Struct polytype::Context

pub struct Context { /* fields omitted */ }

Context is a type environment, keeping track of substitutions and type variables. Useful for unifying (and inferring) types.

Methods

impl Context

fn substitutions(&self) -> &HashMap<u32, Type>

fn extend(&mut self, v: u32, t: Type)

Create a new substitution for the type variable numbered v to the type t.

fn new_variable(&mut self) -> Type

Create a new Type::Variable from the next unused number.

fn unify(&mut self, t1: &Type, t2: &Type) -> Result<(), UnificationError>

Create constraints within the context that ensure the two types unify.

Examples

let mut ctx = Context::default();

let tbool = Type::Constructed("bool", vec![]);
let tint = Type::Constructed("int", vec![]);
fn tlist(tp: Type) -> Type {
    Type::Constructed("list", vec![Box::new(tp)])
}

let t1 = tlist(Type::from(Arrow::new(tint, Type::Variable(0))));
let t2 = tlist(Type::from(Arrow::new(Type::Variable(1), tbool)));
ctx.unify(&t1, &t2).expect("unifies");

let t1 = t1.apply(&ctx);
let t2 = t2.apply(&ctx);
assert_eq!(t1, t2);

Trait Implementations

impl Debug for Context

fn fmt(&self, __arg_0: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Clone for Context

fn clone(&self) -> Context

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Default for Context

fn default() -> Self

Returns the "default value" for a type.