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d71f5b1784da9fb4ad403fde3a8d1d25a0e9d624
carbon-lang/executable_semantics/interpreter/interpreter.cpp
T
Geoff Romer d71f5b1784 Express stack updates using return values. (#747) 
This enables the interpreter logic to express its intent more directly, especially in the common cases, and enables us to get rid of ValAction. It's also a step toward simplifying and encapsulating `state->stack`.
2021-08-19 13:35:47 -07:00

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// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "executable_semantics/interpreter/interpreter.h"
#include <iterator>
#include <list>
#include <map>
#include <optional>
#include <utility>
#include <variant>
#include <vector>
#include "common/check.h"
#include "executable_semantics/ast/expression.h"
#include "executable_semantics/ast/function_definition.h"
#include "executable_semantics/common/arena.h"
#include "executable_semantics/common/error.h"
#include "executable_semantics/common/tracing_flag.h"
#include "executable_semantics/interpreter/action.h"
#include "executable_semantics/interpreter/frame.h"
#include "executable_semantics/interpreter/stack.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Support/Casting.h"
using llvm::cast;
using llvm::dyn_cast;
namespace Carbon {
State* state = nullptr;
void Step();
//
// Auxiliary Functions
//
void PrintEnv(Env values, llvm::raw_ostream& out) {
llvm::ListSeparator sep;
for (const auto& [name, address] : values) {
out << sep << name << ": ";
state->heap.PrintAddress(address, out);
}
}
//
// State Operations
//
void PrintStack(const Stack<Ptr<Frame>>& ls, llvm::raw_ostream& out) {
llvm::ListSeparator sep(" :: ");
for (const auto& frame : ls) {
out << sep << *frame;
}
}
auto CurrentEnv(State* state) -> Env {
Ptr<Frame> frame = state->stack.Top();
return frame->scopes.Top()->values;
}
// Returns the given name from the environment, printing an error if not found.
static auto GetFromEnv(int line_num, const std::string& name) -> Address {
std::optional<Address> pointer = CurrentEnv(state).Get(name);
if (!pointer) {
FATAL_RUNTIME_ERROR(line_num) << "could not find `" << name << "`";
}
return *pointer;
}
void PrintState(llvm::raw_ostream& out) {
out << "{\nstack: ";
PrintStack(state->stack, out);
out << "\nheap: " << state->heap;
if (!state->stack.IsEmpty() && !state->stack.Top()->scopes.IsEmpty()) {
out << "\nvalues: ";
PrintEnv(CurrentEnv(state), out);
}
out << "\n}\n";
}
auto EvalPrim(Operator op, const std::vector<const Value*>& args, int line_num)
-> const Value* {
switch (op) {
case Operator::Neg:
return global_arena->RawNew<IntValue>(-cast<IntValue>(*args[0]).Val());
case Operator::Add:
return global_arena->RawNew<IntValue>(cast<IntValue>(*args[0]).Val() +
cast<IntValue>(*args[1]).Val());
case Operator::Sub:
return global_arena->RawNew<IntValue>(cast<IntValue>(*args[0]).Val() -
cast<IntValue>(*args[1]).Val());
case Operator::Mul:
return global_arena->RawNew<IntValue>(cast<IntValue>(*args[0]).Val() *
cast<IntValue>(*args[1]).Val());
case Operator::Not:
return global_arena->RawNew<BoolValue>(!cast<BoolValue>(*args[0]).Val());
case Operator::And:
return global_arena->RawNew<BoolValue>(cast<BoolValue>(*args[0]).Val() &&
cast<BoolValue>(*args[1]).Val());
case Operator::Or:
return global_arena->RawNew<BoolValue>(cast<BoolValue>(*args[0]).Val() ||
cast<BoolValue>(*args[1]).Val());
case Operator::Eq:
return global_arena->RawNew<BoolValue>(
ValueEqual(args[0], args[1], line_num));
case Operator::Ptr:
return global_arena->RawNew<PointerType>(args[0]);
case Operator::Deref:
FATAL() << "dereference not implemented yet";
}
}
// Globally-defined entities, such as functions, structs, choices.
static Env globals;
void InitEnv(const Declaration& d, Env* env) {
switch (d.Tag()) {
case Declaration::Kind::FunctionDeclaration: {
const FunctionDefinition& func_def =
cast<FunctionDeclaration>(d).Definition();
Env new_env = *env;
// Bring the deduced parameters into scope.
for (const auto& deduced : func_def.deduced_parameters) {
Address a = state->heap.AllocateValue(
global_arena->RawNew<VariableType>(deduced.name));
new_env.Set(deduced.name, a);
}
auto pt = InterpPattern(new_env, func_def.param_pattern);
auto f =
global_arena->RawNew<FunctionValue>(func_def.name, pt, func_def.body);
Address a = state->heap.AllocateValue(f);
env->Set(func_def.name, a);
break;
}
case Declaration::Kind::ClassDeclaration: {
const ClassDefinition& class_def = cast<ClassDeclaration>(d).Definition();
VarValues fields;
VarValues methods;
for (const Member* m : class_def.members) {
switch (m->Tag()) {
case Member::Kind::FieldMember: {
const BindingPattern* binding = cast<FieldMember>(*m).Binding();
const Expression* type_expression =
cast<ExpressionPattern>(binding->Type())->Expression();
auto type = InterpExp(Env(), type_expression);
fields.push_back(make_pair(*binding->Name(), type));
break;
}
}
}
auto st = global_arena->RawNew<ClassType>(
class_def.name, std::move(fields), std::move(methods));
auto a = state->heap.AllocateValue(st);
env->Set(class_def.name, a);
break;
}
case Declaration::Kind::ChoiceDeclaration: {
const auto& choice = cast<ChoiceDeclaration>(d);
VarValues alts;
for (const auto& [name, signature] : choice.Alternatives()) {
auto t = InterpExp(Env(), signature);
alts.push_back(make_pair(name, t));
}
auto ct =
global_arena->RawNew<ChoiceType>(choice.Name(), std::move(alts));
auto a = state->heap.AllocateValue(ct);
env->Set(choice.Name(), a);
break;
}
case Declaration::Kind::VariableDeclaration: {
const auto& var = cast<VariableDeclaration>(d);
// Adds an entry in `globals` mapping the variable's name to the
// result of evaluating the initializer.
