[feat] Add Stateful trait (#20)

* Add Stateful trait

* Update Cargo.toml

---------

Co-authored-by: Jonathan Wang <[email protected]>

Author: nyunyunyunyu

crates/stark-backend/src/chip.rs

@@ -37,6 +37,12 @@ pub trait ChipUsageGetter {
     }
 }
 
+/// A chip whose state could be persisted.
+pub trait Stateful<S> {
+    fn load_state(&mut self, state: S);
+    fn store_state(&self) -> S;
+}
+
 impl<SC: StarkGenericConfig, C: Chip<SC>> Chip<SC> for RefCell<C> {
     fn air(&self) -> Arc<dyn AnyRap<SC>> {
         self.borrow().air()
@@ -140,3 +146,12 @@ impl<C: ChipUsageGetter> ChipUsageGetter for Mutex<C> {
         self.lock().unwrap().trace_width()
     }
 }
+
+impl<S, C: Stateful<S>> Stateful<S> for RefCell<C> {
+    fn load_state(&mut self, state: S) {
+        self.borrow_mut().load_state(state)
+    }
+    fn store_state(&self) -> S {
+        self.borrow_mut().store_state()
+    }
+}

crates/stark-backend/src/lib.rs

@@ -41,7 +41,7 @@ pub mod utils;
 /// Verifier implementation
 pub mod verifier;
 
-pub use chip::{Chip, ChipUsageGetter};
+pub use chip::{Chip, ChipUsageGetter, Stateful};
 
 // Use jemalloc as global allocator for performance
 #[cfg(all(feature = "jemalloc", unix, not(test)))]