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|
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% %
% Frown --- An LALR(k) parser generator for Haskell 98 %
% Copyright (C) 2001-2005 Ralf Hinze %
% %
% This program is free software; you can redistribute it and/or modify %
% it under the terms of the GNU General Public License (version 2) as %
% published by the Free Software Foundation. %
% %
% This program is distributed in the hope that it will be useful, %
% but WITHOUT ANY WARRANTY; without even the implied warranty of %
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the %
% GNU General Public License for more details. %
% %
% You should have received a copy of the GNU General Public License %
% along with this program; see the file COPYING. If not, write to %
% the Free Software Foundation, Inc., 59 Temple Place - Suite 330, %
% Boston, MA 02111-1307, USA. %
% %
% Contact information %
% Email: Ralf Hinze <ralf@cs.uni-bonn.de> %
% Homepage: http://www.informatik.uni-bonn.de/~ralf/ %
% Paper mail: Dr. Ralf Hinze %
% Institut für Informatik III %
% Universität Bonn %
% Römerstraße 164 %
% 53117 Bonn, Germany %
% %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> module Case ( nexts, Branch(..) -- , caseAnalysis,
> , reportConflicts, BranchTable, branchLogic )
> where
> import Grammar hiding ( prec )
> import qualified Grammar as G
> import LR0 hiding ( fromList )
> import Lookahead
> import Future hiding ( fromList )
> import qualified OrdUniqListSet as Set
> import OrdUniqListSet ( Set )
> import qualified SearchTree as FM
> import SearchTree ( FM )
> import Prettier hiding ( concat, empty, group, stack )
> import qualified Prettier as PP
> import MergeSort
> import Base
> import Options
> import Data.Maybe
> import System.IO
> import Control.Monad
> import Data.List ( partition )
> import Prelude hiding ( lookup )
%-------------------------------= --------------------------------------------
\section{Back paths}
%-------------------------------= --------------------------------------------
A trie representing all possible paths back (the trie only contains
reduce actions).
> data Past = Node [Action] [(Edge, Past)]
> deriving (Show)
> extract :: Past -> [Action]
> extract (Node as es) = as ++ concat [ extract t | (_, t) <- es ]
> isEmpty :: Past -> Bool
> isEmpty (Node as es) = null as && and [ isEmpty t | (_, t) <- es ]
> collect :: Past -> [Action]
> collect (Node as es) = as ++ concatMap (collect . snd) es
> past :: [Action] -> Past
> past rs = fromOrdList (mergeSort [ (stack r, r) | r <- rs ])
>
> fromOrdList :: [(RevList Edge, Action)] -> Past
> fromOrdList [] = Node [] []
> fromOrdList ((Nil, r) : rs) = case fromOrdList rs of
> Node ts es -> Node (r : ts) es
> fromOrdList rs = Node [] [ (t, fromOrdList rs') | (t, rs') <- group rs ]
> group :: [(RevList Edge, Action)] -> [(Edge, [(RevList Edge, Action)])]
> group [] = []
> group ((st1 :> t1, r1) : rs1) = case group rs1 of
> [] -> [(t1, [(st1, r1)])]
> (t2, rs2) : gs
> | t1 == t2 -> (t2, (st1, r1) : rs2) : gs
> | otherwise -> (t1, [(st1, r1)]) : (t2, rs2) : gs
> group _ = impossible "Case.group"
> --group rs = error (show rs)
> lrConflict :: Past -> Bool
> lrConflict (Node [] es) = or [ lrConflict t | (_, t) <- es]
> lrConflict (Node [_] es) = or [ not (isEmpty t) | (_, t) <- es ]
> lrConflict (Node (_ : _ : _) _)
> = True
> lalrConflict :: Past -> Bool
> lalrConflict t = Set.length (Set.fromList [ pnumber a | a <- as ]) > 1
> where as = extract t
%-------------------------------= --------------------------------------------
\section{Branching structures}
%-------------------------------= --------------------------------------------
> data Branch = Shift1 Edge -- no conflict TODO: add lookahead set
> | ReduceN [Action] -- no conflict
> | ShiftReduce Edge Branch -- shift/reduce conflict
> | ReduceReduce [Action] -- reduce/reduce conflict
> | TokenCase [(Symbol, Branch)] [Branch] (Set Symbol)
> deriving (Eq, Ord, Show)
NB. |ShiftReduce| and |ReduceReduce| do not appear on the top level as
we always may use one token of lookahead. Likewise, |Shift1| does not
appear on the top level as shift actions use the lookahead. The
default branch in a `|TokenCase|' is either empty, a singleton, or a
list of error correcting shifts.