auto v = InterpExp(*env, var.Initializer());
Address a = state->heap.AllocateValue(v);
env->Set(*var.Binding()->Name(), a);
break;
}
}
}
static void InitGlobals(const std::list<Ptr<const Declaration>>& fs) {
for (const auto d : fs) {
InitEnv(*d, &globals);
}
}
void DeallocateScope(Ptr<Scope> scope) {
for (const auto& l : scope->locals) {
std::optional<Address> a = scope->values.Get(l);
CHECK(a);
state->heap.Deallocate(*a);
}
}
void DeallocateLocals(Ptr<Frame> frame) {
while (!frame->scopes.IsEmpty()) {
DeallocateScope(frame->scopes.Top());
frame->scopes.Pop();
}
}
const Value* CreateTuple(Ptr<Action> act, const Expression* exp) {
// { { (v1,...,vn) :: C, E, F} :: S, H}
// -> { { `(v1,...,vn) :: C, E, F} :: S, H}
const auto& tup_lit = cast<TupleLiteral>(*exp);
CHECK(act->Results().size() == tup_lit.Fields().size());
std::vector<TupleElement> elements;
for (size_t i = 0; i < act->Results().size(); ++i) {
elements.push_back(
{.name = tup_lit.Fields()[i].name, .value = act->Results()[i]});
}
return global_arena->RawNew<TupleValue>(std::move(elements));
}
auto PatternMatch(const Value* p, const Value* v, int line_num)
-> std::optional<Env> {
switch (p->Tag()) {
case Value::Kind::BindingPlaceholderValue: {
const auto& placeholder = cast<BindingPlaceholderValue>(*p);
Env values;
if (placeholder.Name().has_value()) {
Address a = state->heap.AllocateValue(CopyVal(v, line_num));
values.Set(*placeholder.Name(), a);
}
return values;
}
case Value::Kind::TupleValue:
switch (v->Tag()) {
case Value::Kind::TupleValue: {
const auto& p_tup = cast<TupleValue>(*p);
const auto& v_tup = cast<TupleValue>(*v);
if (p_tup.Elements().size() != v_tup.Elements().size()) {
FATAL_PROGRAM_ERROR(line_num)
<< "arity mismatch in tuple pattern match:\n pattern: "
<< p_tup << "\n value: " << v_tup;
}
Env values;
for (size_t i = 0; i < p_tup.Elements().size(); ++i) {
if (p_tup.Elements()[i].name != v_tup.Elements()[i].name) {
FATAL_PROGRAM_ERROR(line_num)
<< "Tuple field name '" << v_tup.Elements()[i].name
<< "' does not match pattern field name '"
<< p_tup.Elements()[i].name << "'";
}
std::optional<Env> matches = PatternMatch(
p_tup.Elements()[i].value, v_tup.Elements()[i].value, line_num);
if (!matches) {
return std::nullopt;
}
for (const auto& [name, value] : *matches) {
values.Set(name, value);
}
} // for
return values;
}
default:
FATAL() << "expected a tuple value in pattern, not " << *v;
}
case Value::Kind::AlternativeValue:
switch (v->Tag()) {
case Value::Kind::AlternativeValue: {
const auto& p_alt = cast<AlternativeValue>(*p);
const auto& v_alt = cast<AlternativeValue>(*v);
if (p_alt.ChoiceName() != v_alt.ChoiceName() ||
p_alt.AltName() != v_alt.AltName()) {
return std::nullopt;
}
return PatternMatch(p_alt.Argument(), v_alt.Argument(), line_num);
}
default:
FATAL() << "expected a choice alternative in pattern, not " << *v;
}
case Value::Kind::FunctionType:
switch (v->Tag()) {
case Value::Kind::FunctionType: {
const auto& p_fn = cast<FunctionType>(*p);
const auto& v_fn = cast<FunctionType>(*v);
std::optional<Env> param_matches =
PatternMatch(p_fn.Param(), v_fn.Param(), line_num);
if (!param_matches) {
return std::nullopt;
}
std::optional<Env> ret_matches =
PatternMatch(p_fn.Ret(), v_fn.Ret(), line_num);
if (!ret_matches) {
return std::nullopt;
}
Env values = *param_matches;
for (const auto& [name, value] : *ret_matches) {
values.Set(name, value);
}
return values;
}
default:
return std::nullopt;
}
case Value::Kind::AutoType:
// `auto` matches any type, without binding any new names. We rely
// on the typechecker to ensure that `v` is a type.
return Env();
default:
if (ValueEqual(p, v, line_num)) {
return Env();
} else {
return std::nullopt;
}
}
}
void PatternAssignment(const Value* pat, const Value* val, int line_num) {
switch (pat->Tag()) {
case Value::Kind::PointerValue:
state->heap.Write(cast<PointerValue>(*pat).Val(), CopyVal(val, line_num),
line_num);
break;
case Value::Kind::TupleValue: {
switch (val->Tag()) {
case Value::Kind::TupleValue: {
const auto& pat_tup = cast<TupleValue>(*pat);
const auto& val_tup = cast<TupleValue>(*val);
if (pat_tup.Elements().size() != val_tup.Elements().size()) {
FATAL_RUNTIME_ERROR(line_num)
<< "arity mismatch in tuple pattern assignment:\n pattern: "
<< pat_tup << "\n value: " << val_tup;
}
for (const TupleElement& pattern_element : pat_tup.Elements()) {
const Value* value_field = val_tup.FindField(pattern_element.name);
if (value_field == nullptr) {
FATAL_RUNTIME_ERROR(line_num)
<< "field " << pattern_element.name << "not in " << *val;
}
PatternAssignment(pattern_element.value, value_field, line_num);
}
break;
}
default:
FATAL() << "expected a tuple value on right-hand-side, not " << *val;
}
break;
}
case Value::Kind::AlternativeValue: {
switch (val->Tag()) {
case Value::Kind::AlternativeValue: {
const auto& pat_alt = cast<AlternativeValue>(*pat);
const auto& val_alt = cast<AlternativeValue>(*val);
CHECK(val_alt.ChoiceName() == pat_alt.ChoiceName() &&
val_alt.AltName() == pat_alt.AltName())
<< "internal error in pattern assignment";
PatternAssignment(pat_alt.Argument(), val_alt.Argument(), line_num);
break;
}
default:
FATAL() << "expected an alternative in left-hand-side, not " << *val;
}
break;
}
default:
CHECK(ValueEqual(pat, val, line_num))
<< "internal error in pattern assignment";
}
}
// State transition functions
//
// The `Step*` family of functions implement state transitions in the
// interpreter by executing a step of the Action at the top of the todo stack,
// and then returning a Transition that specifies how `state.stack` should be
// updated. `Transition` is a variant of several "transition types" representing
// the different kinds of state transition.
