Type Alias WeakEnv 

pub type WeakEnv<'a> = Weak<Environment<'a>>;

A non-owning reference to an environment. Used by function closures so that the env->function->closure->env cycle does not leak: the interpreter’s env arena keeps every environment alive for the eval’s duration instead (D9).

Aliased Type

pub struct WeakEnv<'a> { /* private fields */ }