func (s *state) evalFieldChain(dot, receiver reflect.Value, node parse.Node, ident []string, args []parse.Node, final reflect.Value) reflect.Value {
	n := len(ident)
	for i := 0; i < n-1; i++ {
		receiver = s.evalField(dot, ident[i], node, nil, zero, receiver)
	}
	return s.evalField(dot, ident[n-1], node, args, final, receiver)
}
evalFieldChain evaluates .X.Y.Z possibly followed by arguments.
dot is the environment in which to evaluate arguments, while
receiver is the value being walked along the chain.
package template
import (
	"bytes"
	"fmt"
	"io"
	"reflect"
	"runtime"
	"sort"
	"strings"
	"github.com/alecthomas/template/parse"
)
type state struct {
	tmpl *Template
	wr   io.Writer
	node parse.Node  
	vars []variable  
}
type variable struct {
	name  string
	value reflect.Value
}
func (s *state) push(name string, value reflect.Value) {
	s.vars = append(s.vars, variable{name, value})
}
func (s *state) mark() int {
	return len(s.vars)
}
func (s *state) pop(mark int) {
	s.vars = s.vars[0:mark]
}
func (s *state) setVar(n int, value reflect.Value) {
	s.vars[len(s.vars)-n].value = value
}
func (s *state) varValue(name string) reflect.Value {
	for i := s.mark() - 1; i >= 0; i-- {
		if s.vars[i].name == name {
			return s.vars[i].value
		}
	}
	s.errorf("undefined variable: %s", name)
	return zero
}
var zero reflect.Value
func (s *state) at(node parse.Node) {
	s.node = node
}
func doublePercent(str string) string {
	if strings.Contains(str, "%") {
		str = strings.Replace(str, "%", "%%", -1)
	}
	return str
}
func (s *state) errorf(format string, args ...interface{}) {
	name := doublePercent(s.tmpl.Name())
	if s.node == nil {
		format = fmt.Sprintf("template: %s: %s", name, format)
	} else {
		location, context := s.tmpl.ErrorContext(s.node)
		format = fmt.Sprintf("template: %s: executing %q at <%s>: %s", location, name, doublePercent(context), format)
	}
	panic(fmt.Errorf(format, args...))
}
func errRecover(errp *error) {
	e := recover()
	if e != nil {
		switch err := e.(type) {
		case runtime.Error:
			panic(e)
		case error:
			*errp = err
		default:
			panic(e)
		}
	}
}
func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{}) error {
	tmpl := t.tmpl[name]
	if tmpl == nil {
		return fmt.Errorf("template: no template %q associated with template %q", name, t.name)
	}
	return tmpl.Execute(wr, data)
}
func (t *Template) Execute(wr io.Writer, data interface{}) (err error) {
	defer errRecover(&err)
	value := reflect.ValueOf(data)
	state := &state{
		tmpl: t,
		wr:   wr,
		vars: []variable{{"$", value}},
	}
	t.init()
	if t.Tree == nil || t.Root == nil {
		var b bytes.Buffer
		for name, tmpl := range t.tmpl {
			if tmpl.Tree == nil || tmpl.Root == nil {
				continue
			}
			if b.Len() > 0 {
				b.WriteString(", ")
			}
			fmt.Fprintf(&b, "%q", name)
		}
		var s string
		if b.Len() > 0 {
			s = "; defined templates are: " + b.String()
		}
		state.errorf("%q is an incomplete or empty template%s", t.Name(), s)
	}
	state.walk(value, t.Root)
	return
}
func (s *state) walk(dot reflect.Value, node parse.Node) {
	s.at(node)
	switch node := node.(type) {
	case *parse.ActionNode:
		val := s.evalPipeline(dot, node.Pipe)