// Transition type which indicates that the current Action is now done.
struct Done {
// The value computed by the Action. Should always be null for Statement
// Actions, and never null for any other kind of Action.
const Value* result = nullptr;
};
// Transition type which spawns a new Action on the todo stack above the current
// Action, and increments the current Action's position counter.
struct Spawn {
Ptr<Action> child;
};
// Transition type which spawns a new Action that replaces the current action
// on the todo stack.
struct Delegate {
Ptr<Action> delegate;
};
// Transition type which keeps the current Action at the top of the stack,
// and increments its position counter.
struct RunAgain {};
// Transition type which unwinds the `todo` and `scopes` stacks until it
// reaches a specified Action lower in the stack.
struct UnwindTo {
const Ptr<Action> new_top;
};
// Transition type which unwinds the entire current stack frame, and returns
// a specified value to the caller.
struct UnwindFunctionCall {
const Value* return_val;
};
// Transition type which removes the current action from the top of the todo
// stack, then creates a new stack frame which calls the specified function
// with the specified arguments.
struct CallFunction {
const FunctionValue* function;
const Value* args;
int line_num;
};
// Transition type which does nothing.
//
// TODO(geoffromer): This is a temporary placeholder during refactoring. All
// uses of this type should be replaced with meaningful transitions.
struct ManualTransition {};
using Transition =
std::variant<Done, Spawn, Delegate, RunAgain, UnwindTo, UnwindFunctionCall,
CallFunction, ManualTransition>;
// State transitions for lvalues.
Transition StepLvalue() {
Ptr<Action> act = state->stack.Top()->todo.Top();
const Expression* exp = cast<LValAction>(*act).Exp();
if (tracing_output) {
llvm::outs() << "--- step lvalue " << *exp << " --->\n";
}
switch (exp->Tag()) {
case Expression::Kind::IdentifierExpression: {
// { {x :: C, E, F} :: S, H}
// -> { {E(x) :: C, E, F} :: S, H}
Address pointer = GetFromEnv(exp->LineNumber(),
cast<IdentifierExpression>(*exp).Name());
const Value* v = global_arena->RawNew<PointerValue>(pointer);
return Done{v};
}
case Expression::Kind::FieldAccessExpression: {
if (act->Pos() == 0) {
// { {e.f :: C, E, F} :: S, H}
// -> { e :: [].f :: C, E, F} :: S, H}
return Spawn{global_arena->New<LValAction>(
cast<FieldAccessExpression>(*exp).Aggregate())};
} else {
// { v :: [].f :: C, E, F} :: S, H}
// -> { { &v.f :: C, E, F} :: S, H }
Address aggregate = cast<PointerValue>(*act->Results()[0]).Val();
Address field = aggregate.SubobjectAddress(
cast<FieldAccessExpression>(*exp).Field());
return Done{global_arena->RawNew<PointerValue>(field)};
}
}
case Expression::Kind::IndexExpression: {
if (act->Pos() == 0) {
// { {e[i] :: C, E, F} :: S, H}
// -> { e :: [][i] :: C, E, F} :: S, H}
return Spawn{global_arena->New<LValAction>(
cast<IndexExpression>(*exp).Aggregate())};
} else if (act->Pos() == 1) {
return Spawn{global_arena->New<ExpressionAction>(
cast<IndexExpression>(*exp).Offset())};
} else {
// { v :: [][i] :: C, E, F} :: S, H}
// -> { { &v[i] :: C, E, F} :: S, H }
Address aggregate = cast<PointerValue>(*act->Results()[0]).Val();
std::string f =
std::to_string(cast<IntValue>(*act->Results()[1]).Val());
Address field = aggregate.SubobjectAddress(f);
return Done{global_arena->RawNew<PointerValue>(field)};
}
}
case Expression::Kind::TupleLiteral: {
if (act->Pos() == 0) {
// { {(f1=e1,...) :: C, E, F} :: S, H}
// -> { {e1 :: (f1=[],...) :: C, E, F} :: S, H}
const Expression* e1 = cast<TupleLiteral>(*exp).Fields()[0].expression;
return Spawn{global_arena->New<LValAction>(e1)};
} else if (act->Pos() !=
static_cast<int>(cast<TupleLiteral>(*exp).Fields().size())) {
// { { vk :: (f1=v1,..., fk=[],fk+1=ek+1,...) :: C, E, F} :: S,
// H}
// -> { { ek+1 :: (f1=v1,..., fk=vk, fk+1=[],...) :: C, E, F} :: S,
// H}
const Expression* elt =
cast<TupleLiteral>(*exp).Fields()[act->Pos()].expression;
return Spawn{global_arena->New<LValAction>(elt)};
} else {
return Done{CreateTuple(act, exp)};
}
}
case Expression::Kind::IntLiteral:
case Expression::Kind::BoolLiteral:
case Expression::Kind::CallExpression:
case Expression::Kind::PrimitiveOperatorExpression:
case Expression::Kind::IntTypeLiteral:
case Expression::Kind::BoolTypeLiteral:
case Expression::Kind::TypeTypeLiteral:
case Expression::Kind::FunctionTypeLiteral:
case Expression::Kind::ContinuationTypeLiteral:
case Expression::Kind::StringLiteral:
case Expression::Kind::StringTypeLiteral:
case Expression::Kind::IntrinsicExpression:
FATAL_RUNTIME_ERROR_NO_LINE()
<< "Can't treat expression as lvalue: " << *exp;
}
}
// State transitions for expressions.
