Arrays
Arrays are collections containing an ordered list of values. East arrays are dynamically sized and can contain an arbitrary number of values. They have integer keys, starting at zero.
Array values and types
The East type for arrays with values of type T is ArrayType(T).
There are many different array types, like ArrayType(StringType) and ArrayType(DateTimeType).
The EDK accepts standard JavaScript arrays as values for ArrayType.
| East type | Example value (JavaScript) | East object notation |
|---|---|---|
ArrayType(StringType) | [] | [] |
ArrayType(StringType) | ["a", "b", "c"] | ["a", "b", "c",] |
Constructing arrays
Arrays are constructed with the NewArray expression.
The first argument to NewArray is the type of value that can be contained within the array.
Subsequent to that, you can optionally provide a list of expressions to populate values in the new array.
| East function | Description | Example usage | Result |
|---|---|---|---|
NewArray | Create a new empty array of strings | NewArray(StringType) | [] |
NewArray | Create a new array with two strings | NewArray(StringType, [Const("a"), Const("b")]) | ["a", "b",] |
Basic operations on arrays
You can query whether a key exists in an array with In (i.e. whether an index is in range), and get the number of values with Size.
You can fetch a value from an array with its integer key (or index) using Get.
Arrays use zero-based indexing, meaning the first element has key 0n, the second 1n, and so-on.
If the key might not exist, you can specify a default value.
If you do not specify a default value and they key does not exist, a runtime error will result.
You can modify arrays by inserting, updating or deleting elements. Arrays in East are immutable. The input array will not be modified; instead a new one will be returned.
| East function | Description | Example usage | Result |
|---|---|---|---|
Size | Get the number of values in an array | Size(Const(["a", "b"])) | 2 |
In | Determine if a key is in an array | In(Const(["a", "b"]), 0n) | true |
Get | Fetch an element of an array (error if key not exist) | Get(Const(["a", "b"]), 0n) | "a" |
Get | Fetch an element of an array (with default if key not exist) | Get(Const(["a", "b"]), 2n, "") | "" |
Insert | Insert an element at the start of an array | Insert(Const([1n, 2n]), "first", 0n) | [0, 1, 2,] |
Insert | Insert an element at the end of an array | Insert(Const([1n, 2n]), "last", 3n) | [1, 2, 3,] |
Update | Update an existing value in an array | Update(Const(["a", "b"]), 0n, "A") | ["A", "b",] |
Delete | Delete the first element of an array | Delete(Const(["a", "b", "c"]), "first") | ["b", "c",] |
Delete | Delete the last element of an array | Delete(Const(["a", "b", "c"]), "last") | ["a", "b",] |
Advanced array operations
You can apply array transformations with with Filter, FilterMap, ToArray and Reduce.
These are covered in detail in later sections.
Equality and ordering
Two arrays are equal if they contain the same number of values, and each value is equal and in the same order.
Ordering of arrays is defined lexically. The first values are compared, then the second, until the end is reached. If one array is the "prefix" of another, then it is lesser.
Representation
Arrays are represented in East's canonical JSON representation as JSON arrays.
They are printed similarly by Print in East's object notation with [] delimiters and comma seperated values (but include a trailing comma).
Next steps
Continue to the next tutorial to understand how to use and manipulate sets of data with East and Elara.