Dict

A dictionary mapping unique keys to values. The keys can be any comparable type. This includes Int, Float, Time, Char, String, and tuples or lists of comparable types.

Insert, remove, and query operations all take O(log n) time.

Build

empty : Dict comparable v

Create an empty dictionary.

singleton : comparable -> v -> Dict comparable v

Create a dictionary with one key-value pair.

insert : comparable -> v -> Dict comparable v -> Dict comparable v

Insert a key-value pair into a dictionary. Replaces value when there is a collision.

update :

comparable

-> (Maybe v -> Maybe v)

-> Dict comparable v

Update the value of a dictionary for a specific key with a given function.

remove : comparable -> Dict comparable v -> Dict comparable v

Remove a key-value pair from a dictionary. If the key is not found, no changes are made.

Query

member : comparable -> Dict comparable v -> Bool

Determine if a key is in a dictionary.

get : comparable -> Dict comparable v -> Maybe v

Get the value associated with a key. If the key is not found, return Nothing. This is useful when you are not sure if a key will be in the dictionary.

animals = fromList [ ("Tom", Cat), ("Jerry", Mouse) ]


get "Tom"   animals == Just Cat
get "Mouse" animals == Just Mouse
get "Spike" animals == Nothing

The (?) operator from the Maybe library makes it easy to give a default value.

Combine

union : Dict comparable v -> Dict comparable v -> Dict comparable v

Combine two dictionaries. If there is a collision, preference is given to the first dictionary.

intersect : Dict comparable v -> Dict comparable v -> Dict comparable v

Keep a key-value pair when its key appears in the second dictionary. Preference is given to values in the first dictionary.

diff : Dict comparable v -> Dict comparable v -> Dict comparable v

Keep a key-value pair when its key does not appear in the second dictionary. Preference is given to the first dictionary.

Lists

keys : Dict comparable v -> List comparable

Get all of the keys in a dictionary.

values : Dict comparable v -> List v

Get all of the values in a dictionary.

toList : Dict comparable v -> List ( comparable, v )

Convert a dictionary into an association list of key-value pairs.

fromList : List ( comparable, v ) -> Dict comparable v

Convert an association list into a dictionary.

Transform

map : (comparable -> a -> b) -> Dict comparable a -> Dict comparable b

Apply a function to all values in a dictionary.

foldl : (comparable -> v -> b -> b) -> b -> Dict comparable v -> b

Fold over the key-value pairs in a dictionary, in order from lowest key to highest key.

foldr : (comparable -> v -> b -> b) -> b -> Dict comparable v -> b

Fold over the key-value pairs in a dictionary, in order from highest key to lowest key.

filter : (comparable -> v -> Bool) -> Dict comparable v -> Dict comparable v

Keep a key-value pair when it satisfies a predicate.

partition :

(comparable -> v -> Bool)

-> Dict comparable v

-> ( Dict comparable v, Dict comparable v )

Partition a dictionary according to a predicate. The first dictionary contains all key-value pairs which satisfy the predicate, and the second contains the rest.

elm-lang/core/1.0.0