Transition StepExp() {
Ptr<Action> act = state->stack.Top()->todo.Top();
const Expression* exp = cast<ExpressionAction>(*act).Exp();
if (tracing_output) {
llvm::outs() << "--- step exp " << *exp << " --->\n";
}
switch (exp->Tag()) {
case Expression::Kind::IndexExpression: {
if (act->Pos() == 0) {
// { { e[i] :: C, E, F} :: S, H}
// -> { { e :: [][i] :: C, E, F} :: S, H}
return Spawn{global_arena->New<ExpressionAction>(
cast<IndexExpression>(*exp).Aggregate())};
} else if (act->Pos() == 1) {
return Spawn{global_arena->New<ExpressionAction>(
cast<IndexExpression>(*exp).Offset())};
} else {
// { { v :: [][i] :: C, E, F} :: S, H}
// -> { { v_i :: C, E, F} : S, H}
auto* tuple = dyn_cast<TupleValue>(act->Results()[0]);
if (tuple == nullptr) {
FATAL_RUNTIME_ERROR_NO_LINE()
<< "expected a tuple in field access, not " << *tuple;
}
std::string f =
std::to_string(cast<IntValue>(*act->Results()[1]).Val());
const Value* field = tuple->FindField(f);
if (field == nullptr) {
FATAL_RUNTIME_ERROR_NO_LINE()
<< "field " << f << " not in " << *tuple;
}
return Done{field};
}
}
case Expression::Kind::TupleLiteral: {
if (act->Pos() == 0) {
if (cast<TupleLiteral>(*exp).Fields().size() > 0) {
// { {(f1=e1,...) :: C, E, F} :: S, H}
// -> { {e1 :: (f1=[],...) :: C, E, F} :: S, H}
const Expression* e1 =
cast<TupleLiteral>(*exp).Fields()[0].expression;
return Spawn{global_arena->New<ExpressionAction>(e1)};
} else {
return Done{CreateTuple(act, exp)};
}
} else if (act->Pos() !=
static_cast<int>(cast<TupleLiteral>(*exp).Fields().size())) {
// { { vk :: (f1=v1,..., fk=[],fk+1=ek+1,...) :: C, E, F} :: S,
// H}
// -> { { ek+1 :: (f1=v1,..., fk=vk, fk+1=[],...) :: C, E, F} :: S,
// H}
const Expression* elt =
cast<TupleLiteral>(*exp).Fields()[act->Pos()].expression;
return Spawn{global_arena->New<ExpressionAction>(elt)};
} else {
return Done{CreateTuple(act, exp)};
}
}
case Expression::Kind::FieldAccessExpression: {
const auto& access = cast<FieldAccessExpression>(*exp);
if (act->Pos() == 0) {
// { { e.f :: C, E, F} :: S, H}
// -> { { e :: [].f :: C, E, F} :: S, H}
return Spawn{global_arena->New<ExpressionAction>(access.Aggregate())};
} else {
// { { v :: [].f :: C, E, F} :: S, H}
// -> { { v_f :: C, E, F} : S, H}
return Done{act->Results()[0]->GetField(FieldPath(access.Field()),
exp->LineNumber())};
}
}
case Expression::Kind::IdentifierExpression: {
CHECK(act->Pos() == 0);
const auto& ident = cast<IdentifierExpression>(*exp);
// { {x :: C, E, F} :: S, H} -> { {H(E(x)) :: C, E, F} :: S, H}
Address pointer = GetFromEnv(exp->LineNumber(), ident.Name());
return Done{state->heap.Read(pointer, exp->LineNumber())};
}
case Expression::Kind::IntLiteral:
CHECK(act->Pos() == 0);
// { {n :: C, E, F} :: S, H} -> { {n' :: C, E, F} :: S, H}
return Done{global_arena->RawNew<IntValue>(cast<IntLiteral>(*exp).Val())};
case Expression::Kind::BoolLiteral:
CHECK(act->Pos() == 0);
// { {n :: C, E, F} :: S, H} -> { {n' :: C, E, F} :: S, H}
return Done{
global_arena->RawNew<BoolValue>(cast<BoolLiteral>(*exp).Val())};
case Expression::Kind::PrimitiveOperatorExpression: {
const auto& op = cast<PrimitiveOperatorExpression>(*exp);
if (act->Pos() != static_cast<int>(op.Arguments().size())) {
// { {v :: op(vs,[],e,es) :: C, E, F} :: S, H}
// -> { {e :: op(vs,v,[],es) :: C, E, F} :: S, H}
const Expression* arg = op.Arguments()[act->Pos()];
return Spawn{global_arena->New<ExpressionAction>(arg)};
} else {
// { {v :: op(vs,[]) :: C, E, F} :: S, H}
// -> { {eval_prim(op, (vs,v)) :: C, E, F} :: S, H}
return Done{EvalPrim(op.Op(), act->Results(), exp->LineNumber())};
}
}
case Expression::Kind::CallExpression:
if (act->Pos() == 0) {
// { {e1(e2) :: C, E, F} :: S, H}
// -> { {e1 :: [](e2) :: C, E, F} :: S, H}
return Spawn{global_arena->New<ExpressionAction>(
cast<CallExpression>(*exp).Function())};
} else if (act->Pos() == 1) {
// { { v :: [](e) :: C, E, F} :: S, H}
// -> { { e :: v([]) :: C, E, F} :: S, H}
return Spawn{global_arena->New<ExpressionAction>(
cast<CallExpression>(*exp).Argument())};
} else if (act->Pos() == 2) {
// { { v2 :: v1([]) :: C, E, F} :: S, H}
// -> { {C',E',F'} :: {C, E, F} :: S, H}
switch (act->Results()[0]->Tag()) {
case Value::Kind::ClassType: {
const Value* arg = CopyVal(act->Results()[1], exp->LineNumber());
return Done{
global_arena->RawNew<StructValue>(act->Results()[0], arg)};
}
case Value::Kind::AlternativeConstructorValue: {
const auto& alt =
cast<AlternativeConstructorValue>(*act->Results()[0]);
const Value* arg = CopyVal(act->Results()[1], exp->LineNumber());
return Done{global_arena->RawNew<AlternativeValue>(
alt.AltName(), alt.ChoiceName(), arg)};
}
case Value::Kind::FunctionValue:
return CallFunction{
.function = cast<FunctionValue>(act->Results()[0]),
.args = act->Results()[1],
.line_num = exp->LineNumber()};
default:
FATAL_RUNTIME_ERROR(exp->LineNumber())
<< "in call, expected a function, not " << *act->Results()[0];
}
} else {
FATAL() << "in handle_value with Call pos " << act->Pos();
}
case Expression::Kind::IntrinsicExpression:
CHECK(act->Pos() == 0);
// { {n :: C, E, F} :: S, H} -> { {n' :: C, E, F} :: S, H}
switch (cast<IntrinsicExpression>(*exp).Intrinsic()) {
case IntrinsicExpression::IntrinsicKind::Print:
Address pointer = GetFromEnv(exp->LineNumber(), "format_str");
const Value* pointee = state->heap.Read(pointer, exp->LineNumber());
CHECK(pointee->Tag() == Value::Kind::StringValue);
// TODO: This could eventually use something like llvm::formatv.
