Immutables 1.2.0

Deprecated

peek_overlaps(), peek_all_overlaps(), pop_overlaps(), and pop_all_overlaps() are renamed to peek_overlapping(), peek_all_overlapping(), pop_overlapping(), and pop_all_overlapping(). The new names match peek_containing() and make clear that the non-all versions return a single match. The old names still work but emit a deprecation warning, and will be removed in a future release.

pop_front(), pop_back(), and pop_at() on an ordered_sequence now return the popped element’s key alongside value and remaining (NULL on a miss), matching pop_key(), pop_min(), and the interval pop_* helpers. Plain flexseq pops are unchanged.
New key_at() reads the key of an ordered_sequence element at a given one-based position without removing it (the positional companion to peek_at(), and the general form of min_key() / max_key()).
New nearest_key() returns the existing key closest to a query key, composing with peek_key() / pop_key(). It resolves by order alone at the extremes and on an exact hit (any key type), and uses abs(query - key) when the query falls strictly between two distinct keys (numeric/Date/POSIXct). The ties argument resolves an equidistant tie between two distinct keys: "lower" (default), "upper", or "both" (returns both keys). It errors for non-subtractable keys (e.g. character) in that between case, where “closer” is undefined.

ordered_sequence key-boundary lookups now use a native C++ descent for numeric, character, and logical keys, speeding up lower_bound(), upper_bound(), peek_key(), pop_key(), peek_all_key(), pop_all_key(), count_key(), elements_between(), and count_between().
The implementation now uses lazy evaluation matching the Hinze and Paterson reference implementation, making amortized-constant-time end access claims true when structures are used in a persistent setting.

interval_index queries and removals now run through a native C++ engine, yielding large speedups.
Interval endpoints now use the same native query fast path as other structures for character, Date, or POSIXct (in addition to numeric and integer) endpoints.

Corrected the documented return field of the interval pop_* functions to $value
Clarified that peek_point() and the other “first match” interval queries return the match in canonical interval order: smallest start, with insertion/FIFO order breaking ties.
Hardened the pure-R reference tree builder against C-stack overflow when constructing very large structures, by replacing a deep recursion in the bulk builder with iterative node grouping.
Reworking benchmarks vignette in preparation for publication.

CRAN resubmission. Addresses reviewer feedback:
- Added a reference to Hinze and Paterson (2006) doi:10.1017/S0956796805005769 in DESCRIPTION.
- Added missing \value tag for print.flexseq().
- Removed \dontrun{} example wrappers from internal helpers.
Removed the plot() in favor of plot_structure() as part of the developer API.
Added inst/CITATION with a Zenodo DOI for the package.

First CRAN submission.
flexseqs: list-like sequences with push/pop/peek from either end, indexed and named access, insertion, splitting, and concatenation.
priority_queues, ordered_sequences, interval_indexes: finger-tree-backed structures for min/max-by-priority, sorted-by-key, and interval-overlap queries.
Developer API for building custom structures via monoid/measure combinations.
Core operations implemented in C++ via Rcpp, with matching pure-R reference implementations using lambda.r.