		if len(node.Pipe.Decl) == 0 {
			s.printValue(node, val)
		}
	case *parse.IfNode:
		s.walkIfOrWith(parse.NodeIf, dot, node.Pipe, node.List, node.ElseList)
	case *parse.ListNode:
		for _, node := range node.Nodes {
			s.walk(dot, node)
		}
	case *parse.RangeNode:
		s.walkRange(dot, node)
	case *parse.TemplateNode:
		s.walkTemplate(dot, node)
	case *parse.TextNode:
		if _, err := s.wr.Write(node.Text); err != nil {
			s.errorf("%s", err)
		}
	case *parse.WithNode:
		s.walkIfOrWith(parse.NodeWith, dot, node.Pipe, node.List, node.ElseList)
	default:
		s.errorf("unknown node: %s", node)
	}
}
func (s *state) walkIfOrWith(typ parse.NodeType, dot reflect.Value, pipe *parse.PipeNode, list, elseList *parse.ListNode) {
	defer s.pop(s.mark())
	val := s.evalPipeline(dot, pipe)
	truth, ok := isTrue(val)
	if !ok {
		s.errorf("if/with can't use %v", val)
	}
	if truth {
		if typ == parse.NodeWith {
			s.walk(val, list)
		} else {
			s.walk(dot, list)
		}
	} else if elseList != nil {
		s.walk(dot, elseList)
	}
}
func isTrue(val reflect.Value) (truth, ok bool) {
	if !val.IsValid() {
		return false, true
	}
	switch val.Kind() {
	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
		truth = val.Len() > 0
	case reflect.Bool:
		truth = val.Bool()
	case reflect.Complex64, reflect.Complex128:
		truth = val.Complex() != 0
	case reflect.Chan, reflect.Func, reflect.Ptr, reflect.Interface:
		truth = !val.IsNil()
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		truth = val.Int() != 0
	case reflect.Float32, reflect.Float64:
		truth = val.Float() != 0
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		truth = val.Uint() != 0
	case reflect.Struct:
		truth = true  
	default:
		return
	}
	return truth, true
}
func (s *state) walkRange(dot reflect.Value, r *parse.RangeNode) {
	s.at(r)
	defer s.pop(s.mark())
	val, _ := indirect(s.evalPipeline(dot, r.Pipe))
	mark := s.mark()
	oneIteration := func(index, elem reflect.Value) {
		if len(r.Pipe.Decl) > 0 {
			s.setVar(1, elem)
		}
		if len(r.Pipe.Decl) > 1 {
			s.setVar(2, index)
		}
		s.walk(elem, r.List)
		s.pop(mark)
	}
	switch val.Kind() {
	case reflect.Array, reflect.Slice:
		if val.Len() == 0 {
			break
		}
		for i := 0; i < val.Len(); i++ {
			oneIteration(reflect.ValueOf(i), val.Index(i))
		}
		return
	case reflect.Map:
		if val.Len() == 0 {
			break
		}
		for _, key := range sortKeys(val.MapKeys()) {
			oneIteration(key, val.MapIndex(key))
		}
		return
	case reflect.Chan:
		if val.IsNil() {
			break
		}
		i := 0
		for ; ; i++ {
			elem, ok := val.Recv()
			if !ok {
				break
			}
			oneIteration(reflect.ValueOf(i), elem)
		}
		if i == 0 {
			break
		}
		return
	case reflect.Invalid:
		break  
	default:
		s.errorf("range can't iterate over %v", val)
	}
	if r.ElseList != nil {
		s.walk(dot, r.ElseList)
	}
}
func (s *state) walkTemplate(dot reflect.Value, t *parse.TemplateNode) {
	s.at(t)
	tmpl := s.tmpl.tmpl[t.Name]
	if tmpl == nil {
		s.errorf("template %q not defined", t.Name)
	}
	dot = s.evalPipeline(dot, t.Pipe)
	newState := *s
	newState.tmpl = tmpl
	newState.vars = []variable{{"$", dot}}
	newState.walk(dot, tmpl.Root)
}