llvm::outs() << cast<StringValue>(*pointee).Val();
return Done{&TupleValue::Empty()};
}
case Expression::Kind::IntTypeLiteral: {
CHECK(act->Pos() == 0);
return Done{global_arena->RawNew<IntType>()};
}
case Expression::Kind::BoolTypeLiteral: {
CHECK(act->Pos() == 0);
return Done{global_arena->RawNew<BoolType>()};
}
case Expression::Kind::TypeTypeLiteral: {
CHECK(act->Pos() == 0);
return Done{global_arena->RawNew<TypeType>()};
}
case Expression::Kind::FunctionTypeLiteral: {
if (act->Pos() == 0) {
return Spawn{global_arena->New<ExpressionAction>(
cast<FunctionTypeLiteral>(*exp).Parameter())};
} else if (act->Pos() == 1) {
// { { pt :: fn [] -> e :: C, E, F} :: S, H}
// -> { { e :: fn pt -> []) :: C, E, F} :: S, H}
return Spawn{global_arena->New<ExpressionAction>(
cast<FunctionTypeLiteral>(*exp).ReturnType())};
} else {
// { { rt :: fn pt -> [] :: C, E, F} :: S, H}
// -> { fn pt -> rt :: {C, E, F} :: S, H}
return Done{global_arena->RawNew<FunctionType>(
std::vector<GenericBinding>(), act->Results()[0],
act->Results()[1])};
}
}
case Expression::Kind::ContinuationTypeLiteral: {
CHECK(act->Pos() == 0);
return Done{global_arena->RawNew<ContinuationType>()};
}
case Expression::Kind::StringLiteral:
CHECK(act->Pos() == 0);
// { {n :: C, E, F} :: S, H} -> { {n' :: C, E, F} :: S, H}
return Done{
global_arena->RawNew<StringValue>(cast<StringLiteral>(*exp).Val())};
case Expression::Kind::StringTypeLiteral: {
CHECK(act->Pos() == 0);
return Done{global_arena->RawNew<StringType>()};
}
} // switch (exp->Tag)
}
Transition StepPattern() {
Ptr<Action> act = state->stack.Top()->todo.Top();
const Pattern* pattern = cast<PatternAction>(*act).Pat();
if (tracing_output) {
llvm::outs() << "--- step pattern " << *pattern << " --->\n";
}
switch (pattern->Tag()) {
case Pattern::Kind::AutoPattern: {
CHECK(act->Pos() == 0);
return Done{global_arena->RawNew<AutoType>()};
}
case Pattern::Kind::BindingPattern: {
const auto& binding = cast<BindingPattern>(*pattern);
if (act->Pos() == 0) {
return Spawn{global_arena->New<PatternAction>(binding.Type())};
} else {
return Done{global_arena->RawNew<BindingPlaceholderValue>(
binding.Name(), act->Results()[0])};
}
}
case Pattern::Kind::TuplePattern: {
const auto& tuple = cast<TuplePattern>(*pattern);
if (act->Pos() == 0) {
if (tuple.Fields().empty()) {
return Done{&TupleValue::Empty()};
} else {
const Pattern* p1 = tuple.Fields()[0].pattern;
return Spawn{(global_arena->New<PatternAction>(p1))};
}
} else if (act->Pos() != static_cast<int>(tuple.Fields().size())) {
// { { vk :: (f1=v1,..., fk=[],fk+1=ek+1,...) :: C, E, F} :: S,
// H}
// -> { { ek+1 :: (f1=v1,..., fk=vk, fk+1=[],...) :: C, E, F} :: S,
// H}
const Pattern* elt = tuple.Fields()[act->Pos()].pattern;
return Spawn{global_arena->New<PatternAction>(elt)};
} else {
std::vector<TupleElement> elements;
for (size_t i = 0; i < tuple.Fields().size(); ++i) {
elements.push_back(
{.name = tuple.Fields()[i].name, .value = act->Results()[i]});
}
return Done{global_arena->RawNew<TupleValue>(std::move(elements))};
}
}
case Pattern::Kind::AlternativePattern: {
const auto& alternative = cast<AlternativePattern>(*pattern);
if (act->Pos() == 0) {
return Spawn{
global_arena->New<ExpressionAction>(alternative.ChoiceType())};
} else if (act->Pos() == 1) {
return Spawn{global_arena->New<PatternAction>(alternative.Arguments())};
} else {
CHECK(act->Pos() == 2);
const auto& choice_type = cast<ChoiceType>(*act->Results()[0]);
return Done{global_arena->RawNew<AlternativeValue>(
alternative.AlternativeName(), choice_type.Name(),
act->Results()[1])};
}
}
case Pattern::Kind::ExpressionPattern:
return Delegate{global_arena->New<ExpressionAction>(
cast<ExpressionPattern>(pattern)->Expression())};
}
}
auto IsWhileAct(Ptr<Action> act) -> bool {
switch (act->Tag()) {
case Action::Kind::StatementAction:
switch (cast<StatementAction>(*act).Stmt()->Tag()) {
case Statement::Kind::While:
return true;
default:
return false;
}
default:
return false;
}
}
auto IsBlockAct(Ptr<Action> act) -> bool {
switch (act->Tag()) {
case Action::Kind::StatementAction:
switch (cast<StatementAction>(*act).Stmt()->Tag()) {
case Statement::Kind::Block:
return true;
default:
return false;
}
default:
return false;
}
}
// State transitions for statements.
