| Copyright | (c) wren romano 2016 |
|---|---|
| License | BSD-style |
| Maintainer | libraries@haskell.org |
| Portability | portable |
| Safe Haskell | Safe |
| Language | Haskell98 |
Data.IntMap.Merge.Lazy
Contents
Description
This module defines an API for writing functions that merge two
maps. The key functions are merge and mergeA.
Each of these can be used with several different "merge tactics".
The merge and mergeA functions are shared by
the lazy and strict modules. Only the choice of merge tactics
determines strictness. If you use mapMissing
from Data.Map.Merge.Strict then the results will be forced before
they are inserted. If you use mapMissing from
this module then they will not.
Efficiency note
The Category, Applicative, and Monad instances for WhenMissing
tactics are included because they are valid. However, they are
inefficient in many cases and should usually be avoided. The instances
for WhenMatched tactics should not pose any major efficiency problems.
Since: containers-0.5.9
Synopsis
- type SimpleWhenMissing = WhenMissing Identity
- type SimpleWhenMatched = WhenMatched Identity
- merge :: SimpleWhenMissing a c -> SimpleWhenMissing b c -> SimpleWhenMatched a b c -> IntMap a -> IntMap b -> IntMap c
- zipWithMaybeMatched :: Applicative f => (Key -> x -> y -> Maybe z) -> WhenMatched f x y z
- zipWithMatched :: Applicative f => (Key -> x -> y -> z) -> WhenMatched f x y z
- mapMaybeMissing :: Applicative f => (Key -> x -> Maybe y) -> WhenMissing f x y
- dropMissing :: Applicative f => WhenMissing f x y
- preserveMissing :: Applicative f => WhenMissing f x x
- mapMissing :: Applicative f => (Key -> x -> y) -> WhenMissing f x y
- filterMissing :: Applicative f => (Key -> x -> Bool) -> WhenMissing f x x
- data WhenMissing f x y
- data WhenMatched f x y z
- mergeA :: Applicative f => WhenMissing f a c -> WhenMissing f b c -> WhenMatched f a b c -> IntMap a -> IntMap b -> f (IntMap c)
- zipWithMaybeAMatched :: (Key -> x -> y -> f (Maybe z)) -> WhenMatched f x y z
- zipWithAMatched :: Applicative f => (Key -> x -> y -> f z) -> WhenMatched f x y z
- traverseMaybeMissing :: Applicative f => (Key -> x -> f (Maybe y)) -> WhenMissing f x y
- traverseMissing :: Applicative f => (Key -> x -> f y) -> WhenMissing f x y
- filterAMissing :: Applicative f => (Key -> x -> f Bool) -> WhenMissing f x x
- mapWhenMissing :: (Applicative f, Monad f) => (a -> b) -> WhenMissing f x a -> WhenMissing f x b
- mapWhenMatched :: Functor f => (a -> b) -> WhenMatched f x y a -> WhenMatched f x y b
- lmapWhenMissing :: (b -> a) -> WhenMissing f a x -> WhenMissing f b x
- contramapFirstWhenMatched :: (b -> a) -> WhenMatched f a y z -> WhenMatched f b y z
- contramapSecondWhenMatched :: (b -> a) -> WhenMatched f x a z -> WhenMatched f x b z
- runWhenMatched :: WhenMatched f x y z -> Key -> x -> y -> f (Maybe z)
- runWhenMissing :: WhenMissing f x y -> Key -> x -> f (Maybe y)
Simple merge tactic types
type SimpleWhenMissing = WhenMissing Identity #
A tactic for dealing with keys present in one map but not the
other in merge.
A tactic of type SimpleWhenMissing x z is an abstract
representation of a function of type Key -> x -> Maybe z.
Since: containers-0.5.9
type SimpleWhenMatched = WhenMatched Identity #
A tactic for dealing with keys present in both maps in merge.
A tactic of type SimpleWhenMatched x y z is an abstract
representation of a function of type Key -> x -> y -> Maybe z.
Since: containers-0.5.9
General combining function
Arguments
| :: SimpleWhenMissing a c | What to do with keys in |
| -> SimpleWhenMissing b c | What to do with keys in |
| -> SimpleWhenMatched a b c | What to do with keys in both |
| -> IntMap a | Map |
| -> IntMap b | Map |
| -> IntMap c |
Merge two maps.
merge takes two WhenMissing tactics, a WhenMatched tactic
and two maps. It uses the tactics to merge the maps. Its behavior
is best understood via its fundamental tactics, mapMaybeMissing
and zipWithMaybeMatched.
