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vm.cpp
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/*
Copyright 2015 Google Inc. All rights reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
#include "vm.h"
#include <cassert>
#include <cmath>
#include <set>
#include <string>
#include "parser.h"
#include "state.h"
#include "static_analysis.h"
namespace {
/** Turn a path e.g. "/a/b/c" into a dir, e.g. "/a/b/". If there is no path returns "".
*/
std::string dir_name(const std::string &path)
{
size_t last_slash = path.rfind('/');
if (last_slash != std::string::npos) {
return path.substr(0, last_slash+1);
}
return "";
}
enum FrameKind {
FRAME_APPLY_TARGET,
FRAME_BINARY_LEFT,
FRAME_BINARY_RIGHT,
FRAME_BUILTIN_FILTER,
FRAME_BUILTIN_FORCE_THUNKS,
FRAME_CALL,
FRAME_ERROR,
FRAME_EQUALITY_MANIFEST,
FRAME_IF,
FRAME_INDEX_TARGET,
FRAME_INDEX_INDEX,
FRAME_LOCAL,
FRAME_OBJECT,
FRAME_OBJECT_COMP_ARRAY,
FRAME_OBJECT_COMP_ELEMENT,
FRAME_STRING_CONCAT,
FRAME_UNARY
};
/** A frame on the stack.
*
* Every time a subterm is evaluated, we first push a new stack frame to
* store the continuation.
*
* The stack frame is a bit like a tagged union, except not as memory
* efficient. The set of member variables that are actually used depends on
* the value of the member varaible kind.
*
* If the stack frame is of kind FRAME_CALL, then it counts towards the
* maximum number of stack frames allowed. Other stack frames are not
* counted. This is because FRAME_CALL exists where there is a branch in
* the code, e.g. the forcing of a thunk, evaluation of a field, calling a
* function, etc.
*
* The stack is used to mark objects during garbage
* collection, so HeapObjects not referred to from the stack may be
* prematurely collected.
*/
struct Frame {
/** Tag (tagged union). */
FrameKind kind;
/** The code we were executing before. */
const AST *ast;
/** The location of the code we were executing before.
*
* loc == ast->location when ast != nullptr
*/
LocationRange location;
/** Reuse this stack frame for the purpose of tail call optimization. */
bool tailCall;
/** Used for a variety of purposes. */
Value val;
/** Used for a variety of purposes. */
Value val2;
/** Used for a variety of purposes. */
Object::Fields::const_iterator fit;
/** Used for a variety of purposes. */
std::map<const Identifier *, HeapSimpleObject::Field> objectFields;
/** Used for a variety of purposes. */
unsigned elementId;
/** Used for a variety of purposes. */
std::map<const Identifier *, HeapThunk*> elements;
/** Used for a variety of purposes. */
std::vector<HeapThunk*> thunks;
/** The context is used in error messages to attempt to find a reasonable name for the
* object, function, or thunk value being executed.
*/
HeapEntity *context;
/** The lexically nearest object we are in, or nullptr. Note
* that this is not the same as context, because we could be inside a function,
* inside an object and then context would be the function, but self would still point
* to the object.
*/
HeapObject *self;
/** The "super" level of self. Sometimes, we look upwards in the
* inheritance tree, e.g. via an explicit use of super, or because a given field
* has been inherited. When evaluating a field from one of these super objects,
* we need to bind self to the concrete object (so self must point
* there) but uses of super should be resolved relative to the object whose
* field we are evaluating. Thus, we keep a second field for that. This is
* usually 0, unless we are evaluating a super object's field.
