fix: call frame handling, logical short circuiting
This commit is contained in:
Brett Broadhurst
parent
5c133e5fa2
commit
236acc7d60
8 changed files with 301 additions and 159 deletions
165
src/Story.zig
165
src/Story.zig
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@ -100,10 +100,13 @@ pub const Opcode = enum(u8) {
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};
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pub const CallFrame = struct {
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/// Pointer to the knot that initiated the call.
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callee: *Object.Knot,
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caller_top: usize,
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/// Instruction pointer.
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ip: usize,
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sp: usize,
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bp: usize,
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/// Output stream base.
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output_base: usize,
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};
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pub const Value = union(enum) {
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@ -377,11 +380,11 @@ fn getConstant(story: *Story, frame: *CallFrame, offset: u8) !Value {
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}
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fn getLocal(vm: *Story, frame: *CallFrame, offset: u8) ?Value {
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return vm.stack[frame.sp + offset];
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return vm.stack[frame.bp + offset + 1];
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}
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fn setLocal(vm: *Story, frame: *CallFrame, offset: u8, value: Value) void {
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vm.stack[frame.sp + offset] = value;
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vm.stack[frame.bp + offset + 1] = value;
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}
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// TODO: This should probably check the constants table first.
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@ -426,68 +429,58 @@ pub fn getKnot(vm: *Story, name: []const u8) ?*Object.Knot {
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return knot;
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}
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fn call(vm: *Story, knot: *Object.Knot) !void {
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if (vm.call_stack_top >= vm.call_stack.len)
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return error.CallStackOverflow;
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const locals_count = knot.code.locals_count;
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const args_count = knot.code.args_count;
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const sp = vm.stack_top - args_count;
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const caller_top = if (vm.call_stack_top == 0)
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sp
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else
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sp - 1;
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const frame_top = sp + args_count + locals_count;
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if (frame_top > vm.stack.len) return error.StackOverflow;
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for (vm.stack[sp + args_count .. frame_top]) |*slot| slot.* = .nil;
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vm.stack_top = frame_top;
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vm.call_stack[vm.call_stack_top] = .{
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.callee = knot,
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.ip = 0,
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.sp = sp,
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.caller_top = caller_top,
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};
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vm.call_stack_top += 1;
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fn callValue(vm: *Story, value: Value, args_count: u8) !void {
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switch (value) {
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.object => |object| switch (object.tag) {
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.knot => return call(vm, @ptrCast(object), args_count),
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else => return error.InvalidCallTarget,
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},
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else => return error.InvalidCallTarget,
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}
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}
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// Diverts are essentially tail calls.
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fn divert(vm: *Story, knot: *Object.Knot) !void {
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const args_count = knot.code.args_count;
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const locals_count = knot.code.locals_count;
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fn call(vm: *Story, knot: *Object.Knot, args_count: u8) !void {
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assert(knot.code.args_count == args_count);
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if (vm.call_stack_top >= vm.call_stack.len)
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return error.CallStackOverflow;
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if (!vm.can_advance)
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vm.can_advance = true;
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if (vm.call_stack_top == 0)
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return vm.call(knot);
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const args_start = vm.stack_top - args_count;
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const current_frame = &vm.call_stack[vm.call_stack_top - 1];
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const sp = current_frame.sp;
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const caller_top = current_frame.caller_top;
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if (args_count > 0) {
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std.mem.copyForwards(
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Value,
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vm.stack[sp .. sp + args_count],
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vm.stack[args_start .. args_start + args_count],
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);
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}
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const frame_top = sp + args_count + locals_count;
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if (frame_top > vm.stack.len) return error.StackOverflow;
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for (vm.stack[sp + args_count .. frame_top]) |*slot| slot.* = .nil;
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vm.stack_top = frame_top;
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current_frame.* = .{
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vm.call_stack[vm.call_stack_top] = .{
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.callee = knot,
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.ip = 0,
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.sp = sp,
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.caller_top = caller_top,
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.bp = vm.stack_top - args_count - 1,
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.output_base = vm.output_buffer.items.len,
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};
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vm.call_stack_top += 1;
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vm.stack_top += knot.code.locals_count;
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}
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fn divertValue(vm: *Story, value: Value, args_count: u8) !void {
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switch (value) {
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.object => |object| switch (object.tag) {
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.knot => return divert(vm, @ptrCast(object), args_count),
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else => return error.InvalidCallTarget,
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},
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else => return error.InvalidCallTarget,
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}
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}
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// Diverts are essentially tail calls.
