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 on Lists.

Maps

The data.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 data.Map construction syntax so one easy way to create a multi item map is from a List of tuples

distributedDatasets.lib.base.data.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 data.Map might look more complicated than it really is. internal.Bin and internal.Tip are just the data constructors for data.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 data.Map manipulation functions with find base.Map in the UCM.

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

Sets

You can create a Set from a list of elements with the distributed.lib.base.data.Set.fromList constructor

distributed.lib.base.data.Set.fromList [1, 2, 3, 3, 4]
⧨
internal.Set
  (internal.Bin
    4
    2
    ()
    (internal.Bin 1 1 () internal.Tip internal.Tip)
    (internal.Bin
      2
      3
      ()
      internal.Tip
      (internal.Bin 1 4 () internal.Tip internal.Tip)))

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

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