DA.Map
DA.Map
Note: This is only supported in Daml-LF 1.11 or later.
This module exports the generic map type Map k v and associated
functions. This module should be imported qualified, for example:
import DA.Map (Map)
import DA.Map qualified as M
This will give access to the Map type, and the various operations
as M.lookup, M.insert, M.fromList, etc.
Map k v internally uses the built-in order for the type k.
This means that keys that contain functions are not comparable
and will result in runtime errors. To prevent this, the Ord k
instance is required for most map operations. It is recommended to
only use Map k v for key types that have an Ord k instance
that is derived automatically using deriving:
data K = ...
deriving (Eq, Ord)
This includes all built-in types that aren’t function types, such as
Int, Text, Bool, (a, b) assuming a and b have default
Ord instances, Optional t and [t] assuming t has a
default Ord instance, Map k v assuming k and v have
default Ord instances, and Set k assuming k has a
default Ord instance.
Functions
fromList: Ord k => [(k, v)] -> Map k v
Create a map from a list of key/value pairs.
fromListWithL: Ord k => (v -> v -> v) -> [(k, v)] -> Map k v
Create a map from a list of key/value pairs with a combining function. The combining function is only used when a key appears multiple times in the list and it takes two arguments: the first one is the new value being inserted at that key and the second one is the value accumulated so far at that key. Examples:
>>> fromListWithL (++) [("A", [1]), ("A", [2]), ("B", [2]), ("B", [1]), ("A", [3])]
fromList [("A", [3, 2, 1]), ("B", [1, 2])]
>>> fromListWithL (++) [] == (empty : Map Text [Int])
True
: Ord k => (v -> v -> v) -> [(k, v)] -> Map k v
Create a map from a list of key/value pairs like fromListWithL
with the combining function flipped. Examples:
>>> fromListWithR (++) [("A", [1]), ("A", [2]), ("B", [2]), ("B", [1]), ("A", [3])]
fromList [("A", [1, 2, 3]), ("B", [2, 1])]
>>> fromListWithR (++) [] == (empty : Map Text [Int])
True
: Ord k => (v -> v -> v) -> [(k, v)] -> Map k v
Warning
DEPRECATED:
: Map k v -> [k]
Get the list of keys in the map. Keys are sorted according to the
built-in order for the type k, which matches the Ord k instance
when using deriving Ord.
>>> keys (fromList [("A", 1), ("C", 3), ("B", 2)])
["A", "B", "C"]
: Map k v -> [v]
Get the list of values in the map. These will be in the same order as
their respective keys from M.keys.
>>> values (fromList [("A", 1), ("B", 2)])
[1, 2]
: Map k v -> [(k, v)]
Convert the map to a list of key/value pairs. These will be ordered
by key, as in M.keys.
: Map k v
The empty map.
sizeNumber of elements in the map.
nullIs the map empty?
lookup: Ord k => k -> Map k v -> Optional v
Lookup the value at a key in the map.
member: Ord k => k -> Map k v -> Bool
Is the key a member of the map?
filter: Ord k => (v -> Bool) -> Map k v -> Map k v
Filter the Map using a predicate: keep only the entries where the
value satisfies the predicate.
: Ord k => (k -> v -> Bool) -> Map k v -> Map k v
Filter the Map using a predicate: keep only the entries which
satisfy the predicate.
: Ord k => k -> Map k v -> Map k v
Delete a key and its value from the map. When the key is not a member of the map, the original map is returned.
singletonCreate a singleton map.
insert: Ord k => k -> v -> Map k v -> Map k v
Insert a new key/value pair in the map. If the key is already present in the map, the associated value is replaced with the supplied value.
insertWith: Ord k => (v -> v -> v) -> k -> v -> Map k v -> Map k v
Insert a new key/value pair in the map. If the key is already
present in the map, it is combined with the previous value using the given function
f new_value old_value.
: Ord k => (Optional v -> Optional v) -> k -> Map k v -> Map k v
Update the value in m at k with f, inserting or deleting as
required. f will be called with either the value at k, or None
if absent; f can return Some with a new value to be inserted in
m (replacing the old value if there was one), or None to remove
any k association m may have.
Some implications of this behavior:
alter identity k = identity alter g k . alter f k = alter (g . f) k alter (_ -> Some v) k = insert k v alter (_ -> None) = delete
union: Ord k => Map k v -> Map k v -> Map k v
The union of two maps, preferring the first map when equal keys are encountered.
unionWith: Ord k => (v -> v -> v) -> Map k v -> Map k v -> Map k v
The union of two maps using the combining function to merge values that exist in both maps.
merge: Ord k => (k -> a -> Optional c) -> (k -> b -> Optional c) -> (k -> a -> b -> Optional c) -> Map k a -> Map k b -> Map k c
Combine two maps, using separate functions based on whether a key appears only in the first map, only in the second map, or appears in both maps.