*/
unsigned offset;
/** A set of variables introduced at this point. */
BindingFrame bindings;
Frame(const FrameKind &kind, const AST *ast)
: kind(kind), ast(ast), location(ast->location), tailCall(false), elementId(0),
context(NULL), self(NULL), offset(0)
{
val.t = Value::NULL_TYPE;
val2.t = Value::NULL_TYPE;
}
Frame(const FrameKind &kind, const LocationRange &location)
: kind(kind), ast(nullptr), location(location), tailCall(false), elementId(0),
context(NULL), self(NULL), offset(0)
{
val.t = Value::NULL_TYPE;
val2.t = Value::NULL_TYPE;
}
/** Mark everything visible from this frame. */
void mark(Heap &heap) const
{
heap.markFrom(val);
heap.markFrom(val2);
if (context) heap.markFrom(context);
if (self) heap.markFrom(self);
for (const auto &bind : bindings)
heap.markFrom(bind.second);
for (const auto &el : elements)
heap.markFrom(el.second);
for (const auto &th : thunks)
heap.markFrom(th);
}
bool isCall(void) const
{
return kind == FRAME_CALL;
}
};
/** The stack holds all the stack frames and manages the stack frame limit. */
class Stack {
/** How many call frames are on the stack. */
unsigned calls;
/** How many call frames should be allowed before aborting the program. */
unsigned limit;
/** The stack frames. */
std::vector<Frame> stack;
public:
Stack(unsigned limit)
: calls(0), limit(limit)
{
}
~Stack(void) { }
unsigned size(void)
{
return stack.size();
}
/** Search for the closest variable in scope that matches the given name. */
HeapThunk *lookUpVar(const Identifier *id)
{
for (int i=stack.size()-1 ; i>=0 ; --i) {
const auto &binds = stack[i].bindings;
auto it = binds.find(id);
if (it != binds.end()) {
return it->second;
}
if (stack[i].isCall()) break;
}
return nullptr;
}
/** Mark everything visible from the stack (any frame). */
void mark(Heap &heap)
{
for (const auto &f : stack) {
f.mark(heap);
}
}
Frame &top(void)
{
return stack.back();
}
const Frame &top(void) const
{
return stack.back();
}
void pop(void)
{
if (top().isCall()) calls--;
stack.pop_back();
}
/** Attempt to find a name for a given heap entity. This may not be possible, but we try
* reasonably hard. We look in the bindings for a variable in the closest scope that
* happens to point at the entity in question. Otherwise, the best we can do is use its
* type.
*/
std::string getName(unsigned from_here, const HeapEntity *e)
{
std::string name;
for (int i=from_here-1 ; i>=0; --i) {
const auto &f = stack[i];
for (const auto &pair : f.bindings) {
HeapThunk *thunk = pair.second;
if (!thunk->filled) continue;
if (!thunk->content.isHeap()) continue;
if (e != thunk->content.v.h) continue;
name = pair.first->name;
}
// Do not go into the next call frame, keep local reasoning.
if (f.isCall()) break;
}
if (name == "") name = "anonymous";
if (dynamic_cast<const HeapObject*>(e)) {
return "object <" + name + ">";
} else if (auto *thunk = dynamic_cast<const HeapThunk*>(e)) {
return "thunk <" + thunk->name->name + ">";
} else {
const auto *func = static_cast<const HeapClosure *>(e);
if (func->body == nullptr) {
name = jsonnet_builtin_decl(func->builtin).name;
return "builtin function <" + name + ">";
}
return "function <" + name + ">";
}
}
/** Dump the stack.
*
* This is useful to help debug the VM in gdb. It is virtual to stop it
* being removed by the compiler.
*/
virtual void dump(void)
{
for (unsigned i=0 ; i<stack.size() ; ++i) {
std::cout << "stack[" << i << "] = " << stack[i].location
<< " (" << stack[i].kind << ")"
<< std::endl;
}
std::cout << std::endl;
}
/** Creates the error object for throwing, and also populates it with the stack trace.