Transition StepStmt() {
Ptr<Frame> frame = state->stack.Top();
Ptr<Action> act = frame->todo.Top();
const Statement* stmt = cast<StatementAction>(*act).Stmt();
CHECK(stmt != nullptr) << "null statement!";
if (tracing_output) {
llvm::outs() << "--- step stmt ";
stmt->PrintDepth(1, llvm::outs());
llvm::outs() << " --->\n";
}
switch (stmt->Tag()) {
case Statement::Kind::Match:
if (act->Pos() == 0) {
// { { (match (e) ...) :: C, E, F} :: S, H}
// -> { { e :: (match ([]) ...) :: C, E, F} :: S, H}
return Spawn{
global_arena->New<ExpressionAction>(cast<Match>(*stmt).Exp())};
} else {
// Regarding act->Pos():
// * odd: start interpreting the pattern of a clause
// * even: finished interpreting the pattern, now try to match
//
// Regarding act->Results():
// * 0: the value that we're matching
// * 1: the pattern for clause 0
// * 2: the pattern for clause 1
// * ...
auto clause_num = (act->Pos() - 1) / 2;
if (clause_num >=
static_cast<int>(cast<Match>(*stmt).Clauses()->size())) {
return Done{};
}
auto c = cast<Match>(*stmt).Clauses()->begin();
std::advance(c, clause_num);
if (act->Pos() % 2 == 1) {
// start interpreting the pattern of the clause
// { {v :: (match ([]) ...) :: C, E, F} :: S, H}
// -> { {pi :: (match ([]) ...) :: C, E, F} :: S, H}
return Spawn{global_arena->New<PatternAction>(c->first)};
} else { // try to match
auto v = act->Results()[0];
auto pat = act->Results()[clause_num + 1];
std::optional<Env> matches = PatternMatch(pat, v, stmt->LineNumber());
if (matches) { // we have a match, start the body
Env values = CurrentEnv(state);
std::list<std::string> vars;
for (const auto& [name, value] : *matches) {
values.Set(name, value);
vars.push_back(name);
}
frame->scopes.Push(global_arena->New<Scope>(values, vars));
const Statement* body_block =
global_arena->RawNew<Block>(stmt->LineNumber(), c->second);
auto body_act = global_arena->New<StatementAction>(body_block);
body_act->IncrementPos();
frame->todo.Pop(1);
frame->todo.Push(body_act);
frame->todo.Push(global_arena->New<StatementAction>(c->second));
return ManualTransition{};
} else {
// this case did not match, moving on
int next_clause_num = act->Pos() / 2;
if (next_clause_num ==
static_cast<int>(cast<Match>(*stmt).Clauses()->size())) {
return Done{};
}
return RunAgain{};
}
}
}
case Statement::Kind::While:
if (act->Pos() % 2 == 0) {
// { { (while (e) s) :: C, E, F} :: S, H}
// -> { { e :: (while ([]) s) :: C, E, F} :: S, H}
act->Clear();
return Spawn{
global_arena->New<ExpressionAction>(cast<While>(*stmt).Cond())};
} else if (cast<BoolValue>(*act->Results().back()).Val()) {
// { {true :: (while ([]) s) :: C, E, F} :: S, H}
// -> { { s :: (while (e) s) :: C, E, F } :: S, H}
return Spawn{
global_arena->New<StatementAction>(cast<While>(*stmt).Body())};
} else {
// { {false :: (while ([]) s) :: C, E, F} :: S, H}
// -> { { C, E, F } :: S, H}
return Done{};
}
case Statement::Kind::Break: {
CHECK(act->Pos() == 0);
// { { break; :: ... :: (while (e) s) :: C, E, F} :: S, H}
// -> { { C, E', F} :: S, H}
auto it =
std::find_if(frame->todo.begin(), frame->todo.end(), &IsWhileAct);
if (it == frame->todo.end()) {
FATAL_RUNTIME_ERROR(stmt->LineNumber())
<< "`break` not inside `while` statement";
}
++it;
return UnwindTo{*it};
}
case Statement::Kind::Continue: {
CHECK(act->Pos() == 0);
// { { continue; :: ... :: (while (e) s) :: C, E, F} :: S, H}
// -> { { (while (e) s) :: C, E', F} :: S, H}
auto it =
std::find_if(frame->todo.begin(), frame->todo.end(), &IsWhileAct);
if (it == frame->todo.end()) {
FATAL_RUNTIME_ERROR(stmt->LineNumber())
<< "`continue` not inside `while` statement";
}
return UnwindTo{*it};
}
case Statement::Kind::Block: {
if (act->Pos() == 0) {
const Block& block = cast<Block>(*stmt);
if (block.Stmt() != nullptr) {
frame->scopes.Push(global_arena->New<Scope>(CurrentEnv(state)));
return Spawn{global_arena->New<StatementAction>(block.Stmt())};
} else {
return Done{};
}
} else {
Ptr<Scope> scope = frame->scopes.Top();
DeallocateScope(scope);
frame->scopes.Pop(1);
return Done{};
}
}
case Statement::Kind::VariableDefinition:
if (act->Pos() == 0) {
// { {(var x = e) :: C, E, F} :: S, H}
// -> { {e :: (var x = []) :: C, E, F} :: S, H}
return Spawn{global_arena->New<ExpressionAction>(
cast<VariableDefinition>(*stmt).Init())};
} else if (act->Pos() == 1) {
return Spawn{global_arena->New<PatternAction>(
cast<VariableDefinition>(*stmt).Pat())};
} else {
// { { v :: (x = []) :: C, E, F} :: S, H}
// -> { { C, E(x := a), F} :: S, H(a := copy(v))}
const Value* v = act->Results()[0];
const Value* p = act->Results()[1];
std::optional<Env> matches = PatternMatch(p, v, stmt->LineNumber());
CHECK(matches)
<< stmt->LineNumber()
<< ": internal error in variable definition, match failed";
for (const auto& [name, value] : *matches) {
