Copyright | (c) David Feuer 2016 |
---|---|
License | BSD-style |
Maintainer | libraries@haskell.org |
Portability | portable |
Safe Haskell | Safe |
Language | Haskell98 |
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 this module then the results will be forced before they are
inserted. If you use mapMissing
from
Data.Map.Merge.Lazy then they will not.
preserveMissing
inconsistency
For historical reasons, the preserved values are /not/ forced. To force
them, use preserveMissing'
.
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 :: Ord k => SimpleWhenMissing k a c -> SimpleWhenMissing k b c -> SimpleWhenMatched k a b c -> Map k a -> Map k b -> Map k c
- zipWithMaybeMatched :: Applicative f => (k -> x -> y -> Maybe z) -> WhenMatched f k x y z
- zipWithMatched :: Applicative f => (k -> x -> y -> z) -> WhenMatched f k x y z
- mapMaybeMissing :: Applicative f => (k -> x -> Maybe y) -> WhenMissing f k x y
- dropMissing :: Applicative f => WhenMissing f k x y
- preserveMissing :: Applicative f => WhenMissing f k x x
- preserveMissing' :: Applicative f => WhenMissing f k x x
- mapMissing :: Applicative f => (k -> x -> y) -> WhenMissing f k x y
- filterMissing :: Applicative f => (k -> x -> Bool) -> WhenMissing f k x x
- data WhenMissing f k x y
- data WhenMatched f k x y z
- mergeA :: (Applicative f, Ord k) => WhenMissing f k a c -> WhenMissing f k b c -> WhenMatched f k a b c -> Map k a -> Map k b -> f (Map k c)
- zipWithMaybeAMatched :: Applicative f => (k -> x -> y -> f (Maybe z)) -> WhenMatched f k x y z
- zipWithAMatched :: Applicative f => (k -> x -> y -> f z) -> WhenMatched f k x y z
- traverseMaybeMissing :: Applicative f => (k -> x -> f (Maybe y)) -> WhenMissing f k x y
- traverseMissing :: Applicative f => (k -> x -> f y) -> WhenMissing f k x y
- filterAMissing :: Applicative f => (k -> x -> f Bool) -> WhenMissing f k x x
- mapWhenMissing :: Functor f => (a -> b) -> WhenMissing f k x a -> WhenMissing f k x b
- mapWhenMatched :: Functor f => (a -> b) -> WhenMatched f k x y a -> WhenMatched f k x y b
- runWhenMatched :: WhenMatched f k x y z -> k -> x -> y -> f (Maybe z)
- runWhenMissing :: WhenMissing f k x y -> k -> x -> f (Maybe y)
Simple merge tactic types
type SimpleWhenMissing = WhenMissing Identity Source #
A tactic for dealing with keys present in one map but not the other in
merge
.
A tactic of type SimpleWhenMissing k x z
is an abstract representation
of a function of type k -> x -> Maybe z
.
Since: containers-0.5.9
type SimpleWhenMatched = WhenMatched Identity Source #
A tactic for dealing with keys present in both maps in merge
.
A tactic of type SimpleWhenMatched k x y z
is an abstract representation
of a function of type k -> x -> y -> Maybe z
.
Since: containers-0.5.9
General combining function
:: Ord k | |
=> SimpleWhenMissing k a c | What to do with keys in |
-> SimpleWhenMissing k b c | What to do with keys in |
-> SimpleWhenMatched k a b c | What to do with keys in both |
-> Map k a | Map |
-> Map k b | Map |
-> Map k 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 0 'a', f 1 'b' "one", g2 2 "two", g1 3 'c', f 4 'd' "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,
dropMissing
drops all the keys.preserveMissing
leaves 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 preserveMissing dropMissing (zipWithMatched f)
symmetricDifference = merge preserveMissing preserveMissing (zipWithMaybeMatched $ \ _ _ _ -> Nothing)
mapEachPiece f g h = merge (mapMissing f) (mapMissing g) (zipWithMatched h)
Since: containers-0.5.9
WhenMatched
tactics
zipWithMaybeMatched :: Applicative f => (k -> x -> y -> Maybe z) -> WhenMatched f k x y z Source #
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 :: (k -> x -> y -> Maybe z) -> SimpleWhenMatched k x y z
zipWithMatched :: Applicative f => (k -> x -> y -> z) -> WhenMatched f k x y z Source #
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 :: (k -> x -> y -> z) -> SimpleWhenMatched k x y z
WhenMissing
tactics
mapMaybeMissing :: Applicative f => (k -> x -> Maybe y) -> WhenMissing f k x y Source #
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 :: (k -> x -> Maybe y) -> SimpleWhenMissing k x y
mapMaybeMissing f = traverseMaybeMissing (\k x -> pure (f k x))
but mapMaybeMissing
uses fewer unnecessary Applicative
operations.
