Enum Expr 

pub enum Expr {
    Var(VarName),
    Lam {
        param: VarName,
        body: Box<Expr>,
    },
    App {
        func: Box<Expr>,
        arg: Box<Expr>,
    },
    Let {
        name: VarName,
        value: Box<Expr>,
        body: Box<Expr>,
    },
    Fix {
        name: VarName,
        body: Box<Expr>,
    },
    Ref {
        inner: Box<Expr>,
    },
    Deref {
        inner: Box<Expr>,
    },
    Assign {
        target: Box<Expr>,
        value: Box<Expr>,
    },
    Seq {
        first: Box<Expr>,
        second: Box<Expr>,
    },
    Object {
        entries: Vec<(VarName, Expr)>,
        prototype: Option<Box<Expr>>,
    },
    Field {
        object: Box<Expr>,
        name: VarName,
    },
    Throw {
        inner: Box<Expr>,
    },
    TryCatch {
        body: Box<Expr>,
        catch_param: VarName,
        handler: Box<Expr>,
    },
}

The abstract syntax tree.

Variants

Var(VarName)

Variable reference.

Lam

Lambda abstraction.

Fields

param: VarName

Bound parameter name.

body: Box<Expr>

Function body.

App

Function application (left-associative at the surface).

Fields

func: Box<Expr>

The function being applied.

arg: Box<Expr>

The argument.

Let

Let-binding.

Fields

name: VarName

The bound name.

value: Box<Expr>

The value being bound.

body: Box<Expr>

The body in which the binding is in scope.

Fix

Fixed-point binding.

Fields

name: VarName

The name bound to the fixed point inside body.

body: Box<Expr>

The expression being closed over its own name.

Ref

Allocate a fresh cell initialised with the value of inner.

Fields

inner: Box<Expr>

The expression whose value will populate the new cell.

Deref

Dereference the cell pointed to by inner.

Fields

inner: Box<Expr>

The expression that must evaluate to a Value::Ref.

Assign

Assign value into the cell or property pointed to by target. When target is a Expr::Field the assignment is to an own property of the referenced object; otherwise it is to a cell.

Fields

target: Box<Expr>

The expression denoting the location to be written.

value: Box<Expr>

The value to store.

Seq

Sequence: evaluate first (discarding its value), then evaluate second and return its value.

Fields

first: Box<Expr>

The expression evaluated for effect only.

second: Box<Expr>

The expression whose value is the result of the sequence.

Object

Object literal with optional prototype. Evaluating an Expr::Object allocates a fresh object on the heap and returns a reference to it.

Fields

entries: Vec<(VarName, Expr)>

Property entries, in source order. Duplicates resolve by the last write.

prototype: Option<Box<Expr>>

Optional prototype expression. When Some, the value must evaluate to a reference to another object at run time.

Field

Field access on an object. Walks the prototype chain on miss.

Fields

object: Box<Expr>

The object expression.

name: VarName

The property name to look up.

Throw

Throw an exception carrying the value of inner. Unwinds the current evaluation until caught by an enclosing Expr::TryCatch.

Fields

inner: Box<Expr>

The value to throw.

TryCatch

Catch an exception thrown by body, binding the thrown value to catch_param while evaluating handler.

Fields

body: Box<Expr>

The expression evaluated under exception protection.

catch_param: VarName

The name to which a caught thrown value is bound.

handler: Box<Expr>

The handler expression evaluated when body throws.

Implementations

impl Expr

pub fn var(name: impl Into<VarName>) -> Self

Build a variable reference.

pub fn lam(param: impl Into<VarName>, body: Self) -> Self

Build a lambda abstraction.

pub fn app(func: Self, arg: Self) -> Self

Build an application node.

pub fn bind(name: impl Into<VarName>, value: Self, body: Self) -> Self

Build a let-binding. Named bind because let is a keyword.

pub fn fix(name: impl Into<VarName>, body: Self) -> Self

Build a fixed-point binding.

pub fn alloc(inner: Self) -> Self

Build a ref allocation node.

pub fn deref(inner: Self) -> Self

Build a dereference node.

pub fn assign(target: Self, value: Self) -> Self

Build an assignment node.

pub fn seq(first: Self, second: Self) -> Self

Build a sequence node.

pub fn object(entries: Vec<(VarName, Self)>) -> Self

Build an object literal with no prototype.

pub fn object_with_proto(entries: Vec<(VarName, Self)>, prototype: Self) -> Self

Build an object literal with a prototype expression.

pub fn field(object: Self, name: impl Into<VarName>) -> Self

Build a field access node.

pub fn throw(inner: Self) -> Self

Build a throw node.

pub fn try_catch( body: Self, catch_param: impl Into<VarName>, handler: Self, ) -> Self

Build a try-catch node.

Trait Implementations

impl Clone for Expr

fn clone(&self) -> Expr

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Expr

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

Formats the value using the given formatter.

impl Display for Expr

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

Formats the value using the given formatter.

impl PartialEq for Expr

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for Expr

impl StructuralPartialEq for Expr