*/
RuntimeError makeError(const LocationRange &loc, const std::string &msg)
{
std::vector<TraceFrame> stack_trace;
stack_trace.push_back(TraceFrame(loc));
for (int i=stack.size()-1 ; i>=0 ; --i) {
const auto &f = stack[i];
if (f.isCall()) {
if (f.context != nullptr) {
// Give the last line a name.
stack_trace[stack_trace.size()-1].name = getName(i, f.context);
}
stack_trace.push_back(TraceFrame(f.location));
}
}
return RuntimeError(stack_trace, msg);
}
/** New (non-call) frame. */
template <class... Args> void newFrame(Args... args)
{
stack.emplace_back(args...);
}
/** If there is a tailstrict annotated frame followed by some locals, pop them all. */
void tailCallTrimStack (void)
{
for (int i=stack.size()-1 ; i>=0 ; --i) {
switch (stack[i].kind) {
case FRAME_CALL: {
if (!stack[i].tailCall || stack[i].thunks.size() > 0) {
return;
}
// Remove all stack frames including this one.
while (stack.size() > unsigned(i)) stack.pop_back();
calls--;
return;
} break;
case FRAME_LOCAL: break;
default: return;
}
}
}
/** New call frame. */
void newCall(const LocationRange &loc, HeapEntity *context, HeapObject *self,
unsigned offset, const BindingFrame &up_values)
{
tailCallTrimStack();
if (calls >= limit) {
throw makeError(loc, "Max stack frames exceeded.");
}
stack.emplace_back(FRAME_CALL, loc);
calls++;
top().context = context;
top().self = self;
top().offset = offset;
top().bindings = up_values;
top().tailCall = false;
#ifndef NDEBUG
for (const auto &bind : up_values) {
assert(bind.second != nullptr);
}
#endif
}
/** Look up the stack to find the self binding. */
void getSelfBinding(HeapObject *&self, unsigned &offset)
{
self = nullptr;
offset = 0;
for (int i=stack.size() - 1 ; i>=0 ; --i) {
if (stack[i].isCall()) {
self = stack[i].self;
offset = stack[i].offset;
return;
}
}
}
};
/** Typedef to save some typing. */
typedef std::map<std::string, std::string> StrMap;
/** Holds the intermediate state during execution and implements the necessary functions to
* implement the semantics of the language.
*
* The garbage collector used is a simple stop-the-world mark and sweep collector. It runs upon
* memory allocation if the heap is large enough and has grown enough since the last collection.
* All reachable entities have their mark field incremented. Then all entities with the old
* mark are removed from the heap.
*/
class Interpreter {
/** The heap. */
Heap heap;
/** The value last computed. */
Value scratch;
/** The stack. */
Stack stack;
/** Used to create ASTs if needed.
*
* This is used at import time, and in a few other cases.
*/
Allocator *alloc;
/** Used to "name" thunks crated on the inside of an array. */
const Identifier *idArrayElement;
/** Cache for imported Jsonnet files. */
std::map<std::pair<std::string, std::string>, const std::string *> cachedImports;
/** External variables for std.extVar. */
StrMap externalVars;
/** The callback used for loading imported files. */
JsonnetImportCallback *importCallback;
/** User context pointer for the import callback. */
void *importCallbackContext;
RuntimeError makeError(const LocationRange &loc, const std::string &msg)
{
return stack.makeError(loc, msg);
}
/** Create an object on the heap, maybe collect garbage.
* \param T Something under HeapEntity
* \returns The new object
*/
template <class T, class... Args> T* makeHeap(Args... args)
{
T *r = heap.makeEntity<T, Args...>(args...);
if (heap.checkHeap()) { // Do a GC cycle?
