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🔥 all the bounds-checking &c.

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This commit is contained in:
Rob Rix 2017-06-13 17:35:50 -04:00
parent 377e7d922f
commit 584ef4ff66
1 changed files with 4 additions and 23 deletions
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27
src/SES/Myers.hs
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@ -11,7 +11,6 @@ module SES.Myers
, MyersState(..)
) where
import Control.Exception
import qualified Data.Array as Array
import Data.Ix
import Data.Functor.Classes
@ -53,7 +52,7 @@ data Endpoint a b = Endpoint { x :: !Int, y :: !Int, script :: !(EditScript a b)
-- API
-- | Compute the shortest edit script using Myers’ algorithm.
ses :: (HasCallStack, Foldable t, Foldable u) => (a -> b -> Bool) -> t a -> u b -> EditScript a b
ses :: (Foldable t, Foldable u) => (a -> b -> Bool) -> t a -> u b -> EditScript a b
ses eq as bs = let graph = makeEditGraph as bs in evalState (runSES eq graph) (emptyStateForGraph graph)
@ -65,10 +64,8 @@ runSES eq (EditGraph as bs)
| null bs = return (This <$> toList as)
| null as = return (That <$> toList bs)
| otherwise = do
result <- for [0..(length as + length bs)] (searchUpToD . Distance)
case result of
Just (script, _) -> return (reverse script)
_ -> fail "no shortest edit script found in edit graph (this is a bug in SES.Myers)."
Just (script, _) <- for [0..(length as + length bs)] (searchUpToD . Distance)
return (reverse script)
where
-- | Search an edit graph for the shortest edit script up to a given proposed edit distance, building on the results of previous searches.
searchUpToD (Distance d) =
@ -149,16 +146,9 @@ for all run = foldr (\ a b -> (<|>) <$> run a <*> b) (return Nothing) all
{-# INLINE for #-}
-- | Throw a failure. Used to indicate an error in the implementation of Myers’ algorithm.
fail :: (HasCallStack, Monad m) => String -> m a
fail s = let ?callStack = fromCallSiteList (filter ((/= "M") . fst) (getCallStack callStack)) in
throw (MyersException s callStack)
-- | Bounds-checked indexing of arrays, preserving the call stack.
(!) :: (HasCallStack, Ix i, Show i) => Array.Array i a -> i -> a
v ! i | inRange (Array.bounds v) i = v Array.! i
| otherwise = let ?callStack = fromCallSiteList (filter ((/= "M") . fst) (getCallStack callStack)) in
throw (MyersException ("index " <> show i <> " out of bounds") callStack)
v ! i = v Array.! i
-- | Lifted showing of arrays.
@ -186,10 +176,6 @@ liftShowsEditScript sa sb _ = showListWith (liftShowsThese sa sb 0)
liftShowsEndpoint :: (Int -> a -> ShowS) -> (Int -> b -> ShowS) -> Int -> Endpoint a b -> ShowS
liftShowsEndpoint sp1 sp2 d (Endpoint x y script) = showsTernaryWith showsPrec showsPrec (liftShowsEditScript sp1 sp2) "Endpoint" d x y script
-- | Exceptions in Myers’ algorithm, along with a description and call stack.
data MyersException = MyersException String CallStack
deriving (Typeable)
-- Instances
@ -203,8 +189,3 @@ instance Show2 EditGraph where
instance Show2 Endpoint where
liftShowsPrec2 sp1 _ sp2 _ = liftShowsEndpoint sp1 sp2
instance Exception MyersException
instance Show MyersException where
showsPrec _ (MyersException s c) = showString "Exception: " . showString s . showChar '\n' . showString (prettyCallStack c)