Immutable Data

The bread-and-butter of functional programming is immutable data types.

We have already seen several examples of immutable data types:

• Primitive Types
• Tuple Types
• Enumerated, Recursive, and Polymorphic Types

In addition, The Flix standard library offers several immutable data types:

• List[t] : An immutable singly-linked list of elements of type t.
• Chain[t] : An immutable chain of elements of type t with fast append.
• Vector[t] : An immutable sequence of elements of type t with fast lookup.
• Set[t] : An immutable set of elements of type t.
• Map[k, v] : An immutable map of keys of type k to values of type v.

Other immutable data types include:

• Option[t] : A type that is either None or Some(t).
• Result[e, t] : A type that is either Ok(t) or Err(e).
• Nel[t] : An immutable non-empty singly-linked list of elements of type t.
• Nec[t] : An immutable non-empty sequence of elements of type t that supports fast append.
• MultiMap[k, v] : An immutable map of keys of type k to sets of values of type v.