// Avoid the object we just made being collected.
heap.markFrom(r);
// Mark from the stack.
stack.mark(heap);
// Mark from the scratch register
heap.markFrom(scratch);
// Delete unreachable objects.
heap.sweep();
}
return r;
}
Value makeBoolean(bool v)
{
Value r;
r.t = Value::BOOLEAN;
r.v.b = v;
return r;
}
Value makeDouble(double v)
{
Value r;
r.t = Value::DOUBLE;
r.v.d = v;
return r;
}
Value makeDoubleCheck(const LocationRange &loc, double v)
{
if (std::isnan(v)) {
throw makeError(loc, "Not a number");
}
if (std::isinf(v)) {
throw makeError(loc, "Overflow");
}
return makeDouble(v);
}
Value makeNull(void)
{
Value r;
r.t = Value::NULL_TYPE;
return r;
}
Value makeArray(const std::vector<HeapThunk*> &v)
{
Value r;
r.t = Value::ARRAY;
r.v.h = makeHeap<HeapArray>(v);
return r;
}
Value makeClosure(const BindingFrame &env,
HeapObject *self,
unsigned offset,
const std::vector<const Identifier *> ¶ms,
AST *body)
{
Value r;
r.t = Value::FUNCTION;
r.v.h = makeHeap<HeapClosure>(env, self, offset, params, body, 0);
return r;
}
Value makeBuiltin(unsigned long builtin_id, const std::vector<const Identifier *> ¶ms)
{
AST *body = nullptr;
Value r;
r.t = Value::FUNCTION;
r.v.h = makeHeap<HeapClosure>(BindingFrame(), nullptr, 0,
params, body, builtin_id);
return r;
}
template <class T, class... Args> Value makeObject(Args... args)
{
Value r;
r.t = Value::OBJECT;
r.v.h = makeHeap<T>(args...);
return r;
}
Value makeString(const std::string &v)
{
Value r;
r.t = Value::STRING;
r.v.h = makeHeap<HeapString>(v);
return r;
}
/** Auxiliary function of objectIndex.
*
* Traverse the object's tree from right to left, looking for an object
* with the given field. Call with offset initially set to 0.
*
* \param f The field we're looking for.
* \param curr The root object.
* \param start_from Step over this many leaves first.
* \param counter Return the level of "super" that contained the field.
* \param self Return the new root.
* \returns The first object with the field, or nullptr if it could not be found.
*/
HeapLeafObject *findObject(const Identifier *f, HeapObject *root, HeapObject *curr,
unsigned start_from, unsigned &counter,
HeapObject *&self)
{
if (auto *ext = dynamic_cast<HeapExtendedObject*>(curr)) {
auto *r = findObject(f, root, ext->right, start_from, counter, self);
if (r) return r;
auto *l = findObject(f, root, ext->left, start_from, counter, self);
if (l) return l;
} else if (auto *super = dynamic_cast<HeapSuperObject*>(curr)) {
unsigned counter2 = 0;
auto *needle = findObject(f, super->root, super->root, super->offset, counter2, self);
if (needle != nullptr) {
counter = counter2;
return needle;
}
} else {
if (counter >= start_from) {
if (auto *simp = dynamic_cast<HeapSimpleObject*>(curr)) {
auto it = simp->fields.find(f);
if (it != simp->fields.end()) {
self = root;
return simp;
}
} else if (auto *comp = dynamic_cast<HeapComprehensionObject*>(curr)) {
auto it = comp->compValues.find(f);
if (it != comp->compValues.end()) {
self = root;
return comp;
}
}
}
counter++;
}
return nullptr;
}
typedef std::map<const Identifier*, Object::Field::Hide> IdHideMap;
/** Auxiliary function.
