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43 lines
1.6 KiB
Haskell
43 lines
1.6 KiB
Haskell
module Algorithm where
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import Control.Applicative.Free
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import Prologue hiding (Pure)
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-- | A single step in a diffing algorithm.
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--
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-- 'term' is the type of terms.
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-- 'diff' is the type of diffs.
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-- 'f' represents the continuation after diffing. Often 'Algorithm'.
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data AlgorithmF term diff f
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-- | Recursively diff two terms and pass the result to the continuation.
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= Recursive term term (diff -> f)
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-- | Diff two lists by each element’s position, and pass the resulting list of diffs to the continuation.
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| ByIndex [term] [term] ([diff] -> f)
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-- | Diff two lists by each element’s similarity and pass the resulting list of diffs to the continuation.
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| BySimilarity [term] [term] ([diff] -> f)
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deriving Functor
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-- | The free applicative for 'AlgorithmF'. This enables us to construct diff values using <$> and <*> notation.
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type Algorithm term diff = Ap (AlgorithmF term diff)
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-- | Tear down an Ap by iteration.
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iterAp :: Functor g => (g a -> a) -> Ap g a -> a
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iterAp algebra = go
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where go (Pure a) = a
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go (Ap underlying apply) = algebra (go . (apply <*>) . pure <$> underlying)
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-- DSL
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-- | Constructs a 'Recursive' diff of two terms.
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recursively :: term -> term -> Algorithm term diff diff
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recursively a b = liftAp (Recursive a b identity)
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-- | Constructs a 'ByIndex' diff of two lists of terms.
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byIndex :: [term] -> [term] -> Algorithm term diff [diff]
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byIndex a b = liftAp (ByIndex a b identity)
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-- | Constructs a 'BySimilarity' diff of two lists of terms.
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bySimilarity :: [term] -> [term] -> Algorithm term diff [diff]
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bySimilarity a b = liftAp (BySimilarity a b identity)
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