feat: add Extras.Queue, an immutable FIFO queue - #1
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Add `Extras.Queue`: a persistent first-in, first-out queue. The standard library provides `MutDeque` and `MutPriorityQueue`, but no immutable queue. The queue is represented as a pair of lists -- a front list in queue order and a back list in reverse queue order -- maintaining the invariant that the front is empty only if the queue is empty. This gives `enqueue`, `dequeue`, and `peek` amortized constant time. The interface is deliberately minimal: `empty`, `isEmpty`, `size`, `enqueue`, `dequeue`, `peek`, `toList`, and `fromList`, plus `Eq` and `ToString` instances. `Eq` compares queue order rather than representation, since the same elements can be split differently across the front and back lists. Includes 30 tests, three per operation. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01V83KMjbi6D8deDr3zyiinK
magnus-madsen
changed the title
The `Queue` enum is declared in the body of `mod Extras.Queue`, so it is already in scope both as a type and for its case constructor. The `use` was redundant. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01V83KMjbi6D8deDr3zyiinK
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Adds
Extras.Queue, a persistent first-in, first-out queue — the first module in this library.Why a queue
The standard library has
MutDequeandMutPriorityQueue, and persistentChain,Nec, andNel, but no immutable queue. This fills that gap.Representation
A pair of lists: a front list in queue order, and a back list in reverse queue order. Elements are dequeued from the front and enqueued onto the back; when the front is exhausted the back is reversed to become the new front. This gives
enqueue,dequeue, andpeekamortized constant time.The private
unitsmart constructor maintains the invariant that the front list is empty only if the queue is empty, which letsisEmptyandpeekbe constant-time reads of the front.