set

The set module provides an unordered collection of unique elements, backed by HashMap for O(1) lookup.

Import

from std::core::set use {
  new, from_array, add, remove, includes, union,
  intersection, difference, to_array, len
}

Creating Sets

let empty = new()
let s = from_array(["a", "b", "c", "b", "a"])   // deduplicates → {"a","b","c"}

Note: at HEAD 0c56ab86, the underlying HashMap rejects non-string keys. Until W17.3-4.3-adjacent HashMap-key-kind work lands, sets of int or other non-string elements will surface HashMap key must be a string (got kind ...) at runtime.

Operations

let s = from_array(["a", "b", "c"])

let s2 = add(s, "d")
let s3 = remove(s2, "b")

print(includes(s3, "a"))   // true
print(includes(s3, "b"))   // false
print(len(s3))             // 3
print(to_array(s3))        // ["a", "c", "d"]

Set Algebra

let a = from_array(["x", "y", "z"])
let b = from_array(["y", "z", "w"])

let u = union(a, b)          // {"x","y","z","w"}
let i = intersection(a, b)   // {"y","z"}
let d = difference(a, b)     // {"x"}

Functions

Function	Description
`new()`	Create an empty set
`from_array(arr)`	Create a set from an array (deduplicates)
`add(s, item)`	Return new set with item added
`remove(s, item)`	Return new set with item removed
`includes(s, item)`	Check if set contains item
`union(a, b)`	Union of two sets
`intersection(a, b)`	Intersection of two sets
`difference(a, b)`	Difference (a minus b)
`to_array(s)`	Convert set to array
`len(s)`	Number of elements

Sets are immutable — add, remove, and set algebra functions return new sets.