frame->scopes.Top()->values.Set(name, value);
frame->scopes.Top()->locals.push_back(name);
}
return Done{};
}
case Statement::Kind::ExpressionStatement:
if (act->Pos() == 0) {
// { {e :: C, E, F} :: S, H}
// -> { {e :: C, E, F} :: S, H}
return Spawn{global_arena->New<ExpressionAction>(
cast<ExpressionStatement>(*stmt).Exp())};
} else {
return Done{};
}
case Statement::Kind::Assign:
if (act->Pos() == 0) {
// { {(lv = e) :: C, E, F} :: S, H}
// -> { {lv :: ([] = e) :: C, E, F} :: S, H}
return Spawn{global_arena->New<LValAction>(cast<Assign>(*stmt).Lhs())};
} else if (act->Pos() == 1) {
// { { a :: ([] = e) :: C, E, F} :: S, H}
// -> { { e :: (a = []) :: C, E, F} :: S, H}
return Spawn{
global_arena->New<ExpressionAction>(cast<Assign>(*stmt).Rhs())};
} else {
// { { v :: (a = []) :: C, E, F} :: S, H}
// -> { { C, E, F} :: S, H(a := v)}
auto pat = act->Results()[0];
auto val = act->Results()[1];
PatternAssignment(pat, val, stmt->LineNumber());
return Done{};
}
case Statement::Kind::If:
if (act->Pos() == 0) {
// { {(if (e) then_stmt else else_stmt) :: C, E, F} :: S, H}
// -> { { e :: (if ([]) then_stmt else else_stmt) :: C, E, F} :: S, H}
return Spawn{
global_arena->New<ExpressionAction>(cast<If>(*stmt).Cond())};
} else if (cast<BoolValue>(*act->Results()[0]).Val()) {
// { {true :: if ([]) then_stmt else else_stmt :: C, E, F} ::
// S, H}
// -> { { then_stmt :: C, E, F } :: S, H}
return Delegate{
global_arena->New<StatementAction>(cast<If>(*stmt).ThenStmt())};
} else if (cast<If>(*stmt).ElseStmt()) {
// { {false :: if ([]) then_stmt else else_stmt :: C, E, F} ::
// S, H}
// -> { { else_stmt :: C, E, F } :: S, H}
return Delegate{
global_arena->New<StatementAction>(cast<If>(*stmt).ElseStmt())};
} else {
return Done{};
}
case Statement::Kind::Return:
if (act->Pos() == 0) {
// { {return e :: C, E, F} :: S, H}
// -> { {e :: return [] :: C, E, F} :: S, H}
return Spawn{
global_arena->New<ExpressionAction>(cast<Return>(*stmt).Exp())};
} else {
// { {v :: return [] :: C, E, F} :: {C', E', F'} :: S, H}
// -> { {v :: C', E', F'} :: S, H}
const Value* ret_val = CopyVal(act->Results()[0], stmt->LineNumber());
return UnwindFunctionCall{ret_val};
}
case Statement::Kind::Sequence: {
// { { (s1,s2) :: C, E, F} :: S, H}
// -> { { s1 :: s2 :: C, E, F} :: S, H}
const Sequence& seq = cast<Sequence>(*stmt);
if (act->Pos() == 0) {
return Spawn{global_arena->New<StatementAction>(seq.Stmt())};
} else {
if (seq.Next() != nullptr) {
return Delegate{
global_arena->New<StatementAction>(cast<Sequence>(*stmt).Next())};
} else {
return Done{};
}
}
}
case Statement::Kind::Continuation: {
CHECK(act->Pos() == 0);
// Create a continuation object by creating a frame similar the
// way one is created in a function call.
auto scopes =
Stack<Ptr<Scope>>(global_arena->New<Scope>(CurrentEnv(state)));
Stack<Ptr<Action>> todo;
todo.Push(global_arena->New<StatementAction>(
global_arena->RawNew<Return>(stmt->LineNumber(), nullptr,
/*is_omitted_exp=*/true)));
todo.Push(
global_arena->New<StatementAction>(cast<Continuation>(*stmt).Body()));
auto continuation_frame =
global_arena->New<Frame>("__continuation", scopes, todo);
Address continuation_address =
state->heap.AllocateValue(global_arena->RawNew<ContinuationValue>(
std::vector<Ptr<Frame>>({continuation_frame})));
// Store the continuation's address in the frame.
continuation_frame->continuation = continuation_address;
// Bind the continuation object to the continuation variable
frame->scopes.Top()->values.Set(
cast<Continuation>(*stmt).ContinuationVariable(),
continuation_address);
// Pop the continuation statement.
frame->todo.Pop();
return ManualTransition{};
}
case Statement::Kind::Run:
if (act->Pos() == 0) {
// Evaluate the argument of the run statement.
return Spawn{
global_arena->New<ExpressionAction>(cast<Run>(*stmt).Argument())};
} else {
frame->todo.Pop(1);
// Push an expression statement action to ignore the result
// value from the continuation.
auto ignore_result = global_arena->New<StatementAction>(
global_arena->RawNew<ExpressionStatement>(
stmt->LineNumber(),
global_arena->RawNew<TupleLiteral>(stmt->LineNumber())));
frame->todo.Push(ignore_result);
// Push the continuation onto the current stack.
const std::vector<Ptr<Frame>>& continuation_vector =
cast<ContinuationValue>(*act->Results()[0]).Stack();
for (auto frame_iter = continuation_vector.rbegin();
frame_iter != continuation_vector.rend(); ++frame_iter) {
state->stack.Push(*frame_iter);
}
return ManualTransition{};
}
case Statement::Kind::Await:
CHECK(act->Pos() == 0);
// Pause the current continuation
frame->todo.Pop();
std::vector<Ptr<Frame>> paused;
do {
paused.push_back(state->stack.Pop());
} while (paused.back()->continuation == std::nullopt);
// Update the continuation with the paused stack.