*/
IdHideMap objectFields(const HeapObject *obj_,
unsigned &counter, unsigned skip,
bool manifesting)
{
IdHideMap r;
if (auto *obj = dynamic_cast<const HeapSimpleObject*>(obj_)) {
counter++;
if (counter <= skip) return r;
for (const auto &f : obj->fields) {
r[f.first] = !manifesting ? Object::Field::VISIBLE : f.second.hide;
}
} else if (auto *obj = dynamic_cast<const HeapExtendedObject*>(obj_)) {
r = objectFields(obj->right, counter, skip, manifesting);
for (const auto &pair : objectFields(obj->left, counter, skip, manifesting)) {
auto it = r.find(pair.first);
if (it == r.end()) {
// First time it is seen
r[pair.first] = pair.second;
} else if (it->second == Object::Field::INHERIT) {
// Seen before, but with inherited visibility so use new visibility
r[pair.first] = pair.second;
}
}
} else if (auto *obj = dynamic_cast<const HeapSuperObject*>(obj_)) {
unsigned counter2 = 0;
return objectFields(obj->root, counter2, obj->offset, manifesting);
} else if (auto *obj = dynamic_cast<const HeapComprehensionObject*>(obj_)) {
counter++;
if (counter <= skip) return r;
for (const auto &f : obj->compValues)
r[f.first] = Object::Field::VISIBLE;
}
return r;
}
/** Auxiliary function.
*/
std::set<const Identifier*> objectFields(const HeapObject *obj_, bool manifesting)
{
unsigned counter = 0;
std::set<const Identifier*> r;
for (const auto &pair : objectFields(obj_, counter, 0, manifesting)) {
if (pair.second != Object::Field::HIDDEN) r.insert(pair.first);
}
return r;
}
/** Import another Jsonnet file.
*
* If the file has already been imported, then use that version. This maintains
* referential transparency in the case of writes to disk during execution.
*
* \param loc Location of the import statement.
* \param file Path to the filename.
*/
AST *import(const LocationRange &loc, const std::string &file)
{
const std::string *input = importString(loc, file);
auto *expr = jsonnet_parse(alloc, file, input->c_str());
jsonnet_static_analysis(expr);
return expr;
}
/** Import a file as a string.
*
* If the file has already been imported, then use that version. This maintains
* referential transparency in the case of writes to disk during execution.
*
* \param loc Location of the import statement.
* \param file Path to the filename.
*/
const std::string *importString(const LocationRange &loc, const std::string &file)
{
std::string dir = dir_name(loc.file);
std::pair<std::string, std::string> key(dir, file);
const std::string *str = cachedImports[key];
if (str != nullptr) return str;
int success = 0;
char *content =
importCallback(importCallbackContext, dir.c_str(), file.c_str(), &success);
std::string input(content);
input.assign(content);
::free(content);
if (!success) {
std::string msg = "Couldn't open import \"" + file + "\": ";
msg += input;
throw makeError(loc, msg);
}
std::string *input_ptr = new std::string(input);
cachedImports[key] = input_ptr;
return input_ptr;
}
/** Capture the required variables from the environment. */
BindingFrame capture(const std::vector<const Identifier*> &free_vars)
{
BindingFrame env;
for (auto fv : free_vars) {
auto *th = stack.lookUpVar(fv);
if (th != nullptr) {
env[fv] = th;
}
}
return env;
}
/** Count the number of leaves in the tree.
*
* \param obj The root of the tree.
* \param counter Initialize to 0, returns the number of leaves.
*/
unsigned countLeaves(HeapObject *obj)
{
if (auto *ext = dynamic_cast<HeapExtendedObject*>(obj)) {
return countLeaves(ext->left) + countLeaves(ext->right);
} else if (auto *super = dynamic_cast<HeapSuperObject*>(obj)) {
return countLeaves(super->root);
} else {
return 1;
}
}
public:
/** Create a new interpreter.
*
* \param loc The location range of the file to be executed.
*/
Interpreter(Allocator *alloc, const StrMap &ext_vars,
unsigned max_stack, double gc_min_objects, double gc_growth_trigger,
JsonnetImportCallback *import_callback, void *import_callback_context)
: heap(gc_min_objects, gc_growth_trigger), stack(max_stack), alloc(alloc),
idArrayElement(alloc->makeIdentifier("array_element")), externalVars(ext_vars),
importCallback(import_callback), importCallbackContext(import_callback_context)
{
scratch = makeNull();
}
/** Clean up the heap, stack, stash, and builtin function ASTs. */
~Interpreter()
{
for (const auto &pair : cachedImports) {
delete pair.second;
}
}
const Value &getScratchRegister(void)
{
return scratch;
}
void setScratchRegister(const Value &v)
{
scratch = v;
}
/** Test two values for equality.