> instance Pretty Branch where
> prettyPrec d (Shift1 e) = prettyPrec d (Shift e)
> prettyPrec d (ReduceN as) = condParens (d > 9)
> $ block 4 (string "reductions (non conflicting)"
> </> intersperse nl (map pretty as))
> prettyPrec d (ShiftReduce e b)
> = condParens (d > 9)
> $ block 4 (string "*** shift/reduce conflict"
> </> pretty (Shift e)
> </> pretty b)
> prettyPrec d (ReduceReduce as)
> = condParens (d > 9)
> $ block 4 (string "*** reduce/reduce conflict"
> </> intersperse nl (map pretty as))
> prettyPrec d (TokenCase es def la)
> = condParens (d > 9)
> $ block 4 (string "case"
> </> intersperse nl [ pretty s <+> string " => " <> pretty b | (s, b) <- es ]
> </> string ("default "
> ++ (if length def > 1 then "*** error-correction conflict " else "")
> ++ "=> ") <> pretty def
> </> string "lookahead = " <> pretty la)
Order branches by symbol (this is necessary in case patterns are
overlapping).
> tokenCase :: [(Symbol, Branch)] -> [Branch] -> Set Symbol -> Branch
> tokenCase es def la = TokenCase es' def la
> where es' = mergeSortBy (\ (v1, _b1) (v2, _b2) -> number v1 <= number v2) es
Move identical branches into a default branch.
> optTokenCase :: [(Symbol, Branch)] -> [Branch] -> Set Symbol -> Branch
> optTokenCase es def la
> | null es = tokenCase es def la
> | null def && length g > 1 = tokenCase (concat gs) [snd (head g)] la
> | length def == 1 = tokenCase es' def la
> | otherwise = tokenCase es def la
> where
> g : gs = mergeSortBy leqLength (groupBy equ2 (mergeSortBy leq2 es))
> es' = filter (\ (_t, b) -> b /= head def) es
Detection of shift/reduce and reduce/reduce conflicts. Note: we can
also have shift/shift conflicts if there are several `insert'ing
shifts in a default branch.
> shiftReduce :: Branch -> Int
> shiftReduce (Shift1 _) = 0
> shiftReduce (ReduceN _) = 0
> shiftReduce (ShiftReduce _ _)
> = 1
> shiftReduce (ReduceReduce _)
> = 0
> shiftReduce (TokenCase es bs _)
> = sum [ shiftReduce t | t <- map snd es ++ bs ]
> reduceReduce :: Branch -> Int
> reduceReduce (Shift1 _) = 0
> reduceReduce (ReduceN _) = 0
> reduceReduce (ShiftReduce _ b)
> = reduceReduce b
> reduceReduce (ReduceReduce _)
> = 1
> reduceReduce (TokenCase es bs _)
> = sum [ reduceReduce t | t <- map snd es ++ bs ]
> insertInsert :: Branch -> Int
> insertInsert (Shift1 _) = 0
> insertInsert (ReduceN _) = 0
> insertInsert (ShiftReduce _ b)
> = insertInsert b
> insertInsert (ReduceReduce _)
> = 0
> insertInsert (TokenCase es bs _)
> = sum [ insertInsert t | t <- map snd es ++ bs ]
> + if length bs > 1 then 1 else 0
> reportConflicts :: Branch -> String
> reportConflicts b
> | sr > 0 && rr > 0 && ii > 0
> = ": " ++ show sr ++ " shift/reduce, " ++ show rr ++ " reduce/reduce and " ++ show ii ++ " error-correction conflicts"
> | sr > 0 && rr > 0 = ": " ++ show sr ++ " shift/reduce and " ++ show rr ++ " reduce/reduce conflicts"
> | sr > 0 && ii > 0 = ": " ++ show sr ++ " shift/reduce and " ++ show ii ++ " error-correction conflicts"
> | sr > 0 = ": " ++ show sr ++ " shift/reduce conflicts"
> | rr > 0 && ii > 0 = ": " ++ show rr ++ " reduce/reduce and " ++ show ii ++ " error-correction conflicts"
> | rr > 0 = ": " ++ show rr ++ " reduce/reduce conflicts"
> | ii > 0 = ": " ++ show ii ++ " error-correction conflicts"
> | otherwise = ""
> where sr = shiftReduce b
> rr = reduceReduce b
> ii = insertInsert b
%-------------------------------= --------------------------------------------
\section{LALR}
%-------------------------------= --------------------------------------------
> mergeLookaheads :: [Action] -> [Action]
> mergeLookaheads as = map merge as
> where
> fm = FM.fromList_C union [ (n, f) | Reduce _ _ f _ n <- as ]
> merge (Shift e) = Shift e
> merge (Reduce st e _ p n) = Reduce st e (fromJust (FM.lookup fm n)) p n
%-------------------------------= --------------------------------------------
\section{Case analysis}
%-------------------------------= --------------------------------------------
> type BranchTable = FM State Branch
> branchLogic :: [Flag] -> ActionTable -> IO BranchTable
> branchLogic opts table = do verb "* branch logic"
> when (nsr > 0) (warning (show nsr ++ " shift/reduce conflicts"))
> when (nrr > 0) (warning (show nrr ++ " reduce/reduce conflicts"))
> when (nii > 0) (warning (show nii ++ " error-correction conflicts"))
> return branchTable
> where
> verb = verbose opts
> useLALR = Code Stackless `elem` opts || Code GVStack `elem` opts
> optimize = Optimize `elem` opts
>
> branchTable = fmap caseAnalysis table
>
> nsr = sum [ shiftReduce b | (s, b) <- FM.toList branchTable ]
> nrr = sum [ reduceReduce b | (s, b) <- FM.toList branchTable ]
> nii = sum [ insertInsert b | (s, b) <- FM.toList branchTable ]
>
> caseAnalysis as
> | useLALR = b
> | optimize && reduceReduce b == 0
> = b
> | otherwise = topLevelCase opts False as' asErrCorr
> where (asErrCorr, as') = partition isErrCorr as
> b = topLevelCase opts True (mergeLookaheads as') asErrCorr
> topLevelCase :: [Flag] -> Bool -> [Action] -> [Action] -> Branch
> topLevelCase opts lalr = topLevel
> where
> conflict | lalr = lalrConflict
> | otherwise = lrConflict
>
> optimize = Optimize `elem` opts
>
> localTokenCase bs def la
> | optimize = optTokenCase bs def la
> | otherwise = tokenCase bs def la
>
> k = lookahead opts
Toplevel equations. Possibly discriminate on the lookahead token.
