Enum polytype::TypeSchema

pub enum TypeSchema<N: Name = &'static str> {
    Monotype(Type<N>),
    Polytype {
        variable: Variable,
        body: Box<TypeSchema<N>>,
    },
}

Represents polytypes (uninstantiated, universally quantified types).

The primary ways of creating a TypeSchema are with the ptp! macro or with Type::generalize.

Variants

Monotype(Type<N>)

Non-polymorphic types (e.g. α → β, int → bool)

Polytype

Polymorphic types (e.g. ∀α. α → α, ∀α. ∀β. α → β)

Fields of Polytype

variable: Variable	The Variable being bound
body: Box<TypeSchema<N>>	The type in which variable is bound

Methods

impl<N: Name> TypeSchema<N>

pub fn is_bound(&self, v: Variable) -> bool

Checks whether a variable is bound in the quantification of a polytype.

Examples

let t = ptp!(0; @arrow[tp!(0), tp!(1)]); // ∀α. α → β
assert!(t.is_bound(0));
assert!(!t.is_bound(1));

pub fn bound_vars(&self) -> Vec<Variable>

Returns a set of each Variable bound by the TypeSchema.

Examples

let t = ptp!(0, 1; @arrow[tp!(1), tp!(2), tp!(3)]); // ∀α. ∀β. β → ɣ → δ
assert_eq!(t.bound_vars(), vec![0, 1]);

pub fn free_vars(&self) -> Vec<Variable>

Returns a set of each free Variable in the TypeSchema.

Examples

let t = ptp!(0, 1; @arrow[tp!(1), tp!(2), tp!(3)]); // ∀α. ∀β. β → ɣ → δ
let mut free = t.free_vars();
free.sort();
assert_eq!(free, vec![2, 3]);

pub fn instantiate(&self, ctx: &mut Context<N>) -> Type<N>

Instantiate a TypeSchema in the context by removing quantifiers.

All type variables will be replaced with fresh type variables.

Examples

let mut ctx = Context::default();

let t1 = ptp!(3; list(tp!(3)));
let t2 = ptp!(3; list(tp!(3)));

let t1 = t1.instantiate(&mut ctx);
let t2 = t2.instantiate(&mut ctx);
assert_eq!(t1.to_string(), "list(t0)");
assert_eq!(t2.to_string(), "list(t1)");

pub fn instantiate_owned(self, ctx: &mut Context<N>) -> Type<N>

Like instantiate, but works in-place.

pub fn parse(s: &str) -> Result<TypeSchema<N>, ()>

Parse a TypeSchema from a string. This round-trips with Display. This is a leaky operation and should be avoided wherever possible: names of constructed types will remain until program termination.

The "for-all" ∀ is optional.

Examples

let t_par = TypeSchema::parse("∀t0. t0 -> t0").expect("valid type");
let t_lit = ptp!(0; @arrow[tp!(0), tp!(0)]);
assert_eq!(t_par, t_lit);

let s = "∀t0. ∀t1. (t1 → t0 → t1) → t1 → list(t0) → t1";
let t: TypeSchema<&'static str> = TypeSchema::parse(s).expect("valid type");
let round_trip = t.to_string();
assert_eq!(s, round_trip);

Trait Implementations

impl<N: Debug + Name> Debug for TypeSchema<N>

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

Formats the value using the given formatter.

impl<N: Clone + Name> Clone for TypeSchema<N>

fn clone(&self) -> TypeSchema<N>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<N: Hash + Name> Hash for TypeSchema<N>

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

Feeds this value into the given [Hasher].

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

Feeds a slice of this type into the given [Hasher].

impl<N: PartialEq + Name> PartialEq for TypeSchema<N>

fn eq(&self, other: &TypeSchema<N>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &TypeSchema<N>) -> bool

This method tests for !=.

impl<N: Eq + Name> Eq for TypeSchema<N>

impl<N: Name> Display for TypeSchema<N>

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

Formats the value using the given formatter.