Reliev 🩹

Undo/redo for observ-based reactive state.

📖 Documentation | Quick Start | API Reference

Reliev is a complementary store library for observ. Subclass Store, mark state-changing methods with @mutation, and every call records a single undo/redo history entry. Patchdiff records the changes as bidirectional patches, so a mutation costs what it changes — not the size of your state — and undo/redo trigger exactly the fine-grained reactive notifications the original change did.

from reliev import Store, computed, mutation

class TodoStore(Store):
    @mutation(context=lambda self, item: f"Add {item}")
    def add_item(self, item):
        self.state["items"].append(item)

    @computed
    def item_count(self):
        return len(self.state["items"])

store = TodoStore({"items": []})
store.add_item("apple")

assert store.item_count == 1
assert store.undo_context == "Add apple"  # e.g. menu item "Undo Add apple"

store.undo()
assert store.item_count == 0

store.redo()
assert store.item_count == 1

Features

• Transactional mutations — one mutation call is one undo step; nested mutation calls collapse into the outermost entry
• Mutation context — attach any (hashable) value or a callable to a mutation for user-facing undo/redo labels, and read it back through the reactive undo_context/redo_context properties
• Computed properties — expose derived state as cached, reactive, read-only store properties
• Strict mode — mutations that change nothing raise by default; opt out per store or per mutation
• Fully reactive — state, history flags and contexts all compose with observ's watch and computed
• Typed — complete type hints, PEP 561 py.typed, checked with ty in CI