Struct Environment 

pub struct Environment {
    pub enclosing: Option<Rc<RefCell<Environment>>>,
    /* private fields */
}

Represents an environment in which variables are stored. The environment is a hash map of variable names to their values. Each environment has a reference to its enclosing environment. This is an optional reference to implement lexical scoping and closures.

Fields

enclosing: Option<Rc<RefCell<Environment>>>

Using an Rc and Refcell here allows us to have multiple mutable references to the same environment.

Implementations

impl Environment

pub fn new(enclosing: Option<Rc<RefCell<Environment>>>) -> Self

Creates a new environment with the given enclosing environment.

pub fn define(&mut self, name: &str, value: Object)

Defines a new variable in the environment with the given name and value.

pub fn assign(&mut self, name: &Token, value: Object)

Assigns the given value to the variable with the given name. If the variable is not define in this environment but is defined in an enclosing environment, it will try to recursively assign the value to the variable in the enclosing environment. If the variable is not defined in this environment or any enclosing environment, it will throw a runtime error.

pub fn assign_at(&mut self, distance: usize, name: &Token, value: Object)

Works like Environment::assign but assigns the value to the variable in the ancestor environment at the given distance.

pub fn get(&self, name: &Token) -> Result<Object, RuntimeError>

Returns the value of the variable with the given name. If the variable is not defined in this environment but is defined in an enclosing environment, it will try to recursively get the value of the variable in the enclosing environment. If the variable is not defined in this environment or any enclosing environment, it will throw a runtime error.

pub fn get_at( &self, distance: usize, name: &Token, ) -> Result<Object, RuntimeError>

Works like Environment::get but gets the value of the variable in the ancestor environment at the given distance.

Trait Implementations

impl Clone for Environment

fn clone(&self) -> Environment

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Environment

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Environment

fn default() -> Self

Returns the “default value” for a type.