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fn divert(vm: *Story, knot: *Object.Knot, args_count: u8) !void {
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assert(knot.code.args_count == args_count);
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if (vm.call_stack_top == 0)
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return vm.call(knot, args_count);
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const frame = &vm.call_stack[vm.call_stack_top - 1];
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frame.* = .{
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.callee = knot,
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.ip = 0,
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.bp = vm.stack_top - args_count - 1,
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.output_base = vm.output_buffer.items.len,
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};
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vm.stack_top += knot.code.locals_count;
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}
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fn readAddress(code: []const Story.Opcode, offset: usize) u16 {
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@ -518,16 +511,32 @@ fn step(vm: *Story) !StepSignal {
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.exit => return .exit,
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.done => return .done,
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.ret => {
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const return_value = vm.stack[vm.stack_top - 1];
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if (vm.call_stack_top == 0) return error.UnexpectedReturn;
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vm.call_stack_top -= 1;
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const completed_frame = vm.call_stack[vm.call_stack_top];
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vm.stack_top = completed_frame.caller_top;
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const resolved_stream: ?Value = if (vm.output_buffer.items.len > frame.output_base) blk: {
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const frame_output = vm.output_buffer.items[frame.output_base..];
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defer vm.output_buffer.shrinkRetainingCapacity(frame.output_base);
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const str_bytes = try resolveOutputStream(vm, arena, frame_output);
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const str_object = try Object.String.create(vm, .{ .bytes = str_bytes });
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break :blk .{ .object = &str_object.base };
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} else blk: {
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break :blk null;
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};
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const return_value = if (resolved_stream) |stream| blk: {
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if (frame.bp + frame.callee.code.stack_size + 1 < vm.stack_top) {
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try vm.output_buffer.append(gpa, .{ .value = stream });
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break :blk popStack(vm).?;
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}
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break :blk stream;
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} else if (frame.bp + frame.callee.code.stack_size + 1 < vm.stack_top) blk: {
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break :blk popStack(vm).?;
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} else .nil;
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vm.stack_top = frame.bp;
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vm.stack[vm.stack_top] = return_value;
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vm.stack_top += 1;
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if (vm.call_stack_top == 0) return error.UnexpectedReturn;
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frame = &vm.call_stack[vm.call_stack_top - 1];
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},
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.pop => {
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@ -629,17 +638,11 @@ fn step(vm: *Story) !StepSignal {
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}
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},
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.call => {
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const arg_offset: u8 = @intFromEnum(code[frame.ip + 1]);
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const args_count: u8 = @intFromEnum(code[frame.ip + 1]);
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frame.ip += 2;
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if (peekStack(vm, arg_offset)) |value| {
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switch (value) {
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.object => |object| switch (object.tag) {
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.knot => try call(vm, @ptrCast(object)),
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else => unreachable,
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},
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else => unreachable,
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}
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if (peekStack(vm, args_count)) |value| {
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try callValue(vm, value, args_count);
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} else {
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return error.InvalidArgument;
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}
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@ -647,17 +650,11 @@ fn step(vm: *Story) !StepSignal {
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frame = &vm.call_stack[vm.call_stack_top - 1];
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},
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.divert => {
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const arg_offset: u8 = @intFromEnum(code[frame.ip + 1]);
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const args_count: u8 = @intFromEnum(code[frame.ip + 1]);
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frame.ip += 2;
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if (peekStack(vm, arg_offset)) |value| {
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switch (value) {
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.object => |object| switch (object.tag) {
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.knot => try divert(vm, @ptrCast(object)),
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else => unreachable,
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},
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else => unreachable,
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}
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if (peekStack(vm, args_count)) |value| {
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try divertValue(vm, value, args_count);
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} else {
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return error.InvalidArgument;
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}
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@ -831,6 +828,7 @@ pub fn advance(story: *Story) !?[]const u8 {
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}
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}
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story.can_advance = false;
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if (output_buffer.items.len == 0) return null;
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return try resolveOutputStream(story, arena, output_buffer.items[0..]);
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}
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@ -906,7 +904,8 @@ pub fn fromSourceBytes(
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try comp.setupStoryRuntime(gpa, &story);
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if (story.getKnot(Story.default_knot_name)) |knot| {
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try story.divert(knot);
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try story.pushStack(.{ .object = &knot.base });
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try story.divert(knot, 0);
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}
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return story;
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}
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