List expressions

Literal

Creates a new list of the given elements. The elements can be of any type.

[1,2,3,4]

A list value can embed other list values.

[[1,2], [3,4], [5,6]]

Get element

a[i]

Accesses an element of the list a at index i. The index starts at 1.

If the index is out of the range of the list, it returns null.

[1,2,3,4][1]
// 1

[1,2,3,4][2]
// 2

[1,2,3,4][4]
// 4

[1,2,3,4][5]
// null

[1,2,3,4][0]
// null

If the index is negative, it starts counting the elements from the end of the list. The last element of the list is at index -1.

[1,2,3,4][-1]
// 4

[1,2,3,4][-2]
// 3

[1,2,3,4][-5]
// null

be careful!

The index of a list starts at 1. In other languages, the index starts at 0.

Filter

a[c]

Filters the list a by the condition c. The result of the expression is a list that contains all elements where the condition c evaluates to true. The other elements are excluded.

While filtering, the current element is assigned to the variable item.

[1,2,3,4][item > 2]
// [3,4]

[1,2,3,4][item > 10]
// []

[1,2,3,4][even(item)]
// [2,4]

Some

some a in b satisfies c

Iterates over the list b and evaluate the condition c for each element in the list. The current element is assigned to the variable a.

It returns true if c evaluates to true for one or more elements of b. Otherwise, it returns false.

some x in [1,2,3] satisfies x > 2
// true

some x in [1,2,3] satisfies x > 5
// false

some x in [1,2,3] satisfies even(x)
// true

some x in [1,2], y in [2,3] satisfies x < y
// true

Every

Iterates over the list b and evaluate the condition c for each element in the list. The current element is assigned to the variable a.

It returns true if c evaluates to true for all elements of b. Otherwise, it returns false.

every x in [1,2,3] satisfies x >= 1
// true

every x in [1,2,3] satisfies x >= 2
// false

every x in [1,2,3] satisfies even(x)
// false

every x in [1,2], y in [2,3] satisfies x < y
// false