Consider
merge (mapMaybeMissing g1)
(mapMaybeMissing g2)
(zipWithMaybeMatched f)
m1 m2
Take, for example,
m1 = [(0,a), (1,b), (3,c), (4,d)] m2 = [(1, "one"), (2, "two"), (4, "three")]
merge will first 'align' these maps by key:
m1 = [(0,a), (1,b), (3,c), (4,d)] m2 = [(1, "one"), (2, "two"), (4, "three")]
It will then pass the individual entries and pairs of entries
to g1, g2, or f as appropriate:
maybes = [g1 0a, f 1b"one", g2 2 "two", g1 3c, f 4d"three"]
This produces a Maybe for each key:
keys = 0 1 2 3 4 results = [Nothing, Just True, Just False, Nothing, Just True]
Finally, the Just results are collected into a map:
return value = [(1, True), (2, False), (4, True)]
The other tactics below are optimizations or simplifications of
mapMaybeMissing for special cases. Most importantly,
dropMissingdrops all the keys.preserveMissingleaves all the entries alone.
When merge is given three arguments, it is inlined at the call
site. To prevent excessive inlining, you should typically use
merge to define your custom combining functions.
Examples:
unionWithKey f = merge preserveMissing preserveMissing (zipWithMatched f)
intersectionWithKey f = merge dropMissing dropMissing (zipWithMatched f)
differenceWith f = merge diffPreserve diffDrop f
symmetricDifference = merge diffPreserve diffPreserve (\ _ _ _ -> Nothing)
mapEachPiece f g h = merge (diffMapWithKey f) (diffMapWithKey g)
Since: containers-0.5.9
WhenMatched tactics
zipWithMaybeMatched :: Applicative f => (Key -> x -> y -> Maybe z) -> WhenMatched f x y z #
When a key is found in both maps, apply a function to the key and values and maybe use the result in the merged map.
zipWithMaybeMatched :: (Key -> x -> y -> Maybe z) -> SimpleWhenMatched x y z
Since: containers-0.5.9
zipWithMatched :: Applicative f => (Key -> x -> y -> z) -> WhenMatched f x y z #
When a key is found in both maps, apply a function to the key and values and use the result in the merged map.
zipWithMatched :: (Key -> x -> y -> z) -> SimpleWhenMatched x y z
Since: containers-0.5.9
WhenMissing tactics
mapMaybeMissing :: Applicative f => (Key -> x -> Maybe y) -> WhenMissing f x y #
Map over the entries whose keys are missing from the other
map, optionally removing some. This is the most powerful
SimpleWhenMissing tactic, but others are usually more efficient.
mapMaybeMissing :: (Key -> x -> Maybe y) -> SimpleWhenMissing x y
mapMaybeMissing f = traverseMaybeMissing (\k x -> pure (f k x))
but mapMaybeMissing uses fewer unnecessary Applicative
operations.
Since: containers-0.5.9
dropMissing :: Applicative f => WhenMissing f x y #
Drop all the entries whose keys are missing from the other map.
dropMissing :: SimpleWhenMissing x y
dropMissing = mapMaybeMissing (\_ _ -> Nothing)
but dropMissing is much faster.
Since: containers-0.5.9
preserveMissing :: Applicative f => WhenMissing f x x #
Preserve, unchanged, the entries whose keys are missing from the other map.
preserveMissing :: SimpleWhenMissing x x
preserveMissing = Merge.Lazy.mapMaybeMissing (\_ x -> Just x)
but preserveMissing is much faster.
Since: containers-0.5.9
mapMissing :: Applicative f => (Key -> x -> y) -> WhenMissing f x y #
Map over the entries whose keys are missing from the other map.
mapMissing :: (k -> x -> y) -> SimpleWhenMissing x y
mapMissing f = mapMaybeMissing (\k x -> Just $ f k x)
but mapMissing is somewhat faster.
Since: containers-0.5.9
filterMissing :: Applicative f => (Key -> x -> Bool) -> WhenMissing f x x #
Filter the entries whose keys are missing from the other map.
filterMissing :: (k -> x -> Bool) -> SimpleWhenMissing x x
filterMissing f = Merge.Lazy.mapMaybeMissing $ \k x -> guard (f k x) *> Just x
but this should be a little faster.
