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Changed the flowAlgorithm function to have an error return (of type String)

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Neil Brown 2007-11-02 14:00:45 +00:00
parent 153a1823a7
commit b291901f5c
1 changed files with 22 additions and 15 deletions
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37
common/FlowAlgorithms.hs
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@ -18,6 +18,7 @@ with this program. If not, see <http://www.gnu.org/licenses/>.
module FlowAlgorithms where
import Control.Monad.Error
import qualified Data.Map as Map
import Data.Maybe
import qualified Data.Set as Set
@ -37,8 +38,7 @@ data GraphFuncs n e a = GF {
-- | Given the graph functions, a list of nodes and an entry node, performs
-- an iterative data-flow analysis.
-- TODO add an error return
flowAlgorithm :: (Ord n, Eq a) => GraphFuncs n e a -> [n] -> n -> Map.Map n a
flowAlgorithm :: (Ord n, Show n, Eq a) => GraphFuncs n e a -> [n] -> n -> Either String (Map.Map n a)
flowAlgorithm funcs nodes startNode
= iterate
(Set.fromList nonStartNodes)
@ -46,19 +46,26 @@ flowAlgorithm funcs nodes startNode
where
nonStartNodes = (filter ((/=) startNode) nodes)
foldWithMaybe :: (b -> Maybe a -> a) -> Maybe a -> [b] -> a
foldWithMaybe _ Nothing [] = error "empty list for previous nodes in flowAlgorithm" -- TODO use a better error return
foldWithMaybe _ (Just a) [] = a
foldWithMaybe f ma (b:bs) = foldWithMaybe f (Just $ f b ma) bs
foldWithMaybe :: (b -> Maybe a -> Either String a) -> Maybe a -> [b] -> Either String a
foldWithMaybe _ Nothing [] = throwError "empty list for previous nodes in flowAlgorithm"
foldWithMaybe _ (Just a) [] = return a
foldWithMaybe f ma (b:bs)
= do b' <- f b ma
foldWithMaybe f (Just b') bs
-- iterateNode :: Map.Map n a -> (n,e) -> Maybe a -> Either String a
iterateNode vals ne ma
= case Map.lookup (fst ne) vals of
Nothing -> throwError $ "Value not found for node edge: " ++ show (fst ne)
Just v -> return $ nodeFunc funcs ne v ma
-- TODO stop using fromJust, in favour of adding a more obvious error (even though fromJust should be safe here)
-- iterate :: Ord n => Set.Set n -> Map.Map n a -> Map.Map n a
-- iterate :: Ord n => Set.Set n -> Map.Map n a -> Either String (Map.Map n a)
iterate workList vals
| Set.null workList = vals
| Set.null workList = Right vals
| otherwise
= let (node, workList') = Set.deleteFindMin workList in
let total = foldWithMaybe (\ne -> nodeFunc funcs ne (fromJust $ Map.lookup (fst ne) vals)) Nothing (prevNodes funcs node) in
if total /= fromJust (Map.lookup node vals)
then iterate (workList' `Set.union` (Set.fromList $ map fst $ nextNodes funcs node)) (Map.insert node total vals)
else iterate workList' vals
= do let (node, workList') = Set.deleteFindMin workList
total <- foldWithMaybe (iterateNode vals) Nothing (prevNodes funcs node)
nodeVal <- Map.lookup node vals
if total /= nodeVal
then iterate (workList' `Set.union` (Set.fromList $ map fst $ nextNodes funcs node)) (Map.insert node total vals)
else iterate workList' vals