state->heap.Write(*paused.back()->continuation,
global_arena->RawNew<ContinuationValue>(paused),
stmt->LineNumber());
return ManualTransition{};
}
}
// Visitor which implements the behavior associated with each transition type.
struct DoTransition {
void operator()(const Done& done) {
Ptr<Frame> frame = state->stack.Top();
if (frame->todo.Top()->Tag() != Action::Kind::StatementAction) {
CHECK(done.result != nullptr);
frame->todo.Pop();
if (frame->todo.IsEmpty()) {
state->program_value = done.result;
} else {
frame->todo.Top()->AddResult(done.result);
}
} else {
CHECK(done.result == nullptr);
frame->todo.Pop();
}
}
void operator()(const Spawn& spawn) {
Ptr<Frame> frame = state->stack.Top();
frame->todo.Top()->IncrementPos();
frame->todo.Push(spawn.child);
}
void operator()(const Delegate& delegate) {
Ptr<Frame> frame = state->stack.Top();
frame->todo.Pop();
frame->todo.Push(delegate.delegate);
}
void operator()(const RunAgain&) {
state->stack.Top()->todo.Top()->IncrementPos();
}
void operator()(const UnwindTo& unwind_to) {
Ptr<Frame> frame = state->stack.Top();
// TODO: drop .Get() calls once `Ptr` has comparison operators
while (frame->todo.Top().Get() != unwind_to.new_top.Get()) {
if (IsBlockAct(frame->todo.Top())) {
DeallocateScope(frame->scopes.Top());
frame->scopes.Pop();
}
frame->todo.Pop();
}
}
void operator()(const UnwindFunctionCall& unwind) {
DeallocateLocals(state->stack.Top());
state->stack.Pop();
if (state->stack.Top()->todo.IsEmpty()) {
state->program_value = unwind.return_val;
} else {
state->stack.Top()->todo.Top()->AddResult(unwind.return_val);
}
}
void operator()(const CallFunction& call) {
state->stack.Top()->todo.Pop();
std::optional<Env> matches =
PatternMatch(call.function->Param(), call.args, call.line_num);
CHECK(matches.has_value())
<< "internal error in call_function, pattern match failed";
// Create the new frame and push it on the stack
Env values = globals;
std::list<std::string> params;
for (const auto& [name, value] : *matches) {
values.Set(name, value);
params.push_back(name);
}
auto scopes = Stack<Ptr<Scope>>(global_arena->New<Scope>(values, params));
auto todo = Stack<Ptr<Action>>(
global_arena->New<StatementAction>(call.function->Body()));
auto frame = global_arena->New<Frame>(call.function->Name(), scopes, todo);
state->stack.Push(frame);
}
void operator()(const ManualTransition&) {}
};
// State transition.
void Step() {
Ptr<Frame> frame = state->stack.Top();
if (frame->todo.IsEmpty()) {
FATAL_RUNTIME_ERROR_NO_LINE()
<< "fell off end of function " << frame->name << " without `return`";
}
Ptr<Action> act = frame->todo.Top();
switch (act->Tag()) {
case Action::Kind::LValAction:
std::visit(DoTransition(), StepLvalue());
break;
case Action::Kind::ExpressionAction:
std::visit(DoTransition(), StepExp());
break;
case Action::Kind::PatternAction:
std::visit(DoTransition(), StepPattern());
break;
case Action::Kind::StatementAction:
std::visit(DoTransition(), StepStmt());
break;
} // switch
}
// Interpret the whole porogram.
auto InterpProgram(const std::list<Ptr<const Declaration>>& fs) -> int {
state = global_arena->RawNew<State>(); // Runtime state.
if (tracing_output) {
llvm::outs() << "********** initializing globals **********\n";
}
InitGlobals(fs);
const Expression* arg = global_arena->RawNew<TupleLiteral>(0);
const Expression* call_main = global_arena->RawNew<CallExpression>(
0, global_arena->RawNew<IdentifierExpression>(0, "main"), arg);
auto todo =
Stack<Ptr<Action>>(global_arena->New<ExpressionAction>(call_main));
auto scopes = Stack<Ptr<Scope>>(global_arena->New<Scope>(globals));
state->stack =
Stack<Ptr<Frame>>(global_arena->New<Frame>("top", scopes, todo));
if (tracing_output) {
llvm::outs() << "********** calling main function **********\n";
PrintState(llvm::outs());
}
while (state->stack.Count() > 1 || !state->stack.Top()->todo.IsEmpty()) {
Step();
if (tracing_output) {
PrintState(llvm::outs());
}
}
return cast<IntValue>(**state->program_value).Val();
}
// Interpret an expression at compile-time.
auto InterpExp(Env values, const Expression* e) -> const Value* {
CHECK(state->program_value == std::nullopt);
auto program_value_guard =
llvm::make_scope_exit([] { state->program_value = std::nullopt; });
auto todo = Stack<Ptr<Action>>(global_arena->New<ExpressionAction>(e));
auto scopes = Stack<Ptr<Scope>>(global_arena->New<Scope>(values));
state->stack =
Stack<Ptr<Frame>>(global_arena->New<Frame>("InterpExp", scopes, todo));
while (state->stack.Count() > 1 || !state->stack.Top()->todo.IsEmpty()) {
Step();
}
CHECK(state->program_value != std::nullopt);
return *state->program_value;
}
// Interpret a pattern at compile-time.
auto InterpPattern(Env values, const Pattern* p) -> const Value* {
CHECK(state->program_value == std::nullopt);
auto program_value_guard =
llvm::make_scope_exit([] { state->program_value = std::nullopt; });
auto todo = Stack<Ptr<Action>>(global_arena->New<PatternAction>(p));
auto scopes = Stack<Ptr<Scope>>(global_arena->New<Scope>(values));
state->stack = Stack<Ptr<Frame>>(
global_arena->New<Frame>("InterpPattern", scopes, todo));
while (state->stack.Count() > 1 || !state->stack.Top()->todo.IsEmpty()) {
Step();
}
CHECK(state->program_value != std::nullopt);
return *state->program_value;
}
} // namespace Carbon
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