Struct Env 

pub struct Env { /* private fields */ }

An evaluation environment mapping variable names to values.

Environments are immutable, and extending one shares it rather than copying it: the extension holds a reference to the scope it extends, so binding a name costs the same whatever else is in scope. That matters because the evaluator extends the environment on every let, every lambda, and every closure application.

A name bound twice is shadowed by the inner binding, and only the inner one is observable: get returns it, iter yields it, and len counts the name once.

Implementations

impl Env

pub const fn new() -> Self

Create an empty environment.

pub fn get(&self, name: &str) -> Option<&Literal>

Look up a variable in the environment.

pub fn extend(&self, name: Arc<str>, value: Literal) -> Self

Extend the environment with a new binding, returning a new environment.

The environment extended is left as it was, and is shared rather than copied, so this costs the same at any width.

pub fn len(&self) -> usize

Returns the number of distinct names in scope.

pub const fn is_empty(&self) -> bool

Returns true if the environment has no bindings.

pub fn iter(&self) -> impl Iterator<Item = (&Arc<str>, &Literal)>

Iterate over the bindings in scope, in name order, each name once.

Name order rather than the order the bindings arrived in, so that two environments holding the same bindings read the same however they were assembled — which is what lets a hash or an encoding taken over an environment be a function of what it binds.

Trait Implementations

impl Clone for Env

fn clone(&self) -> Env

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Env

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

Formats the value using the given formatter.

impl Default for Env

fn default() -> Env

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for Env

fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error>

Deserialize this value from the given Serde deserializer.

impl Eq for Env

impl FromIterator<(Arc<str>, Literal)> for Env

fn from_iter<T: IntoIterator<Item = (Arc<str>, Literal)>>(iter: T) -> Self

Build an environment from bindings, later ones shadowing earlier ones.

impl Hash for Env

fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Env

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl Serialize for Env

fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error>

Serialize this value into the given Serde serializer.