dropMissing :: Applicative f => WhenMissing f k x y Source #
Drop all the entries whose keys are missing from the other map.
dropMissing :: SimpleWhenMissing k x y
dropMissing = mapMaybeMissing (\_ _ -> Nothing)
but dropMissing
is much faster.
Since: containers-0.5.9
preserveMissing :: Applicative f => WhenMissing f k x x Source #
Preserve, unchanged, the entries whose keys are missing from the other map.
preserveMissing :: SimpleWhenMissing k x x
preserveMissing = Merge.Lazy.mapMaybeMissing (\_ x -> Just x)
but preserveMissing
is much faster.
Since: containers-0.5.9
preserveMissing' :: Applicative f => WhenMissing f k x x Source #
Force the entries whose keys are missing from the other map and otherwise preserve them unchanged.
preserveMissing' :: SimpleWhenMissing k x x
preserveMissing' = Merge.Lazy.mapMaybeMissing (\_ x -> Just $! x)
but preserveMissing'
is quite a bit faster.
Since: containers-0.5.9
mapMissing :: Applicative f => (k -> x -> y) -> WhenMissing f k x y Source #
Map over the entries whose keys are missing from the other map.
mapMissing :: (k -> x -> y) -> SimpleWhenMissing k x y
mapMissing f = mapMaybeMissing (\k x -> Just $ f k x)
but mapMissing
is somewhat faster.
filterMissing :: Applicative f => (k -> x -> Bool) -> WhenMissing f k x x Source #
Filter the entries whose keys are missing from the other map.
filterMissing :: (k -> x -> Bool) -> SimpleWhenMissing k 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 k x y Source #
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 k -> x -> f (Maybe z)
.
Since: containers-0.5.9
Instances
(Applicative f, Monad f) => Category (WhenMissing f k :: Type -> Type -> Type) # | Since: containers-0.5.9 |
Defined in Data.Map.Internal id :: forall (a :: k0). WhenMissing f k a a Source # (.) :: forall (b :: k0) (c :: k0) (a :: k0). WhenMissing f k b c -> WhenMissing f k a b -> WhenMissing f k a c Source # | |
(Applicative f, Monad f) => Monad (WhenMissing f k x) # | Equivalent to Since: containers-0.5.9 |
Defined in Data.Map.Internal (>>=) :: WhenMissing f k x a -> (a -> WhenMissing f k x b) -> WhenMissing f k x b Source # (>>) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x b Source # return :: a -> WhenMissing f k x a Source # | |
(Applicative f, Monad f) => Functor (WhenMissing f k x) # | Since: containers-0.5.9 |
Defined in Data.Map.Internal fmap :: (a -> b) -> WhenMissing f k x a -> WhenMissing f k x b Source # (<$) :: a -> WhenMissing f k x b -> WhenMissing f k x a Source # | |
(Applicative f, Monad f) => Applicative (WhenMissing f k x) # | Equivalent to Since: containers-0.5.9 |
Defined in Data.Map.Internal pure :: a -> WhenMissing f k x a Source # (<*>) :: WhenMissing f k x (a -> b) -> WhenMissing f k x a -> WhenMissing f k x b Source # liftA2 :: (a -> b -> c) -> WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x c Source # (*>) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x b Source # (<*) :: WhenMissing f k x a -> WhenMissing f k x b -> WhenMissing f k x a Source # |
data WhenMatched f k x y z Source #
A tactic for dealing with keys present in both
maps in merge
or mergeA
.