func (s *state) evalPipeline(dot reflect.Value, pipe *parse.PipeNode) (value reflect.Value) {
	if pipe == nil {
		return
	}
	s.at(pipe)
	for _, cmd := range pipe.Cmds {
		value = s.evalCommand(dot, cmd, value)  
		if value.Kind() == reflect.Interface && value.Type().NumMethod() == 0 {
			value = reflect.ValueOf(value.Interface())  
		}
	}
	for _, variable := range pipe.Decl {
		s.push(variable.Ident[0], value)
	}
	return value
}
func (s *state) notAFunction(args []parse.Node, final reflect.Value) {
	if len(args) > 1 || final.IsValid() {
		s.errorf("can't give argument to non-function %s", args[0])
	}
}
func (s *state) evalCommand(dot reflect.Value, cmd *parse.CommandNode, final reflect.Value) reflect.Value {
	firstWord := cmd.Args[0]
	switch n := firstWord.(type) {
	case *parse.FieldNode:
		return s.evalFieldNode(dot, n, cmd.Args, final)
	case *parse.ChainNode:
		return s.evalChainNode(dot, n, cmd.Args, final)
	case *parse.IdentifierNode:
		return s.evalFunction(dot, n, cmd, cmd.Args, final)
	case *parse.PipeNode:
		return s.evalPipeline(dot, n)
	case *parse.VariableNode:
		return s.evalVariableNode(dot, n, cmd.Args, final)
	}
	s.at(firstWord)
	s.notAFunction(cmd.Args, final)
	switch word := firstWord.(type) {
	case *parse.BoolNode:
		return reflect.ValueOf(word.True)
	case *parse.DotNode:
		return dot
	case *parse.NilNode:
		s.errorf("nil is not a command")
	case *parse.NumberNode:
		return s.idealConstant(word)
	case *parse.StringNode:
		return reflect.ValueOf(word.Text)
	}
	s.errorf("can't evaluate command %q", firstWord)
	panic("not reached")
}
func (s *state) idealConstant(constant *parse.NumberNode) reflect.Value {
	s.at(constant)
	switch {
	case constant.IsComplex:
		return reflect.ValueOf(constant.Complex128)  
	case constant.IsFloat && !isHexConstant(constant.Text) && strings.IndexAny(constant.Text, ".eE") >= 0:
		return reflect.ValueOf(constant.Float64)
	case constant.IsInt:
		n := int(constant.Int64)
		if int64(n) != constant.Int64 {
			s.errorf("%s overflows int", constant.Text)
		}
		return reflect.ValueOf(n)
	case constant.IsUint:
		s.errorf("%s overflows int", constant.Text)
	}
	return zero
}
func isHexConstant(s string) bool {
	return len(s) > 2 && s[0] == '0' && (s[1] == 'x' || s[1] == 'X')
}
func (s *state) evalFieldNode(dot reflect.Value, field *parse.FieldNode, args []parse.Node, final reflect.Value) reflect.Value {
	s.at(field)
	return s.evalFieldChain(dot, dot, field, field.Ident, args, final)
}
func (s *state) evalChainNode(dot reflect.Value, chain *parse.ChainNode, args []parse.Node, final reflect.Value) reflect.Value {
	s.at(chain)
	pipe := s.evalArg(dot, nil, chain.Node)
	if len(chain.Field) == 0 {
		s.errorf("internal error: no fields in evalChainNode")
	}
	return s.evalFieldChain(dot, pipe, chain, chain.Field, args, final)
}
func (s *state) evalVariableNode(dot reflect.Value, variable *parse.VariableNode, args []parse.Node, final reflect.Value) reflect.Value {
	s.at(variable)
	value := s.varValue(variable.Ident[0])
	if len(variable.Ident) == 1 {
		s.notAFunction(args, final)
		return value
	}
	return s.evalFieldChain(dot, value, variable, variable.Ident[1:], args, final)
}