier t == Insert ]
-}
reachable' = fmap unConf $ Set.fixedpoint forward' (Set.singleton (Conf st0))
forward' sts = Set.fromList
[ Conf (nst :> e)
| Conf st <- Set.toList sts
, Reduce st' e _ _ _ <- lookup (cur st)
, nst <- matches st st' ]
cur :: RevList Edge -> State
cur Nil = impossible "current"
cur (_ :> (_, _, s)) = s
--matches st Nil e = [revTake 2 (st :> e)] -- | current st == s ]
--matches st st' e = matches' st st' e
matches :: RevList Edge -> RevList Edge -> [RevList Edge]
matches Nil _st' = [Nil]
matches st Nil = [st]
matches (st :> t) (st' :> t') = [ nst | t == t', nst <- matches st st' ]
-- | t == t' = matches st st'
-- | otherwise = []
newtype Conf = Conf { unConf :: RevList Edge }
instance Eq Conf where
Conf s1 == Conf s2 = cur s1 == cur s2
instance Ord Conf where
compare (Conf s1) (Conf s2)
= compare (cur s1) (cur s2)
|
