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Document SES.hs

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Matt Diephouse 2016-01-21 10:29:52 -05:00
parent 3637bfee24
commit b8c7aaeccd
1 changed files with 6 additions and 0 deletions
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src/SES.hs
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@ -10,13 +10,18 @@ import Data.List (uncons)
import qualified Data.Map as Map
import Data.Ord (comparing)
-- | A function that maybe creates a diff from two terms.
type Compare a annotation = Term a annotation -> Term a annotation -> Maybe (Diff a annotation)
-- | A function that computes the cost of a diff.
type Cost a annotation = Diff a annotation -> Integer
-- | Find the shortest edit script (diff) between two terms given a function to compute the cost.
ses :: Compare a annotation -> Cost a annotation -> [Term a annotation] -> [Term a annotation] -> [Diff a annotation]
ses diffTerms cost as bs = fst <$> evalState diffState Map.empty where
diffState = diffAt diffTerms cost (0, 0) as bs
-- | Find the shortest edit script between two terms at a given vertex in the edit graph.
diffAt :: Compare a annotation -> Cost a annotation -> (Integer, Integer) -> [Term a annotation] -> [Term a annotation] -> State (Map.Map (Integer, Integer) [(Diff a annotation, Integer)]) [(Diff a annotation, Integer)]
diffAt _ _ _ [] [] = return []
diffAt _ cost _ [] bs = return $ foldr toInsertions [] bs where
@ -46,5 +51,6 @@ diffAt diffTerms cost (i, j) (a : as) (b : bs) = do
best = minimumBy (comparing costOf)
recur = diffAt diffTerms cost
-- | Prepend a diff to the list with the cumulative cost.
consWithCost :: Cost a annotation -> Diff a annotation -> [(Diff a annotation, Integer)] -> [(Diff a annotation, Integer)]
consWithCost cost diff rest = (diff, cost diff + maybe 0 snd (fst <$> uncons rest)) : rest