Since: containers-0.5.9
Applicative merge tactic types
data WhenMissing f x y #
A tactic for dealing with keys present in one map but not the
other in merge or mergeA.
A tactic of type WhenMissing f k x z is an abstract representation
of a function of type Key -> x -> f (Maybe z).
Since: containers-0.5.9
Instances
| (Applicative f, Monad f) => Category (WhenMissing f :: Type -> Type -> Type) # | Since: containers-0.5.9 |
Defined in Data.IntMap.Internal Methods id :: WhenMissing f a a Source # (.) :: WhenMissing f b c -> WhenMissing f a b -> WhenMissing f a c Source # | |
| (Applicative f, Monad f) => Monad (WhenMissing f x) # | Equivalent to Since: containers-0.5.9 |
Defined in Data.IntMap.Internal Methods (>>=) :: WhenMissing f x a -> (a -> WhenMissing f x b) -> WhenMissing f x b Source # (>>) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x b Source # return :: a -> WhenMissing f x a Source # fail :: String -> WhenMissing f x a Source # | |
| (Applicative f, Monad f) => Functor (WhenMissing f x) # | Since: containers-0.5.9 |
Defined in Data.IntMap.Internal Methods fmap :: (a -> b) -> WhenMissing f x a -> WhenMissing f x b Source # (<$) :: a -> WhenMissing f x b -> WhenMissing f x a Source # | |
| (Applicative f, Monad f) => Applicative (WhenMissing f x) # | Equivalent to Since: containers-0.5.9 |
Defined in Data.IntMap.Internal Methods pure :: a -> WhenMissing f x a Source # (<*>) :: WhenMissing f x (a -> b) -> WhenMissing f x a -> WhenMissing f x b Source # liftA2 :: (a -> b -> c) -> WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x c Source # (*>) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x b Source # (<*) :: WhenMissing f x a -> WhenMissing f x b -> WhenMissing f x a Source # | |
data WhenMatched f x y z #
A tactic for dealing with keys present in both maps in merge
or mergeA.
A tactic of type WhenMatched f x y z is an abstract representation
of a function of type Key -> x -> y -> f (Maybe z).
Since: containers-0.5.9
Instances
| (Monad f, Applicative f) => Category (WhenMatched f x :: Type -> Type -> Type) # | Since: containers-0.5.9 |
Defined in Data.IntMap.Internal Methods id :: WhenMatched f x a a Source # (.) :: WhenMatched f x b c -> WhenMatched f x a b -> WhenMatched f x a c Source # | |
| (Monad f, Applicative f) => Monad (WhenMatched f x y) # | Equivalent to Since: containers-0.5.9 |
Defined in Data.IntMap.Internal Methods (>>=) :: WhenMatched f x y a -> (a -> WhenMatched f x y b) -> WhenMatched f x y b Source # (>>) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y b Source # return :: a -> WhenMatched f x y a Source # fail :: String -> WhenMatched f x y a Source # | |
| Functor f => Functor (WhenMatched f x y) # | Since: containers-0.5.9 |
Defined in Data.IntMap.Internal Methods fmap :: (a -> b) -> WhenMatched f x y a -> WhenMatched f x y b Source # (<$) :: a -> WhenMatched f x y b -> WhenMatched f x y a Source # | |
| (Monad f, Applicative f) => Applicative (WhenMatched f x y) # | Equivalent to Since: containers-0.5.9 |
Defined in Data.IntMap.Internal Methods pure :: a -> WhenMatched f x y a Source # (<*>) :: WhenMatched f x y (a -> b) -> WhenMatched f x y a -> WhenMatched f x y b Source # liftA2 :: (a -> b -> c) -> WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y c Source # (*>) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y b Source # (<*) :: WhenMatched f x y a -> WhenMatched f x y b -> WhenMatched f x y a Source # | |
Applicative general combining function
Arguments
| :: Applicative f | |
| => WhenMissing f a c | What to do with keys in |
| -> WhenMissing f b c | What to do with keys in |
| -> WhenMatched f a b c | What to do with keys in both |
| -> IntMap a | Map |
| -> IntMap b | Map |
| -> f (IntMap c) |
An applicative version of merge.
mergeA takes two WhenMissing tactics, a WhenMatched
tactic and two maps. It uses the tactics to merge the maps.
Its behavior is best understood via its fundamental tactics,
traverseMaybeMissing and zipWithMaybeAMatched.
