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Add a merge function to compute a Term from a Diff.

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This commit is contained in:
Rob Rix 2016-06-27 12:37:27 -04:00
parent 3f6cab2abc
commit 9829d2df84
1 changed files with 6 additions and 0 deletions
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6
src/Diff.hs
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@ -24,6 +24,12 @@ diffSum patchCost diff = sum $ fmap patchCost diff
diffCost :: Diff a annotation -> Integer
diffCost = diffSum $ patchSum termSize
merge :: (Patch (Term leaf annotation) -> Term leaf annotation) -> Diff leaf annotation -> Term leaf annotation
merge transform = cata algebra . fmap transform
where algebra :: FreeF (CofreeF (Syntax leaf) (Both annotation)) (Term leaf annotation) (Term leaf annotation) -> Term leaf annotation
algebra (Pure p) = p
algebra (Free (annotations :< syntax)) = cofree (Both.fst annotations :< syntax)
beforeTerm :: Diff leaf annotation -> Maybe (Term leaf annotation)
beforeTerm = cata algebra
where algebra :: FreeF (CofreeF (Syntax leaf) (Both annotation)) (Patch (Term leaf annotation)) (Maybe (Term leaf annotation)) -> Maybe (Term leaf annotation)