*
* When not in strong mode, this will evaluate object fields, so can trigger a garbage
* collection cycle. Be sure to stash any objects that aren't reachable via the stack or
* heap.
*/
bool equality(const LocationRange &loc, const Value &a, const Value &b)
{
if (a.t != b.t) return false;
switch (a.t) {
case Value::ARRAY: {
auto *arr_a = static_cast<HeapArray*>(a.v.h);
auto *arr_b = static_cast<HeapArray*>(b.v.h);
if (arr_a->elements.size() != arr_b->elements.size()) return false;
for (unsigned long i=0 ; i<arr_a->elements.size() ; ++i) {
auto th_a = arr_a->elements[i];
if (!th_a->filled) {
stack.newCall(loc, th_a, th_a->self, th_a->offset, th_a->upValues);
evaluate(th_a->body);
stack.pop();
th_a->fill(scratch);
}
auto th_b = arr_b->elements[i];
if (!th_b->filled) {
stack.newCall(loc, th_b, th_b->self, th_b->offset, th_b->upValues);
evaluate(th_b->body);
stack.pop();
th_b->fill(scratch);
}
if (!equality(loc, th_a->content, th_b->content))
return false;
}
return true;
}
case Value::BOOLEAN:
return a.v.b == b.v.b;
case Value::DOUBLE:
return a.v.d == b.v.d;
case Value::FUNCTION:
return false;
case Value::NULL_TYPE:
return true;
case Value::OBJECT: {
auto *obj_a = static_cast<HeapObject*>(a.v.h);
auto *obj_b = static_cast<HeapObject*>(b.v.h);
std::set<const Identifier *> fields_a = objectFields(obj_a, true);
std::set<const Identifier *> fields_b = objectFields(obj_b, true);
if (fields_a != fields_b) return false;
// Put the two intermediate values on the stack so they won't get garbage
// collected.
stack.newFrame(FRAME_EQUALITY_MANIFEST, loc);
bool different = false;
for (const auto &f : fields_a) {
const AST *body_a = objectIndex(loc, obj_a, f);
evaluate(body_a);
stack.pop();
stack.top().val = scratch;
const AST *body_b = objectIndex(loc, obj_b, f);
evaluate(body_b);
stack.pop();
stack.top().val2 = scratch;
if (!equality(loc, stack.top().val, stack.top().val2)) {
different = true;
break;
}
}
stack.pop();
return !different;
}
case Value::STRING: {
auto *str_a = static_cast<HeapString*>(a.v.h);
auto *str_b = static_cast<HeapString*>(b.v.h);
return str_a->value == str_b->value;
}
}
// Compiler thinks this is reachable, even though it is not.
return false;
}
/** Raise an error if the arguments aren't the expected types. */
void validateBuiltinArgs(const LocationRange &loc,
unsigned long builtin,
const std::vector<Value> &args,
const std::vector<Value::Type> params)
{
if (args.size() == params.size()) {
for (unsigned i=0 ; i<args.size() ; ++i) {
if (args[i].t != params[i]) goto bad;
}
return;
}
bad:;
const std::string &name = jsonnet_builtin_decl(builtin).name;
std::stringstream ss;
ss << "Builtin function " + name + " expected (";
const char *prefix = "";
for (auto p : params) {
ss << prefix << type_str(p);
prefix = ", ";
}
ss << ") but got (";
prefix = "";
for (auto a : args) {
ss << prefix << type_str(a);
prefix = ", ";
}
ss << ")";
throw makeError(loc, ss.str());
}
std::string toString(const LocationRange &loc)
{
return manifestJson(loc, false, "");
}
/** Index an object's field.