Consider
mergeA (traverseMaybeMissing g1)
(traverseMaybeMissing g2)
(zipWithMaybeAMatched f)
m1 m2
Take, for example,
m1 = [(0,a), (1,b), (3,c), (4,d)] m2 = [(1, "one"), (2, "two"), (4, "three")]
mergeA will first 'align' these maps by key:
m1 = [(0,a), (1,b), (3,c), (4,d)] m2 = [(1, "one"), (2, "two"), (4, "three")]
It will then pass the individual entries and pairs of entries
to g1, g2, or f as appropriate:
actions = [g1 0a, f 1b"one", g2 2 "two", g1 3c, f 4d"three"]
Next, it will perform the actions in the actions list in order from
left to right.
keys = 0 1 2 3 4 results = [Nothing, Just True, Just False, Nothing, Just True]
Finally, the Just results are collected into a map:
return value = [(1, True), (2, False), (4, True)]
The other tactics below are optimizations or simplifications of
traverseMaybeMissing for special cases. Most importantly,
dropMissingdrops all the keys.preserveMissingleaves all the entries alone.mapMaybeMissingdoes not use theApplicativecontext.
When mergeA is given three arguments, it is inlined at the call
site. To prevent excessive inlining, you should generally only use
mergeA to define custom combining functions.
Since: containers-0.5.9
WhenMatched tactics
zipWithMaybeAMatched :: (Key -> x -> y -> f (Maybe z)) -> WhenMatched f x y z #
When a key is found in both maps, apply a function to the key and values, perform the resulting action, and maybe use the result in the merged map.
This is the fundamental WhenMatched tactic.
Since: containers-0.5.9
zipWithAMatched :: Applicative f => (Key -> x -> y -> f z) -> WhenMatched f x y z #
When a key is found in both maps, apply a function to the key and values to produce an action and use its result in the merged map.
Since: containers-0.5.9
WhenMissing tactics
traverseMaybeMissing :: Applicative f => (Key -> x -> f (Maybe y)) -> WhenMissing f x y #
Traverse over the entries whose keys are missing from the other
map, optionally producing values to put in the result. This is
the most powerful WhenMissing tactic, but others are usually
more efficient.
Since: containers-0.5.9
traverseMissing :: Applicative f => (Key -> x -> f y) -> WhenMissing f x y #
Traverse over the entries whose keys are missing from the other map.
Since: containers-0.5.9
filterAMissing :: Applicative f => (Key -> x -> f Bool) -> WhenMissing f x x #
Filter the entries whose keys are missing from the other map
using some Applicative action.
filterAMissing f = Merge.Lazy.traverseMaybeMissing $ \k x -> (\b -> guard b *> Just x) <$> f k x
but this should be a little faster.
Since: containers-0.5.9
Covariant maps for tactics
mapWhenMissing :: (Applicative f, Monad f) => (a -> b) -> WhenMissing f x a -> WhenMissing f x b #
Map covariantly over a .WhenMissing f x
Since: containers-0.5.9
mapWhenMatched :: Functor f => (a -> b) -> WhenMatched f x y a -> WhenMatched f x y b #
Map covariantly over a .WhenMatched f x y
Since: containers-0.5.9
Contravariant maps for tactics
lmapWhenMissing :: (b -> a) -> WhenMissing f a x -> WhenMissing f b x #
Map contravariantly over a .WhenMissing f _ x
Since: containers-0.5.9
contramapFirstWhenMatched :: (b -> a) -> WhenMatched f a y z -> WhenMatched f b y z #
Map contravariantly over a .WhenMatched f _ y z
Since: containers-0.5.9
contramapSecondWhenMatched :: (b -> a) -> WhenMatched f x a z -> WhenMatched f x b z #
Map contravariantly over a .WhenMatched f x _ z
Since: containers-0.5.9
Miscellaneous tactic functions
runWhenMatched :: WhenMatched f x y z -> Key -> x -> y -> f (Maybe z) #
Along with zipWithMaybeAMatched, witnesses the isomorphism
between WhenMatched f x y z and Key -> x -> y -> f (Maybe z).
Since: containers-0.5.9
runWhenMissing :: WhenMissing f x y -> Key -> x -> f (Maybe y) #
Along with traverseMaybeMissing, witnesses the isomorphism
between WhenMissing f x y and Key -> x -> f (Maybe y).
Since: containers-0.5.9