case *EmptyStmt: // nothing to do

	case *LabeledStmt:
		w.node(n.Label)
		w.node(n.Stmt)

	case *BlockStmt:
		w.stmtList(n.List)

	case *ExprStmt:
		w.node(n.X)

	case *SendStmt:
		w.node(n.Chan)
		w.node(n.Value)

	case *DeclStmt:
		w.declList(n.DeclList)

	case *AssignStmt:
		w.node(n.Lhs)
		if n.Rhs != nil {
			w.node(n.Rhs)
		}

	case *BranchStmt:

		Label *Name
		Stmt  Stmt
		stmt
	}

	BlockStmt struct {
		List   []Stmt
		Rbrace Pos
		stmt
	}

	ExprStmt struct {
		X Expr
		simpleStmt
	}

	SendStmt struct {
		Chan, Value Expr // Chan <- Value
		simpleStmt
	}

	DeclStmt struct {
		DeclList []Decl
		stmt
	}

	AssignStmt struct {
		Op       Operator // 0 means no operation

	case *DeclStmt:
		Walk(v, n.Decl)

	case *EmptyStmt:
		// nothing to do

	case *LabeledStmt:
		Walk(v, n.Label)
		Walk(v, n.Stmt)

	case *ExprStmt:
		Walk(v, n.X)

	case *SendStmt:
		Walk(v, n.Chan)
		Walk(v, n.Value)

	case *IncDecStmt:
		Walk(v, n.X)

	case *AssignStmt:
		walkList(v, n.Lhs)
		walkList(v, n.Rhs)

	case *GoStmt:
		Walk(v, n.Call)

	{"BlockStmt", `@{}`},

	// The position of an ExprStmt is the position of the expression.
	{"ExprStmt", `@<-ch`},
	{"ExprStmt", `f@()`},
	{"ExprStmt", `append@(s, 1, 2, 3)`},

	{"SendStmt", `ch @<- x`},

	{"DeclStmt", `@const x = 0`},
	{"DeclStmt", `@const (x = 0)`},
	{"DeclStmt", `@type T int`},
	{"DeclStmt", `@type T = int`},
	{"DeclStmt", `@type (T1 = int; T2 = float32)`},

		for i, clause := range s.Body {
			if clause == nil {
				continue // error reported before
			}

			// clause.Comm must be a SendStmt, RecvStmt, or default case
			valid := false
			var rhs syntax.Expr // rhs of RecvStmt, or nil
			switch s := clause.Comm.(type) {
			case nil, *syntax.SendStmt:
				valid = true
			case *syntax.AssignStmt:
				if _, ok := s.Rhs.(*syntax.ListExpr); !ok {
					rhs = s.Rhs
				}

			clause, _ := s.(*ast.CommClause)
			if clause == nil {
				continue // error reported before
			}

			// clause.Comm must be a SendStmt, RecvStmt, or default case
			valid := false
			var rhs ast.Expr // rhs of RecvStmt, or nil
			switch s := clause.Comm.(type) {
			case nil, *ast.SendStmt:
				valid = true
			case *ast.AssignStmt:
				if len(s.Rhs) == 1 {
					rhs = s.Rhs[0]
				}
			case *ast.ExprStmt:

	// within the body of switch/typeswitch/select/for/range.
	// It is effectively an additional default-nil parameter of stmt().
	var label *lblock
start:
	switch s := _s.(type) {
	case *ast.BadStmt,
		*ast.SendStmt,
		*ast.IncDecStmt,
		*ast.GoStmt,
		*ast.DeferStmt,
		*ast.EmptyStmt,
		*ast.AssignStmt:
		// No effect on control flow.
		b.add(s)

	case *ast.ExprStmt:
		b.add(s)

	case *ast.DeclStmt:
		f.walk(n.Decl, ctxDecl, visit)
	case *ast.EmptyStmt:
	case *ast.LabeledStmt:
		f.walk(n.Stmt, ctxStmt, visit)
	case *ast.ExprStmt:
		f.walk(&n.X, ctxExpr, visit)
	case *ast.SendStmt:
		f.walk(&n.Chan, ctxExpr, visit)
		f.walk(&n.Value, ctxExpr, visit)
	case *ast.IncDecStmt:
		f.walk(&n.X, ctxExpr, visit)
	case *ast.AssignStmt:
		f.walk(n.Lhs, ctxExpr, visit)

		// nothing to do

	case *ast.LabeledStmt:
		a.apply(n, "Label", nil, n.Label)
		a.apply(n, "Stmt", nil, n.Stmt)

	case *ast.ExprStmt:
		a.apply(n, "X", nil, n.X)

	case *ast.SendStmt:
		a.apply(n, "Chan", nil, n.Chan)
		a.apply(n, "Value", nil, n.Value)

	case *ast.IncDecStmt:
		a.apply(n, "X", nil, n.X)

	case *ast.AssignStmt:
		a.applyList(n, "Lhs")
		a.applyList(n, "Rhs")

	if p.tok == token.CASE {
		p.next()
		lhs := p.parseLhsList()
		if p.tok == token.ARROW {
			// SendStmt
			if len(lhs) > 1 {
				p.errorExpected(lhs[0].Pos(), "1 expression")
				// continue with first expression
			}
			arrow := p.pos
			p.next()
			rhs := p.parseRhs()
			comm = &ast.SendStmt{lhs[0], arrow, rhs}
		} else {
			// RecvStmt
			pos := p.pos
			tok := p.tok