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Consistently use a Witness rather than an expression to represent a possibly-symbolic witness. (#2245)

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Previously we used an expression in some places and a `Witness` values in others. The eventual goal is to make `Witness` values behave like other symbolic values such as `NominalClassType`, but the first step is to consistently treat them like values rather than expressions.

No functionality change intended.
This commit is contained in:
Richard Smith
2022-10-03 14:00:41 -07:00
committed by GitHub
parent c198dafbe8
commit 04d49cebd8
11 changed files with 222 additions and 152 deletions
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explorer/interpreter/interpreter.cpp
+32 -5
View File
@@ -79,6 +79,8 @@ class Interpreter {
auto StepExp() -> ErrorOr<Success>;
// State transitions for lvalues.
auto StepLvalue() -> ErrorOr<Success>;
// State transitions for witnesses.
auto StepWitness() -> ErrorOr<Success>;
// State transitions for patterns.
auto StepPattern() -> ErrorOr<Success>;
// State transition for statements.
@@ -897,7 +899,7 @@ auto Interpreter::StepExp() -> ErrorOr<Success> {
const InstantiateImpl& inst_impl = cast<InstantiateImpl>(exp);
if (act.pos() == 0) {
return todo_.Spawn(
std::make_unique<ExpressionAction>(inst_impl.generic_impl()));
std::make_unique<WitnessAction>(inst_impl.generic_impl()));
}
if (act.pos() == 1 && isa<SymbolicWitness>(act.results()[0])) {
return todo_.FinishAction(arena_->New<SymbolicWitness>(&exp));
@@ -905,7 +907,8 @@ auto Interpreter::StepExp() -> ErrorOr<Success> {
if (act.pos() - 1 < int(inst_impl.impls().size())) {
auto iter = inst_impl.impls().begin();
std::advance(iter, act.pos() - 1);
return todo_.Spawn(std::make_unique<ExpressionAction>(iter->second));
return todo_.Spawn(
std::make_unique<WitnessAction>(cast<Witness>(iter->second)));
} else {
Nonnull<const ImplWitness*> generic_witness =
cast<ImplWitness>(act.results()[0]);
@@ -997,7 +1000,7 @@ auto Interpreter::StepExp() -> ErrorOr<Success> {
// Next, if we're accessing an interface member, evaluate the `impl`
// expression to find the corresponding witness.
return todo_.Spawn(
std::make_unique<ExpressionAction>(access.impl().value()));
std::make_unique<WitnessAction>(access.impl().value()));
} else {
// Finally, produce the result.
std::optional<Nonnull<const InterfaceType*>> found_in_interface =
@@ -1058,7 +1061,7 @@ auto Interpreter::StepExp() -> ErrorOr<Success> {
// Next, if we're accessing an interface member, evaluate the `impl`
// expression to find the corresponding witness.
return todo_.Spawn(
std::make_unique<ExpressionAction>(access.impl().value()));
std::make_unique<WitnessAction>(access.impl().value()));
} else {
// Finally, produce the result.
std::optional<Nonnull<const InterfaceType*>> found_in_interface =
@@ -1181,7 +1184,8 @@ auto Interpreter::StepExp() -> ErrorOr<Success> {
} else if (num_impls > 0 && act.pos() < 2 + int(num_impls)) {
auto iter = call.impls().begin();
std::advance(iter, act.pos() - 2);
return todo_.Spawn(std::make_unique<ExpressionAction>(iter->second));
return todo_.Spawn(
std::make_unique<WitnessAction>(cast<Witness>(iter->second)));
} else if (act.pos() == 2 + int(num_impls)) {
// { { v2 :: v1([]) :: C, E, F} :: S, H}
// -> { {C',E',F'} :: {C, E, F} :: S, H}
@@ -1435,6 +1439,26 @@ auto Interpreter::StepExp() -> ErrorOr<Success> {
} // switch (exp->kind)
}
auto Interpreter::StepWitness() -> ErrorOr<Success> {
Action& act = todo_.CurrentAction();
const Witness* witness = cast<WitnessAction>(act).witness();
if (trace_stream_) {
**trace_stream_ << "--- step witness " << *witness << " ." << act.pos()
<< ". --->\n";
}
switch (witness->kind()) {
case Value::Kind::SymbolicWitness:
return todo_.ReplaceWith(std::make_unique<ExpressionAction>(
&cast<SymbolicWitness>(witness)->impl_expression()));
case Value::Kind::ImplWitness:
return todo_.FinishAction(witness);
default:
CARBON_FATAL() << "unexpected kind of witness " << *witness;
}
}
auto Interpreter::StepPattern() -> ErrorOr<Success> {
Action& act = todo_.CurrentAction();
const Pattern& pattern = cast<PatternAction>(act).pattern();
@@ -1940,6 +1964,9 @@ auto Interpreter::Step() -> ErrorOr<Success> {
case Action::Kind::ExpressionAction:
CARBON_RETURN_IF_ERROR(StepExp());
break;
case Action::Kind::WitnessAction:
CARBON_RETURN_IF_ERROR(StepWitness());
break;
case Action::Kind::PatternAction:
CARBON_RETURN_IF_ERROR(StepPattern());
break;