*
* \param loc Location where the e.f occured.
* \param obj The target
* \param f The field
*/
const AST *objectIndex(const LocationRange &loc, HeapObject *obj,
const Identifier *f)
{
unsigned found_at = 0;
HeapObject *self = nullptr;
HeapLeafObject *found = findObject(f, obj, obj, 0, found_at, self);
if (found == nullptr) {
throw makeError(loc, "Field does not exist: " + f->name);
}
if (auto *simp = dynamic_cast<HeapSimpleObject*>(found)) {
auto it = simp->fields.find(f);
const AST *body = it->second.body;
stack.newCall(loc, simp, self, found_at, simp->upValues);
return body;
} else {
// If a HeapLeafObject is not HeapSimpleObject, it must be HeapComprehensionObject.
auto *comp = static_cast<HeapComprehensionObject*>(found);
auto it = comp->compValues.find(f);
auto *th = it->second;
BindingFrame binds = comp->upValues;
binds[comp->id] = th;
stack.newCall(loc, comp, self, found_at, binds);
return comp->value;
}
}
/** Evaluate the given AST to a value.
*
* Rather than call itself recursively, this function maintains a separate stack of
* partially-evaluated constructs. First, the AST is handled depending on its type. If
* this cannot be completed without evaluating another AST (e.g. a sub expression) then a
* frame is pushed onto the stack containing the partial state, and the code jumps back to
* the beginning of this function. Once there are no more ASTs to evaluate, the code
* executes the second part of the function to unwind the stack. If the stack cannot be
* completely unwound without evaluating an AST then it jumps back to the beginning of the
* function again. The process terminates when the AST has been processed and the stack is
* the same size it was at the beginning of the call to evaluate.
*/
void evaluate(const AST *ast_)
{
unsigned initial_stack_size = stack.size();
recurse:
switch (ast_->type) {
case AST_APPLY: {
const auto &ast = *static_cast<const Apply*>(ast_);
stack.newFrame(FRAME_APPLY_TARGET, ast_);
ast_ = ast.target;
goto recurse;
} break;
case AST_ARRAY: {
const auto &ast = *static_cast<const Array*>(ast_);
HeapObject *self;
unsigned offset;
stack.getSelfBinding(self, offset);
scratch = makeArray({});
auto &elements = static_cast<HeapArray*>(scratch.v.h)->elements;
for (const AST *el : ast.elements) {
auto *el_th = makeHeap<HeapThunk>(idArrayElement, self, offset, el);
el_th->upValues = capture(el->freeVariables);
elements.push_back(el_th);
}
} break;
case AST_BINARY: {
const auto &ast = *static_cast<const Binary*>(ast_);
stack.newFrame(FRAME_BINARY_LEFT, ast_);
ast_ = ast.left;
goto recurse;
} break;
case AST_BUILTIN_FUNCTION: {
const auto &ast = *static_cast<const BuiltinFunction*>(ast_);
scratch = makeBuiltin(ast.id, ast.params);
} break;
case AST_CONDITIONAL: {
const auto &ast = *static_cast<const Conditional*>(ast_);
stack.newFrame(FRAME_IF, ast_);
ast_ = ast.cond;
goto recurse;
} break;
case AST_ERROR: {
const auto &ast = *static_cast<const Error*>(ast_);
stack.newFrame(FRAME_ERROR, ast_);
ast_ = ast.expr;
goto recurse;
} break;
case AST_FUNCTION: {
const auto &ast = *static_cast<const Function*>(ast_);
auto env = capture(ast.freeVariables);
HeapObject *self;
unsigned offset;
stack.getSelfBinding(self, offset);
scratch = makeClosure(env, self, offset, ast.parameters, ast.body);
} break;
case AST_IMPORT: {