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154 lines
6.6 KiB
Haskell
154 lines
6.6 KiB
Haskell
{-# LANGUAGE DataKinds, DefaultSignatures, GADTs, RankNTypes, TypeOperators #-}
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module Algorithm where
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import Control.Applicative (liftA2)
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import Control.Monad (guard, join)
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import Control.Monad.Free.Freer
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import Data.Function (on)
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import Data.Functor.Both
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import Data.Functor.Classes
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import Data.List.NonEmpty (NonEmpty(..))
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import Data.Maybe
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import Data.Proxy
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import Data.These
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import Data.Union
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import Diff
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import GHC.Generics
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import Term
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-- | A single step in a diffing algorithm, parameterized by the types of terms, diffs, and the result of the applicable algorithm.
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data AlgorithmF term diff result where
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-- | Diff two terms with the choice of algorithm left to the interpreter’s discretion.
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Diff :: term -> term -> AlgorithmF term diff diff
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-- | Diff two terms recursively in O(n) time, resulting in a single diff node.
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Linear :: term -> term -> AlgorithmF term diff diff
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-- | Diff two lists of terms by each element’s similarity in O(n³ log n), resulting in a list of diffs.
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RWS :: [term] -> [term] -> AlgorithmF term diff [diff]
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-- | Delete a term..
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Delete :: term -> AlgorithmF term diff diff
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-- | Insert a term.
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Insert :: term -> AlgorithmF term diff diff
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-- | Replace one term with another.
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Replace :: term -> term -> AlgorithmF term diff diff
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-- | The free applicative for 'AlgorithmF'. This enables us to construct diff values using <$> and <*> notation.
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type Algorithm term diff = Freer (AlgorithmF term diff)
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-- DSL
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-- | Diff two terms without specifying the algorithm to be used.
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diff :: term -> term -> Algorithm term diff diff
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diff = (liftF .) . Algorithm.Diff
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-- | Diff a These of terms without specifying the algorithm to be used.
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diffThese :: These term term -> Algorithm term diff diff
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diffThese = these byDeleting byInserting diff
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-- | Diff a pair of optional terms without specifying the algorithm to be used.
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diffMaybe :: Maybe term -> Maybe term -> Algorithm term diff (Maybe diff)
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diffMaybe a b = case (a, b) of
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(Just a, Just b) -> Just <$> diff a b
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(Just a, _) -> Just <$> byDeleting a
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(_, Just b) -> Just <$> byInserting b
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_ -> pure Nothing
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-- | Diff two terms linearly.
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linearly :: term -> term -> Algorithm term diff diff
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linearly a b = liftF (Linear a b)
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-- | Diff two terms using RWS.
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byRWS :: [term] -> [term] -> Algorithm term diff [diff]
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byRWS a b = liftF (RWS a b)
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-- | Delete a term.
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byDeleting :: term -> Algorithm term diff diff
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byDeleting = liftF . Delete
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-- | Insert a term.
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byInserting :: term -> Algorithm term diff diff
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byInserting = liftF . Insert
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-- | Replace one term with another.
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byReplacing :: term -> term -> Algorithm term diff diff
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byReplacing = (liftF .) . Replace
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instance Show term => Show1 (AlgorithmF term diff) where
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liftShowsPrec _ _ d algorithm = case algorithm of
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Algorithm.Diff t1 t2 -> showsBinaryWith showsPrec showsPrec "Diff" d t1 t2
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Linear t1 t2 -> showsBinaryWith showsPrec showsPrec "Linear" d t1 t2
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RWS as bs -> showsBinaryWith showsPrec showsPrec "RWS" d as bs
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Delete t1 -> showsUnaryWith showsPrec "Delete" d t1
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Insert t2 -> showsUnaryWith showsPrec "Insert" d t2
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Replace t1 t2 -> showsBinaryWith showsPrec showsPrec "Replace" d t1 t2
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-- | Diff two terms based on their generic Diffable instances. If the terms are not diffable
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-- (represented by a Nothing diff returned from algorithmFor) replace one term with another.
