Struct chalk_engine::FlounderedSubgoal

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pub struct FlounderedSubgoal<I: Interner> {
    pub floundered_literal: Literal<I>,
    pub floundered_time: TimeStamp,
}
Expand description

A “floundered” subgoal is one that contains unbound existential variables for which it cannot produce a value. The classic example of floundering is a negative subgoal:

not { Implemented(?T: Foo) }

The way the prolog solver works, it basically enumerates all the ways that a given goal can be true. But we can’t use this technique to find all the ways that ?T: Foo can be false – so we call it floundered. In other words, we can evaluate a negative goal, but only if we know what ?T is – we can’t use the negative goal to help us figuring out ?T.

In addition to negative goals, we use floundering to prevent the trait solver from trying to enumerate very large goals with tons of answers. For example, we consider a goal like ?T: Sized to “flounder”, since we can’t hope to enumerate all types that are Sized. The same is true for other special traits like Clone.

Floundering can also occur indirectly. For example:

trait Foo { }
impl<T> Foo for T { }

trying to solve ?T: Foo would immediately require solving ?T: Sized, and hence would flounder.

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§floundered_literal: Literal<I>

Literal that floundered.

§floundered_time: TimeStamp

Current value of the strand’s clock at the time of floundering.

Trait Implementations§

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impl<I: Clone + Interner> Clone for FlounderedSubgoal<I>

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fn clone(&self) -> FlounderedSubgoal<I>

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<I: Debug + Interner> Debug for FlounderedSubgoal<I>

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

Formats the value using the given formatter. Read more
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impl<I: Hash + Interner> Hash for FlounderedSubgoal<I>

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

Feeds this value into the given Hasher. Read more
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fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl<I: PartialEq + Interner> PartialEq for FlounderedSubgoal<I>

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fn eq(&self, other: &FlounderedSubgoal<I>) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<I: Interner> TypeFoldable<I> for FlounderedSubgoal<I>

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fn try_fold_with<E>( self, folder: &mut dyn FallibleTypeFolder<I, Error = E>, outer_binder: DebruijnIndex, ) -> Result<Self, E>

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.
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fn fold_with( self, folder: &mut dyn TypeFolder<I, Error = Infallible>, outer_binder: DebruijnIndex, ) -> Self

A convenient alternative to try_fold_with for use with infallible folders. Do not override this method, to ensure coherence with try_fold_with.
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impl<I: Interner> TypeVisitable<I> for FlounderedSubgoal<I>

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fn visit_with<B>( &self, visitor: &mut dyn TypeVisitor<I, BreakTy = B>, outer_binder: DebruijnIndex, ) -> ControlFlow<B>

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.
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impl<I: Eq + Interner> Eq for FlounderedSubgoal<I>

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impl<I: Interner> StructuralPartialEq for FlounderedSubgoal<I>

Auto Trait Implementations§

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impl<I> Freeze for FlounderedSubgoal<I>
where <I as Interner>::InternedGoal: Freeze, <I as Interner>::InternedProgramClauses: Freeze,

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impl<I> RefUnwindSafe for FlounderedSubgoal<I>
where <I as Interner>::InternedGoal: RefUnwindSafe, <I as Interner>::InternedProgramClauses: RefUnwindSafe,

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impl<I> Send for FlounderedSubgoal<I>
where <I as Interner>::InternedGoal: Send, <I as Interner>::InternedProgramClauses: Send,

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impl<I> Sync for FlounderedSubgoal<I>
where <I as Interner>::InternedGoal: Sync, <I as Interner>::InternedProgramClauses: Sync,

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impl<I> Unpin for FlounderedSubgoal<I>
where <I as Interner>::InternedGoal: Unpin, <I as Interner>::InternedProgramClauses: Unpin,

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impl<I> UnwindSafe for FlounderedSubgoal<I>
where <I as Interner>::InternedGoal: UnwindSafe, <I as Interner>::InternedProgramClauses: UnwindSafe,

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> Cast for T

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fn cast<U>(self, interner: <U as HasInterner>::Interner) -> U
where Self: CastTo<U>, U: HasInterner,

Cast a value to type U using CastTo.
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impl<T> CloneToUninit for T
where T: Clone,

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default unsafe fn clone_to_uninit(&self, dst: *mut T)

🔬This is a nightly-only experimental API. (clone_to_uninit)
Performs copy-assignment from self to dst. Read more
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Checks if this value is equivalent to the given key. Read more
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Compare self to key and return true if they are equal.
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> Instrument for T

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fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided [Span], returning an Instrumented wrapper. Read more
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fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T, I> Shift<I> for T
where T: TypeFoldable<I>, I: Interner,

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fn shifted_in(self, interner: I) -> T

Shifts this term in one level of binders.
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fn shifted_in_from(self, interner: I, source_binder: DebruijnIndex) -> T

Shifts a term valid at outer_binder so that it is valid at the innermost binder. See [DebruijnIndex::shifted_in_from] for a detailed explanation.
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fn shifted_out_to( self, interner: I, target_binder: DebruijnIndex, ) -> Result<T, NoSolution>

Shifts a term valid at the innermost binder so that it is valid at outer_binder. See [DebruijnIndex::shifted_out_to] for a detailed explanation.
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fn shifted_out(self, interner: I) -> Result<T, NoSolution>

Shifts this term out one level of binders.
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impl<T> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<T, I> VisitExt<I> for T
where I: Interner, T: TypeVisitable<I>,

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fn has_free_vars(&self, interner: I) -> bool

Check whether there are free (non-bound) variables.
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impl<T> WithSubscriber for T

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fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a [WithDispatch] wrapper. Read more
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fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a [WithDispatch] wrapper. Read more