Common collection types

Lists

One of the common things you'll be doing as a Unison programmer is managing ordered collections of one type or another. One of Unison's native data structures for this is List, which we can create between square brackets.

desserts : [Text]
desserts = ["Eclair", "Peach cobbler", "Ice cream"]

Lists can only contain values of one type at a time, and are eagerly evaluated.

An empty list is simply represented [] or with List.empty.

For the curious, the documentation for List describes the underlying data structure and details many of the common operations you might perform with it.

Maps

The Map type is Unison's way of mapping unique keys to values.

You can create a map with a single object with Map.singleton 1 "a" where 1 is the key and "a" is the value associated with that key.

Currently Unison does not have special Map construction syntax so one easy way to create a multi-item map is from a List of tuples

Map.fromList [(1, "a"), (2, "b"), (3, "c")]
⧨
internal.Bin
  3
  2
  "b"
  (internal.Bin 1 1 "a" internal.Tip internal.Tip)
  (internal.Bin 1 3 "c" internal.Tip internal.Tip)

What's printed above for a Map might look more complicated than it really is. internal.Bin and internal.Tip are just the data constructors for Map. You'll likely be working with Maps through functions in the base library instead of dealing with these terms directly. Check out a few Map manipulation functions with find data.Map in the UCM.

Issue the docs Map command in the UCM to read the Map documentation itself.

Sets

You can create a Set from a list of elements with the Set.fromList constructor

Set.fromList ["🍎", "🍎", "🍊", "🍐", "🍋", "🍊"] |> Set.toList
⧨
["🍊", "🍋", "🍎", "🍐"]

Creating a Set value enables efficient functions like Set.contains and Set.union that you might be familiar with from other languages.

You can explore these types and more collection apis in the base library.