set.nula

// Nulang standard library — Set operations.
// Language version: 2.0.0-alpha
// Import: `import stdlib::set`
//
// Sets are represented as arrays with no duplicates.

/// An empty set.
pub fn empty() { [] }

/// Check whether a value is in the set.
pub fn contains(set, value) {
    for x in set {
        if x == value then { return true } else {}
    };
    false
}

/// Add a value to the set (no-op if already present).
/// Returns a new set; the original is unchanged.
pub fn add(set, value) {
    if contains(set, value) then set
    else { perform Array.push(set, value) }
}

/// Remove a value from the set. Returns a new set.
pub fn remove(set, value) {
    var result = [];
    for x in set {
        if x != value then { result = perform Array.push(result, x) } else {}
    };
    result
}

/// Number of elements in the set.
pub fn size(set) { perform Array.length(set) }

/// True when the set is empty.
pub fn is_empty(set) { perform Array.length(set) == 0 }

/// Union: all elements in a or b (no duplicates).
pub fn union(a, b) {
    var result = a;
    for x in b {
        if contains(result, x) then {} else { result = perform Array.push(result, x) }
    };
    result
}

/// Intersection: elements present in both a and b.
pub fn intersect(a, b) {
    var result = [];
    for x in a {
        if contains(b, x) then { result = perform Array.push(result, x) } else {}
    };
    result
}

/// Difference: elements in a that are not in b.
pub fn difference(a, b) {
    var result = [];
    for x in a {
        if contains(b, x) then {} else { result = perform Array.push(result, x) }
    };
    result
}