Alpha. Vary is under active development and not ready for production use. Syntax, APIs, performance, and behaviour may change between releases.

Collections

The collections module provides generic higher-order functions for working with lists, dicts, and sets. Import individual functions rather than the whole module:

from collections import first, filter, group_by

let nums = [3, 1, 4, 1, 5, 9, 2, 6]

let evens = filter(nums, lambda n: Int: n % 2 == 0)
let first_even = first(evens)

let words = ["apple", "avocado", "banana", "blueberry", "cherry"]
let by_letter = group_by(words, lambda w: Str: w[0])
# {"a": ["apple", "avocado"], "b": ["banana", "blueberry"], "c": ["cherry"]}

Note: These are free functions imported from the collections module, not methods on collection types. Built-in instance methods (.append(), .keys(), .add(), etc.) are documented separately.

List utilities

Function	Returns	Description
`first(items)`	`T`	First element; raises if empty
`last(items)`	`T`	Last element; raises if empty
`is_empty(items)`	`Bool`	True if the list has no elements
`index_of(items, value)`	`Int`	Index of first occurrence, or `-1` if not found
`map(items, fn)`	`List[U]`	Apply `fn` to every element, collect results
`filter(items, fn)`	`List[T]`	Keep elements where `fn` returns `True`
`flat_map(items, fn)`	`List[U]`	Map then flatten one level
`reduce(items, init, fn)`	`U`	Fold list into a single value starting from `init`
`any(items, fn)`	`Bool`	True if `fn` returns `True` for at least one element
`all(items, fn)`	`Bool`	True if `fn` returns `True` for every element
`find(items, fn)`	`T?`	First element where `fn` is `True`, or `None`
`unique(items)`	`List[T]`	Remove duplicates, preserving first occurrence order
`chunk(items, size)`	`List[List[T]]`	Split into sub-lists of at most `size` elements
`flatten(items)`	`List[T]`	Flatten one level of nesting
`sorted(items)`	`List[T]`	Return a new sorted list (natural order)
`sorted_by(items, key)`	`List[T]`	Return a new list sorted by the result of `key`
`group_by(items, key)`	`Dict[K, List[T]]`	Partition elements by the result of `key`

from collections import map, filter, reduce, sorted_by, find, chunk

let scores = [72, 95, 88, 41, 63, 99]

let passing = filter(scores, lambda s: Int: s >= 70)
# [72, 95, 88, 63, 99]

let doubled = map(passing, lambda s: Int: s * 2)
# [144, 190, 176, 126, 198]

let total = reduce(scores, 0, lambda acc: Int, s: Int: acc + s)
# 458

let ranked = sorted_by(scores, lambda s: Int: -s)
# [99, 95, 88, 72, 63, 41]

let first_failing = find(scores, lambda s: Int: s < 70)
# 41

let pages = chunk(scores, 2)
# [[72, 95], [88, 41], [63, 99]]

Dict utilities

Function	Returns	Description
`keys(d)`	`List[K]`	All keys as a list
`values(d)`	`List[V]`	All values as a list
`items(d)`	`List[(K, V)]`	All key-value pairs as a list of tuples
`invert(d)`	`Dict[V, K]`	Swap keys and values
`merge(left, right)`	`Dict[K, V]`	Combine two dicts; `right` wins on conflicts
`get_or(d, key, default)`	`V`	Look up `key`, returning `default` if absent

from collections import keys, values, items, invert, merge, get_or

let config = {"host": "localhost", "port": "8080", "env": "dev"}

let all_keys = keys(config)
# ["host", "port", "env"]

let overrides = {"port": "9090", "debug": "true"}
let merged = merge(config, overrides)
# {"host": "localhost", "port": "9090", "env": "dev", "debug": "true"}

let port = get_or(merged, "timeout", "30")
# "30"

let codes = {"ok": 200, "not_found": 404}
let by_code = invert(codes)
# {200: "ok", 404: "not_found"}

Set utilities

Function	Returns	Description
`union(a, b)`	`Set[T]`	All elements in either set
`intersection(a, b)`	`Set[T]`	Only elements present in both sets
`difference(a, b)`	`Set[T]`	Elements in `a` but not in `b`
`is_subset(a, b)`	`Bool`	True if every element of `a` is also in `b`

from collections import union, intersection, difference, is_subset

let backend = {"alice", "bob", "carol"}
let frontend = {"bob", "carol", "dave"}

let team = union(backend, frontend)
# {"alice", "bob", "carol", "dave"}

let fullstack = intersection(backend, frontend)
# {"bob", "carol"}

let backend_only = difference(backend, frontend)
# {"alice"}

print(is_subset(fullstack, backend))
# True

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