// TODO determine a better range for BadExpr below
		par.List = []*ast.Field{{Type: &ast.BadExpr{pos, pos}}}
		return par
	}

	// recv type must be of the form ["*"] identifier
	recv := par.List[0]
	base := deref(recv.Type)
	if _, isIdent := base.(*ast.Ident); !isIdent {
		p.errorExpected(base.Pos(), "(unqualified) identifier")
		par.List = []*ast.Field{{Type: &ast.BadExpr{recv.Pos(), recv.End()}}}
	}

			return MakePos(n.Pos().Base(), 1, 1)

		// declarations
		// case *ImportDecl:
		// case *ConstDecl:
		// case *TypeDecl:
		// case *VarDecl:
		// case *FuncDecl:

		// expressions
		// case *BadExpr:
		// case *Name:
		// case *BasicLit:
		case *CompositeLit:
			if n.Type != nil {
				m = n.Type
				continue
			}
			return n.Pos()
		case *KeyValueExpr:
			m = n.Key
		// case *FuncLit:

					}
				}
			} else {
				msg = "mixed named and unnamed parameters"
			}
			p.syntaxErrorAt(errPos, msg)
		}
	}

	return
}

func (p *parser) badExpr() *BadExpr {
	b := new(BadExpr)
	b.pos = p.pos()
	return b
}

// ----------------------------------------------------------------------------
// Statements

			if index[1] == nil {
				p.error(colons[0], "middle index required in 3-index slice")
				index[1] = &ast.BadExpr{From: colons[0] + 1, To: colons[1]}
			}
			if index[2] == nil {
				p.error(colons[1], "final index required in 3-index slice")
				index[2] = &ast.BadExpr{From: colons[1] + 1, To: rbrack}
			}
		}

	switch n.(type) {
	case *ast.ArrayType:
		return 1 << nArrayType
	case *ast.AssignStmt:
		return 1 << nAssignStmt
	case *ast.BadDecl:
		return 1 << nBadDecl
	case *ast.BadExpr:
		return 1 << nBadExpr
	case *ast.BadStmt:
		return 1 << nBadStmt
	case *ast.BasicLit:
		return 1 << nBasicLit
	case *ast.BinaryExpr:
		return 1 << nBinaryExpr
	case *ast.BlockStmt:

			Walk(v, n.Type)
		}
		if n.Tag != nil {
			Walk(v, n.Tag)
		}
		if n.Comment != nil {
			Walk(v, n.Comment)
		}

	case *FieldList:
		walkList(v, n.List)

	// Expressions
	case *BadExpr, *Ident, *BasicLit:
		// nothing to do

	case *Ellipsis:
		if n.Elt != nil {
			Walk(v, n.Elt)
		}

	case *FuncLit:
		Walk(v, n.Type)
		Walk(v, n.Body)

	case *CompositeLit:

	// operator precedences. (This assumes that the AST was
	// generated by a Go parser.)

	switch x := x.(type) {
	default:
		fmt.Fprintf(buf, "(ast: %T)", x) // nil, ast.BadExpr, ast.KeyValueExpr

	case *ast.Ident:
		buf.WriteString(x.Name)

	case *ast.Ellipsis:
		buf.WriteString("...")
		if x.Elt != nil {
			WriteExpr(buf, x.Elt)
		}

	case *ast.BasicLit:

}

// An expression is represented by a tree consisting of one
// or more of the following concrete expression nodes.
type (
	// A BadExpr node is a placeholder for an expression containing
	// syntax errors for which a correct expression node cannot be
	// created.
	//
	BadExpr struct {
		From, To token.Pos // position range of bad expression
	}

	// An Ident node represents an identifier.
	Ident struct {

	case *ast.UnaryExpr:
		children = append(children, tok(n.OpPos, len(n.Op.String())))

	case *ast.ValueSpec:
		// TODO(adonovan): ValueSpec.{Doc,Comment}?

	case *ast.BadDecl, *ast.BadExpr, *ast.BadStmt:
		// nop
	}

	// TODO(adonovan): opt: merge the logic of ast.Inspect() into
	// the switch above so we can make interleaved callbacks for

		if n.Recv != nil {
			w.node(n.Recv)
		}
		w.node(n.Name)
		w.fieldList(n.TParamList)
		w.node(n.Type)
		if n.Body != nil {
			w.node(n.Body)
		}

	// expressions
	case *BadExpr: // nothing to do
	case *Name: // nothing to do
	case *BasicLit: // nothing to do

	case *CompositeLit:
		if n.Type != nil {
			w.node(n.Type)
		}
		w.exprList(n.ElemList)

	case *KeyValueExpr: