Struct ScopeSnapshot 

pub struct ScopeSnapshot { /* private fields */ }

A snapshot of the staging-related fields of EvalCtx. Used to save and restore the staging context at scope boundaries (reify, reifyc, reifyv, run_now, Catch).

Replaces the closure-passed run_scope pattern of the recursive baseline with a value we can name, hold on a continuation, and inspect in tests. The discipline is identical: every save must be paired with exactly one restore.

level is not part of ScopeSnapshot because it’s saved independently in RunNowExit — level only changes at run-now boundaries, not at every reify scope.

Implementations

impl ScopeSnapshot

pub fn save(ctx: &mut EvalCtx) -> Self

Save the current staging state. The saved block is taken via mem::take — callers who want to start fresh in the new scope will set ctx.block = Vec::new() afterwards (typically via save_and_reset_block for ergonomics).

fun is Rc::cloned (O(1) refcount bump, not a structural copy).

pub fn save_and_reset_block(ctx: &mut EvalCtx) -> Self

Save and reset block to empty. Equivalent to:

let snap = ScopeSnapshot::save(ctx);
// ctx.block is already Vec::new() because mem::take left it empty.

Provided for symmetry with save — most reify-style scopes want the block reset, so this is the common path. Functionally equivalent to plain save but more explicit at the call site.

pub fn restore(self, ctx: &mut EvalCtx)

Restore the saved state into ctx. Consumes the snapshot — each snapshot may be restored at most once.