A tactic of type WhenMatched f k x y z
is an abstract representation
of a function of type k -> x -> y -> f (Maybe z)
.
Since: containers-0.5.9
Instances
(Monad f, Applicative f) => Category (WhenMatched f k x :: Type -> Type -> Type) # | Since: containers-0.5.9 |
Defined in Data.Map.Internal id :: forall (a :: k0). WhenMatched f k x a a Source # (.) :: forall (b :: k0) (c :: k0) (a :: k0). WhenMatched f k x b c -> WhenMatched f k x a b -> WhenMatched f k x a c Source # | |
(Monad f, Applicative f) => Monad (WhenMatched f k x y) # | Equivalent to Since: containers-0.5.9 |
Defined in Data.Map.Internal (>>=) :: WhenMatched f k x y a -> (a -> WhenMatched f k x y b) -> WhenMatched f k x y b Source # (>>) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y b Source # return :: a -> WhenMatched f k x y a Source # | |
Functor f => Functor (WhenMatched f k x y) # | Since: containers-0.5.9 |
Defined in Data.Map.Internal fmap :: (a -> b) -> WhenMatched f k x y a -> WhenMatched f k x y b Source # (<$) :: a -> WhenMatched f k x y b -> WhenMatched f k x y a Source # | |
(Monad f, Applicative f) => Applicative (WhenMatched f k x y) # | Equivalent to Since: containers-0.5.9 |
Defined in Data.Map.Internal pure :: a -> WhenMatched f k x y a Source # (<*>) :: WhenMatched f k x y (a -> b) -> WhenMatched f k x y a -> WhenMatched f k x y b Source # liftA2 :: (a -> b -> c) -> WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y c Source # (*>) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y b Source # (<*) :: WhenMatched f k x y a -> WhenMatched f k x y b -> WhenMatched f k x y a Source # |
Applicative general combining function
:: (Applicative f, Ord k) | |
=> WhenMissing f k a c | What to do with keys in |
-> WhenMissing f k b c | What to do with keys in |
-> WhenMatched f k a b c | What to do with keys in both |
-> Map k a | Map |
-> Map k b | Map |
-> f (Map k 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 0 'a', f 1 'b' "one", g2 2 "two", g1 3 'c', f 4 'd' "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,
dropMissing
drops all the keys.preserveMissing
leaves all the entries alone.mapMaybeMissing
does not use theApplicative
context.
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 :: Applicative f => (k -> x -> y -> f (Maybe z)) -> WhenMatched f k x y z Source #
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.
zipWithAMatched :: Applicative f => (k -> x -> y -> f z) -> WhenMatched f k x y z Source #
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.
WhenMissing
tactics
traverseMaybeMissing :: Applicative f => (k -> x -> f (Maybe y)) -> WhenMissing f k x y Source #
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.
traverseMissing :: Applicative f => (k -> x -> f y) -> WhenMissing f k x y Source #
Traverse over the entries whose keys are missing from the other map.
filterAMissing :: Applicative f => (k -> x -> f Bool) -> WhenMissing f k x x Source #
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 :: Functor f => (a -> b) -> WhenMissing f k x a -> WhenMissing f k x b Source #
Map covariantly over a
.WhenMissing
f k x
mapWhenMatched :: Functor f => (a -> b) -> WhenMatched f k x y a -> WhenMatched f k x y b Source #
Map covariantly over a
.WhenMatched
f k x y
Miscellaneous functions on tactics
runWhenMatched :: WhenMatched f k x y z -> k -> x -> y -> f (Maybe z) Source #
Along with zipWithMaybeAMatched, witnesses the isomorphism between
WhenMatched f k x y z
and k -> x -> y -> f (Maybe z)
.
Since: containers-0.5.9
runWhenMissing :: WhenMissing f k x y -> k -> x -> f (Maybe y) Source #
Along with traverseMaybeMissing, witnesses the isomorphism between
WhenMissing f k x y
and k -> x -> f (Maybe y)
.
Since: containers-0.5.9