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algorithmForTerms :: (Functor f, Diffable f) => Term f a -> Term f a -> Algorithm (Term f a) (Diff f a) (Diff f a)
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algorithmForTerms t1@(ann1 :< f1) t2@(ann2 :< f2) = fromMaybe (byReplacing t1 t2) (fmap (Diff.Diff . In (both ann1 ann2)) <$> algorithmFor f1 f2)
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-- | A type class for determining what algorithm to use for diffing two terms.
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class Diffable f where
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algorithmFor :: f term -> f term -> Maybe (Algorithm term diff (f diff))
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default algorithmFor :: (Generic1 f, Diffable' (Rep1 f)) => f term -> f term -> Maybe (Algorithm term diff (f diff))
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algorithmFor a b = fmap to1 <$> algorithmFor' (from1 a) (from1 b)
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-- | Diff a Union of Syntax terms. Left is the "rest" of the Syntax terms in the Union,
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-- Right is the "head" of the Union. 'weaken' relaxes the Union to allow the possible
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-- diff terms from the "rest" of the Union, and 'inj' adds the diff terms into the Union.
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-- NB: If Left or Right Syntax terms in our Union don't match, we fail fast by returning Nothing.
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instance Apply1 Diffable fs => Diffable (Union fs) where
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algorithmFor u1 u2 = join (apply1_2' (Proxy :: Proxy Diffable) (\ reinj f1 f2 -> fmap reinj <$> algorithmFor f1 f2) u1 u2)
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-- | Diff two list parameters using RWS.
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instance Diffable [] where
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algorithmFor a b = Just (byRWS a b)
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-- | A generic type class for diffing two terms defined by the Generic1 interface.
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class Diffable' f where
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algorithmFor' :: f term -> f term -> Maybe (Algorithm term diff (f diff))
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-- | Diff two constructors (M1 is the Generic1 newtype for meta-information (possibly related to type constructors, record selectors, and data types))
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instance Diffable' f => Diffable' (M1 i c f) where
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algorithmFor' (M1 a) (M1 b) = fmap M1 <$> algorithmFor' a b
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-- | Diff the fields of a product type.
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-- i.e. data Foo a b = Foo a b (the 'Foo a b' is captured by 'a :*: b').
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instance (Diffable' f, Diffable' g) => Diffable' (f :*: g) where
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algorithmFor' (a1 :*: b1) (a2 :*: b2) = liftA2 (:*:) <$> algorithmFor' a1 a2 <*> algorithmFor' b1 b2
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-- | Diff the constructors of a sum type.
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-- i.e. data Foo a = Foo a | Bar a (the 'Foo a' is captured by L1 and 'Bar a' is R1).
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instance (Diffable' f, Diffable' g) => Diffable' (f :+: g) where
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algorithmFor' (L1 a) (L1 b) = fmap L1 <$> algorithmFor' a b
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algorithmFor' (R1 a) (R1 b) = fmap R1 <$> algorithmFor' a b
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algorithmFor' _ _ = Nothing
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-- | Diff two parameters (Par1 is the Generic1 newtype representing a type parameter).
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-- i.e. data Foo a = Foo a (the 'a' is captured by Par1).
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instance Diffable' Par1 where
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algorithmFor' (Par1 a) (Par1 b) = Just (Par1 <$> linearly a b)
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-- | Diff two constant parameters (K1 is the Generic1 newtype representing type parameter constants).
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-- i.e. data Foo = Foo Int (the 'Int' is a constant parameter).
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instance Eq c => Diffable' (K1 i c) where
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algorithmFor' (K1 a) (K1 b) = guard (a == b) *> Just (pure (K1 a))
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-- | Diff two terms whose constructors contain 0 type parameters.
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-- i.e. data Foo = Foo.
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instance Diffable' U1 where
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algorithmFor' _ _ = Just (pure U1)
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-- | Diff two lists of parameters.
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instance Diffable' (Rec1 []) where
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algorithmFor' a b = fmap Rec1 <$> Just ((byRWS `on` unRec1) a b)
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-- | Diff two non-empty lists of parameters.
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instance Diffable' (Rec1 NonEmpty) where
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algorithmFor' (Rec1 (a:|as)) (Rec1 (b:|bs)) = Just $ do
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d:ds <- byRWS (a:as) (b:bs)
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pure (Rec1 (d :| ds))
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