Struct chalk_engine::FlounderedSubgoal
source · 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.
Fields§
§floundered_literal: Literal<I>
Literal that floundered.
floundered_time: TimeStamp
Current value of the strand’s clock at the time of floundering.
Trait Implementations§
source§impl<I: Clone + Interner> Clone for FlounderedSubgoal<I>
impl<I: Clone + Interner> Clone for FlounderedSubgoal<I>
source§fn clone(&self) -> FlounderedSubgoal<I>
fn clone(&self) -> FlounderedSubgoal<I>
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read moresource§impl<I: Debug + Interner> Debug for FlounderedSubgoal<I>
impl<I: Debug + Interner> Debug for FlounderedSubgoal<I>
source§impl<I: Hash + Interner> Hash for FlounderedSubgoal<I>
impl<I: Hash + Interner> Hash for FlounderedSubgoal<I>
source§impl<I: PartialEq + Interner> PartialEq for FlounderedSubgoal<I>
impl<I: PartialEq + Interner> PartialEq for FlounderedSubgoal<I>
source§fn eq(&self, other: &FlounderedSubgoal<I>) -> bool
fn eq(&self, other: &FlounderedSubgoal<I>) -> bool
self
and other
values to be equal, and is used
by ==
.source§impl<I: Interner> TypeFoldable<I> for FlounderedSubgoal<I>
impl<I: Interner> TypeFoldable<I> for FlounderedSubgoal<I>
source§fn try_fold_with<E>(
self,
folder: &mut dyn FallibleTypeFolder<I, Error = E>,
outer_binder: DebruijnIndex,
) -> Result<Self, E>
fn try_fold_with<E>( self, folder: &mut dyn FallibleTypeFolder<I, Error = E>, outer_binder: DebruijnIndex, ) -> Result<Self, E>
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.§fn fold_with(
self,
folder: &mut dyn TypeFolder<I, Error = Infallible>,
outer_binder: DebruijnIndex,
) -> Self
fn fold_with( self, folder: &mut dyn TypeFolder<I, Error = Infallible>, outer_binder: DebruijnIndex, ) -> Self
try_fold_with
for use with infallible
folders. Do not override this method, to ensure coherence with
try_fold_with
.source§impl<I: Interner> TypeVisitable<I> for FlounderedSubgoal<I>
impl<I: Interner> TypeVisitable<I> for FlounderedSubgoal<I>
source§fn visit_with<B>(
&self,
visitor: &mut dyn TypeVisitor<I, BreakTy = B>,
outer_binder: DebruijnIndex,
) -> ControlFlow<B>
fn visit_with<B>( &self, visitor: &mut dyn TypeVisitor<I, BreakTy = B>, outer_binder: DebruijnIndex, ) -> ControlFlow<B>
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<I: Eq + Interner> Eq for FlounderedSubgoal<I>
impl<I: Interner> StructuralPartialEq for FlounderedSubgoal<I>
Auto Trait Implementations§
impl<I> Freeze for FlounderedSubgoal<I>
impl<I> RefUnwindSafe for FlounderedSubgoal<I>where
<I as Interner>::InternedGoal: RefUnwindSafe,
<I as Interner>::InternedProgramClauses: RefUnwindSafe,
impl<I> Send for FlounderedSubgoal<I>
impl<I> Sync for FlounderedSubgoal<I>
impl<I> Unpin for FlounderedSubgoal<I>
impl<I> UnwindSafe for FlounderedSubgoal<I>where
<I as Interner>::InternedGoal: UnwindSafe,
<I as Interner>::InternedProgramClauses: UnwindSafe,
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
§impl<T> Cast for T
impl<T> Cast for T
source§impl<T> CloneToUninit for Twhere
T: Clone,
impl<T> CloneToUninit for Twhere
T: Clone,
source§default unsafe fn clone_to_uninit(&self, dst: *mut T)
default unsafe fn clone_to_uninit(&self, dst: *mut T)
clone_to_uninit
)§impl<Q, K> Equivalent<K> for Q
impl<Q, K> Equivalent<K> for Q
§fn equivalent(&self, key: &K) -> bool
fn equivalent(&self, key: &K) -> bool
§impl<Q, K> Equivalent<K> for Q
impl<Q, K> Equivalent<K> for Q
§fn equivalent(&self, key: &K) -> bool
fn equivalent(&self, key: &K) -> bool
key
and return true
if they are equal.§impl<T> Instrument for T
impl<T> Instrument for T
§fn instrument(self, span: Span) -> Instrumented<Self>
fn instrument(self, span: Span) -> Instrumented<Self>
§fn in_current_span(self) -> Instrumented<Self>
fn in_current_span(self) -> Instrumented<Self>
§impl<T, I> Shift<I> for Twhere
T: TypeFoldable<I>,
I: Interner,
impl<T, I> Shift<I> for Twhere
T: TypeFoldable<I>,
I: Interner,
§fn shifted_in(self, interner: I) -> T
fn shifted_in(self, interner: I) -> T
§fn shifted_in_from(self, interner: I, source_binder: DebruijnIndex) -> T
fn shifted_in_from(self, interner: I, source_binder: DebruijnIndex) -> T
outer_binder
so that it is
valid at the innermost binder. See [DebruijnIndex::shifted_in_from
]
for a detailed explanation.§fn shifted_out_to(
self,
interner: I,
target_binder: DebruijnIndex,
) -> Result<T, NoSolution>
fn shifted_out_to( self, interner: I, target_binder: DebruijnIndex, ) -> Result<T, NoSolution>
outer_binder
. See [DebruijnIndex::shifted_out_to
]
for a detailed explanation.