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Changelog

All notable changes to Mnemosyne are documented in this file.

The project follows Semantic Versioning (MAJOR.MINOR.PATCH). While in the 0.x series, APIs may evolve as the architecture matures.

[0.7.0] - 2026-03-29

Added

New Data Structures

TimeAwareHeap (priority queue with history)

  • Immutable min-heap with version IDs, checkpoints, undo/redo, and diffing
  • Operations:
    • push — Insert element at a version (O(log n))
    • pop — Remove smallest element, returns (value, new_version_id)
    • peek — View smallest element
    • checkpoint / jump_to_checkpoint — Named savepoints
    • undo / redo — Navigate version history
    • diff — Added/removed elements between versions

Examples

  • examples/example_timeaware_heap.py — Versioned heap usage with checkpoints

Test Coverage

  • 9 new tests covering versioning, checkpoints, undo/redo, diffs, and errors
  • Total test suite: 126 comprehensive tests

Changed

  • Version updated: 0.6.0 → 0.7.0
  • __init__.py exports expanded to include TimeAwareHeap

[0.6.0] - 2026-03-29

Added

New Data Structures

PersistentHeap (priority queue)

  • Immutable min-heap with tuple-backed storage and structural sharing
  • Operations:
    • push — Insert element (O(log n))
    • pop — Remove smallest element, returns (value, new_heap)
    • peek — View smallest element
    • from_iterable — Build heap from any iterable
  • Maintains immutability and leaves prior heaps untouched

Examples

  • examples/example_heap.py — Demonstrates push, pop, peek, and structural sharing

Test Coverage

  • 9 new tests covering heap creation, ordering, pop sequencing, and immutability
  • Total test suite: 117 comprehensive tests

Changed

  • Version updated: 0.5.0 → 0.6.0
  • __init__.py exports expanded to include PersistentHeap

[0.5.0] - 2026-03-13

Added

New Data Structures

PersistentDoublyLinkedList

  • Bidirectional linked list enabling efficient front/back operations
  • Operations:
    • append — Add element at end (O(1))
    • prepend — Add element at start (O(1))
    • pop_front — Remove from start (O(1))
    • pop_back — Remove from end (O(1))
    • peek_front / peek_back — View without removing
    • reverse — Create reversed copy (O(n))
  • Full version preservation and structural sharing

PersistentSet

  • Hash-based immutable set with set algebra
  • Operations:
    • add, remove, contains — Core membership
    • union — Combine both sets
    • intersection — Common elements only
    • difference — Elements in first set only
  • 16-bucket hash table with collision chaining via linked lists
  • Full version preservation

PersistentCounter

  • Immutable frequency counter (multiset)
  • Operations:
    • increment(item, amount) — Increase frequency
    • decrement(item, amount) — Decrease frequency (validates count >= amount)
    • get_count(item) — Query frequency
    • total() — Sum of all counts
    • most_common(n) / least_common(n) — Frequency analysis
    • add(other) / subtract(other) — Arithmetic with operators
  • Full version preservation
  • Input validation on all operations

Examples

  • examples/example_doublylinkedlist.py — Bidirectional list operations
  • examples/example_set.py — Set algebra and membership testing
  • examples/example_counter.py — Frequency counting and analysis

Test Coverage

  • 42 new tests across 3 test classes
  • Total test suite: 108 comprehensive tests
  • 100% pass rate

Changed

  • Version updated: 0.4.0 → 0.5.0
  • __init__.py exports expanded from 7 to 10 data structures

[0.4.0] - 2026-02-13

Added

PersistentDeque

  • Fully persistent double-ended queue

  • Implemented using two persistent stacks (front/back model)

  • Structural sharing across all versions

  • Operations:

    • push_front
    • push_back
    • pop_front
    • pop_back

  • All operations return new version IDs

  • Complete historical version preservation

Version Diffing

  • diff(v1, v2) for PersistentDeque

  • Structured semantic diff output

    • Added elements
    • Removed elements

  • Enables debugging, auditing, and state inspection

  • Foundation for future structural and positional diffing

Examples

  • examples/example_deque_diff.py demonstrating:

    • Version creation
    • State transitions
    • Cross-version comparison

[0.3.0] - 2026-01-30

Added

PersistentDeque (Initial Release)

  • Double-ended immutable structure
  • Built from two persistent stacks
  • Amortized efficient operations
  • Version-aware design compatible with Mnemosyne philosophy

Documentation

  • Modernized README formatting
  • Emoji-based section headers
  • Design Overview section
  • Project Status and roadmap
  • Clear emphasis on structural sharing

[0.2.0] - 2026-01-27

Added

PersistentStack

  • Immutable stack with structural sharing

  • Operations:

    • push
    • pop
    • peek
    • is_empty

  • All operations return new stack instances

PersistentQueue

  • Immutable queue via two-stack implementation

  • Amortized O(1) enqueue/dequeue

  • Automatic rebalancing

  • Operations:

    • enqueue
    • dequeue
    • peek
    • is_empty

Examples

  • examples/example_queue.py

Changed

  • Refactored stack.py:

    • Coexistence of PersistentStack and TimeAwareStack

  • Improved internal structural sharing

  • Cleaner separation of responsibilities between stack variants

[0.1.0] - 2026-01-26

Initial Release

TimeAwareStack

  • Versioned immutable stack

  • Time-travel capabilities:

    • push
    • pop
    • peek

  • Historical inspection via show_version

  • Named checkpoints:

    • checkpoint
    • jump_to_checkpoint

  • Undo/redo support

  • Version comparison utilities

  • Stack visualization

Core Architecture

  • Immutable Node class (linked-list backbone)
  • Structural sharing foundation
  • MIT License
  • Comprehensive README
  • examples/example.py demonstrating time-aware operations

Philosophy

  • Correctness over performance
  • Clarity over abstraction
  • Explicit versioning as a first-class concept

[Unreleased]

Planned

Architecture

  • Shared base abstractions for persistent structures
  • Unified version graph model
  • Branching timelines for TimeAwareStack

Data Structures

  • Persistent Binary Search Tree
  • Persistent AVL Tree
  • Persistent graph structures

Tooling

  • Positional and structural diffing
  • Enhanced version graph visualization
  • Expanded test coverage
  • Benchmarks
  • API refinement based on real usage