Struct chalk_ir::fold::shift::DownShifter

struct DownShifter<I> {
    target_binder: DebruijnIndex,
    interner: I,
}

A shifter that reduces debruijn indices – in other words, which lifts a value out from binders. Consider this example:

Fields

target_binder: DebruijnIndex

interner: I

Implementations

impl<I> DownShifter<I>

fn adjust( &self, bound_var: BoundVar, outer_binder: DebruijnIndex, ) -> Fallible<BoundVar>

Given a reference to a free variable at depth depth (appearing within binders internal binders), attempts to lift that free variable out from adjustment levels of binders (i.e., convert it to depth depth - self.adjustment). If the free variable is bound by one of those internal binders (i.e., depth < self.adjustment) the this will fail with Err. Otherwise, returns the variable at this new depth (but adjusted to appear within binders).

Trait Implementations

impl<I: Interner> FallibleTypeFolder<I> for DownShifter<I>

type Error = NoSolution

The type this folder returns when folding fails. This is commonly NoSolution.

fn as_dyn(&mut self) -> &mut dyn FallibleTypeFolder<I, Error = Self::Error>

Creates a dyn value from this folder. Unfortunately, this must be added manually to each impl of FallibleTypeFolder; it permits the default implements below to create a &mut dyn FallibleTypeFolder from Self without knowing what Self is (by invoking this method). Effectively, this limits impls of FallibleTypeFolder to types for which we are able to create a dyn value (i.e., not [T] types).

fn try_fold_free_var_ty( &mut self, bound_var: BoundVar, outer_binder: DebruijnIndex, ) -> Fallible<Ty<I>>

Invoked for TyKind::BoundVar instances that are not bound within the type being folded over:

fn try_fold_free_var_lifetime( &mut self, bound_var: BoundVar, outer_binder: DebruijnIndex, ) -> Fallible<Lifetime<I>>

As try_fold_free_var_ty, but for lifetimes.

fn try_fold_free_var_const( &mut self, ty: Ty<I>, bound_var: BoundVar, outer_binder: DebruijnIndex, ) -> Fallible<Const<I>>

As try_fold_free_var_ty, but for constants.

fn interner(&self) -> I

Gets the interner that is being folded from.

fn try_fold_ty( &mut self, ty: Ty<I>, outer_binder: DebruijnIndex, ) -> Result<Ty<I>, Self::Error>

Top-level callback: invoked for each Ty<I> that is encountered when folding. By default, invokes try_super_fold_with, which will in turn invoke the more specialized folding methods below, like try_fold_free_var_ty.

fn try_fold_lifetime( &mut self, lifetime: Lifetime<I>, outer_binder: DebruijnIndex, ) -> Result<Lifetime<I>, Self::Error>

Top-level callback: invoked for each Lifetime<I> that is encountered when folding. By default, invokes try_super_fold_with, which will in turn invoke the more specialized folding methods below, like try_fold_free_var_lifetime.

fn try_fold_const( &mut self, constant: Const<I>, outer_binder: DebruijnIndex, ) -> Result<Const<I>, Self::Error>

Top-level callback: invoked for each Const<I> that is encountered when folding. By default, invokes try_super_fold_with, which will in turn invoke the more specialized folding methods below, like try_fold_free_var_const.

fn try_fold_program_clause( &mut self, clause: ProgramClause<I>, outer_binder: DebruijnIndex, ) -> Result<ProgramClause<I>, Self::Error>

Invoked for every program clause. By default, recursively folds the goals contents.

fn try_fold_goal( &mut self, goal: Goal<I>, outer_binder: DebruijnIndex, ) -> Result<Goal<I>, Self::Error>

Invoked for every goal. By default, recursively folds the goals contents.

fn forbid_free_vars(&self) -> bool

If overridden to return true, then folding will panic if a free variable is encountered. This should be done if free type/lifetime variables are not expected.

fn forbid_free_placeholders(&self) -> bool

If overridden to return true, we will panic when a free placeholder type/lifetime/const is encountered.

fn try_fold_free_placeholder_ty( &mut self, universe: PlaceholderIndex, outer_binder: DebruijnIndex, ) -> Result<Ty<I>, Self::Error>

Invoked for each occurrence of a placeholder type; these are used when we instantiate binders universally. Returns a type to use instead, which should be suitably shifted to account for binders.

fn try_fold_free_placeholder_lifetime( &mut self, universe: PlaceholderIndex, outer_binder: DebruijnIndex, ) -> Result<Lifetime<I>, Self::Error>

As with try_fold_free_placeholder_ty, but for lifetimes.

fn try_fold_free_placeholder_const( &mut self, ty: Ty<I>, universe: PlaceholderIndex, outer_binder: DebruijnIndex, ) -> Result<Const<I>, Self::Error>

As with try_fold_free_placeholder_ty, but for constants.

fn forbid_inference_vars(&self) -> bool

If overridden to return true, inference variables will trigger panics when folded. Used when inference variables are unexpected.

fn try_fold_inference_ty( &mut self, var: InferenceVar, kind: TyVariableKind, outer_binder: DebruijnIndex, ) -> Result<Ty<I>, Self::Error>

Invoked for each occurrence of a inference type; these are used when we instantiate binders universally. Returns a type to use instead, which should be suitably shifted to account for binders.

fn try_fold_inference_lifetime( &mut self, var: InferenceVar, outer_binder: DebruijnIndex, ) -> Result<Lifetime<I>, Self::Error>

As with try_fold_inference_ty, but for lifetimes.

fn try_fold_inference_const( &mut self, ty: Ty<I>, var: InferenceVar, outer_binder: DebruijnIndex, ) -> Result<Const<I>, Self::Error>

As with try_fold_inference_ty, but for constants.