> topLevel :: [Action] -> [Action] -> Branch
> topLevel as asErrCorr
> | null ss && null asErrCorr && not (conflict (past rs))
> = ReduceN as -- `|as|' does not contain shifts
> | otherwise = localTokenCase
> [ (t, branch (actions t as)) | t <- Set.toList la, modifier t == Copy ]
> ([ Shift1 e | Shift e <- asErrCorr ]
> ++ [ branch (actions t as) | t <- Set.toList la, modifier t == Insert ]) la
> where
> (ss, rs) = partition isShift as
> la = nexts as
One equation for a given token. Use precedences to resolve
shift/reduce conflicts.
> branch, branch' :: [Action] -> Branch
> branch [Shift e] = Shift1 e
> branch rs@(Shift e1@(_, t1, _) : rs')
> | assoc t1 /= Unspecified && and [ prec r /= Nothing | r <- rs' ]
> = let ps = map (fromJust . prec) rs'
> in case (assoc t1, aprec (assoc t1), minimum ps, maximum ps) of
> (_, n1, nmin, nmax)
> | n1 > nmax -> Shift1 e1
> | n1 < nmin -> reduceCase rs'
> (LeftAssoc _, _, nmin, nmax)
> | nmin == nmax -> reduceCase rs'
> (RightAssoc _, _, nmin, nmax)
> | nmin == nmax -> Shift1 e1
> (NonAssoc _, _, nmin, nmax)
> -> TokenCase [] [] Set.empty -- HACK: empty `case' simulates `fail'
> _ -> branch' rs
> branch rs = branch' rs
Note that there is a good chance that all reductions have the same
precedence: all rules have a common suffix (unless there is an
explicit `|prec|' modifier). If the suffix contains a terminal, then
the rules have the precedence of the rightmost one.
> branch' (Shift e : rs') = ShiftReduce e (reduceCase rs')
> branch' rs = reduceCase rs
Discriminate on the stack to resolve reduce/reduce conflicts. Possibly
use further lookahead information.
> reduceCase :: [Action] -> Branch
> reduceCase rs = caseexpr (k - 1) (past rs)
> caseexpr :: Int -> Past -> Branch
> caseexpr j t
> | not (conflict t) = ReduceN (collect t)
> | j == 0 = ReduceReduce (collect t)
> | otherwise = localTokenCase
> [ (x, caseexpr (j - 1) (actions' x t)) | x <- Set.toList la, modifier x == Copy ]
> [ caseexpr (j - 1) (actions' x t) | x <- Set.toList la, modifier x == Insert ] la
> where la = nexts' t
> nexts :: [Action] -> Set Symbol
> nexts as = Set.unionMany [ la a | a <- as ]
> where
> la (Shift (_, t, _)) = Set.singleton t
> la (Reduce _ _ f _ _) = domain f
> actions :: Symbol -> [Action] -> [Action]
> actions x = concatMap extract
> where
> extract a@(Shift (_, t, _)) = [ a | t == x ]
> extract a@(Reduce {}) = [ a { future = f } | Just f <- [lookup (future a) x] ]
> isShift :: Action -> Bool
> isShift (Shift {}) = True
> isShift (Reduce {}) = False
More lookahead.
> nexts' :: Past -> Set Symbol
> nexts' (Node es ts) = Set.unionMany [ domain (future a) | a <- es ]
> `Set.union` Set.unionMany [ nexts' t | (_, t) <- ts ]
> actions' :: Symbol -> Past -> Past
> actions' x (Node es ts) = Node [ a{ future = f } | a <- es
> , Just f <- [lookup (future a) x] ]
> [ (e, actions' x t) | (e, t) <- ts ]
|
