Sets and Maps

Flix has excellent support for (immutable) Sets and Map based on balanced trees; hence the elements of a Set and the keys of Map must implement the Order type class.

Tip: The Flix Set and Map data structures will automatically parallelize certain operations. Such operations are marked with @ParallelWhenPure in the API docs.


The empty set is written as:


which is equivalent to Set.empty(). A set literal is written as:

Set#{1, 2, 3}

We can insert into a set using Set.insert (which returns a new set):

let s1 = Set#{1, 2, 3};
let s2 = Set.insert(4, s1);

We can determine if a set contains an element using Set.memberOf:

let s = Set#{1, 2, 3};
Set.memberOf(2, s)

We can merge two sets using Set.union:

let s1 = Set#{1, 2, 3};
let s2 = Set#{3, 4, 5};
let sr = Set.union(s1, s2);

Since Sets are SemiGroups, we can also use the ++ operator and write s1 ++ s2.


The empty map is written as:


which is equivalent to Map.empty(). A map literal is written as:

Map#{"a" => 1, "b" => 2, "c" => 3}

We can insert into a map using Map.insert (which returns a new map):

let m1 = Map#{"a" => 1, "b" => 2, "c" => 3};
let m2 = Map.insert("d", 4, m1);

We can lookup the value associated with a key using Map.get:

let m = Map#{"a" => 1, "b" => 2, "c" => 3};
Map.get("b", m) 

The Map.get function returns an Option[v].

We can merge two maps using one of Map.unionWith and Map.unionWithKey functions.