Struct chalk_ir::DebruijnIndex

pub struct DebruijnIndex { /* fields omitted */ }

References the binder at the given depth. The index is a de Bruijn index, so it counts back through the in-scope binders, with 0 being the innermost binder. This is used in impls and the like. For example, if we had a rule like for<T> { (T: Clone) :- (T: Copy) }, then T would be represented as a BoundVar(0) (as the for is the innermost binder).

Implementations

impl DebruijnIndex

pub const INNERMOST: DebruijnIndex

Innermost index.

pub const ONE: DebruijnIndex

One level higher than the innermost index.

pub fn new(depth: u32) -> Self

Creates a new de Bruijn index with a given depth.

pub fn depth(self) -> u32

Depth of the De Bruijn index, counting from 0 starting with the innermost binder.

pub fn within(self, outer_binder: DebruijnIndex) -> bool

True if the binder identified by this index is within the binder identified by the index outer_binder.

Example

Imagine you have the following binders in scope

forall<a> forall<b> forall<c>

then the Debruijn index for c would be 0, the index for b would be 1, and so on. Now consider the following calls:

• c.within(a) = true
• b.within(a) = true
• a.within(a) = false
• a.within(c) = false

#[must_use]

pub fn shifted_in(self) -> DebruijnIndex

Returns the resulting index when this value is moved into through one binder.

pub fn shift_in(&mut self)

Update this index in place by shifting it “in” through amount number of binders.

#[must_use]

pub fn shifted_in_from(self, outer_binder: DebruijnIndex) -> DebruijnIndex

Adds outer_binder levels to the self index. Intuitively, this shifts the self index, which was valid at the outer binder, so that it is valid at the innermost binder.

Example: Assume that the following binders are in scope:

for<A> for<B> for<C> for<D>
           ^ outer binder

Assume further that the outer_binder argument is 2, which means that it is referring to the for<B> binder (since D would be the innermost binder).

This means that self is relative to the binder B – so if self is 0 (INNERMOST), then it refers to B, and if self is 1, then it refers to A.

We will return as follows:

• 0.shifted_in_from(2) = 2 – i.e., B, when shifted in to the binding level D, has index 2
• 1.shifted_in_from(2) = 3 – i.e., A, when shifted in to the binding level D, has index 3
• 2.shifted_in_from(1) = 3 – here, we changed the outer_binder to refer to C. Therefore 2 (relative to C) refers to A, so the result is still 3 (since A, relative to the innermost binder, has index 3).

#[must_use]

pub fn shifted_out(self) -> Option<DebruijnIndex>

Returns the resulting index when this value is moved out from amount number of new binders.

pub fn shift_out(&mut self)

Update in place by shifting out from amount binders.

pub fn shifted_out_to(
    self,
    outer_binder: DebruijnIndex
) -> Option<DebruijnIndex>

Subtracts outer_binder levels from the self index. Intuitively, this shifts the self index, which was valid at the innermost binder, to one that is valid at the binder outer_binder.

This will return None if the self index is internal to the outer binder (i.e., if self < outer_binder).

Example: Assume that the following binders are in scope:

for<A> for<B> for<C> for<D>
           ^ outer binder

Assume further that the outer_binder argument is 2, which means that it is referring to the for<B> binder (since D would be the innermost binder).

This means that the result is relative to the binder B – so if self is 0 (INNERMOST), then it refers to B, and if self is 1, then it refers to A.

We will return as follows:

• 1.shifted_out_to(2) = None – i.e., the binder for C can’t be named from the binding level B
• 3.shifted_out_to(2) = Some(1) – i.e., A, when shifted out to the binding level B, has index 1

Trait Implementations

impl Clone for DebruijnIndex

fn clone(&self) -> DebruijnIndex

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for DebruijnIndex

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

Formats the value using the given formatter.

impl<I: Interner> Fold<I> for DebruijnIndex

type Result = Self

The type of value that will be produced once folding is done. Typically this is Self, unless Self contains borrowed values, in which case owned values are produced (for example, one can fold over a &T value where T: Fold, in which case you get back a T, not a &T).

fn fold_with<'i>(
    self,
    _folder: &mut dyn Folder<'i, I>,
    _outer_binder: DebruijnIndex
) -> Fallible<Self::Result> where
    I: 'i, 

Apply the given folder folder to self; binders is the number of binders that are in scope when beginning the folder. Typically binders starts as 0, but is adjusted when we encounter Binders<T> in the IR or other similar constructs.

impl Hash for DebruijnIndex

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, 

Feeds a slice of this type into the given Hasher.

impl Ord for DebruijnIndex

fn cmp(&self, other: &DebruijnIndex) -> Ordering

This method returns an Ordering between self and other.

#[must_use]

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

#[must_use]

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

#[must_use]

fn clamp(self, min: Self, max: Self) -> Self

Restrict a value to a certain interval.

impl PartialEq<DebruijnIndex> for DebruijnIndex

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

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

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

This method tests for !=.

impl PartialOrd<DebruijnIndex> for DebruijnIndex

fn partial_cmp(&self, other: &DebruijnIndex) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

#[must_use]

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

This method tests less than (for self and other) and is used by the < operator.

#[must_use]

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

This method tests less than or equal to (for self and other) and is used by the <= operator.

#[must_use]

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

This method tests greater than (for self and other) and is used by the > operator.

#[must_use]

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

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl<I: Interner> Visit<I> for DebruijnIndex

fn visit_with<'i, B>(
    &self,
    _visitor: &mut dyn Visitor<'i, I, BreakTy = B>,
    _outer_binder: DebruijnIndex
) -> ControlFlow<B> where
    I: 'i, 

Apply the given visitor visitor to self; binders is the number of binders that are in scope when beginning the visitor. Typically binders starts as 0, but is adjusted when we encounter Binders<T> in the IR or other similar constructs.

impl Copy for DebruijnIndex

impl Eq for DebruijnIndex

impl StructuralEq for DebruijnIndex

impl StructuralPartialEq for DebruijnIndex