func IncDecStmt(stmt ast.Stmt, info *analysis.Info) ast.Stmt {
	if s, ok := stmt.(*ast.IncDecStmt); ok {
		t := info.Types[s.X].Type
		if iExpr, isIExpr := s.X.(*ast.IndexExpr); isIExpr {
			switch u := info.Types[iExpr.X].Type.Underlying().(type) {
			case *types.Array:
				t = u.Elem()
			case *types.Slice:
				t = u.Elem()
			case *types.Map:
				t = u.Elem()
			}
		}

		tok := token.ADD_ASSIGN
		if s.Tok == token.DEC {
			tok = token.SUB_ASSIGN
		}

		one := &ast.BasicLit{Kind: token.INT}
		info.Types[one] = types.TypeAndValue{Type: t, Value: exact.MakeInt64(1)}

		return &ast.AssignStmt{
			Lhs: []ast.Expr{s.X},
			Tok: tok,
			Rhs: []ast.Expr{one},
		}
	}
	return stmt
}

func (c *funcContext) zeroValue(ty types.Type) ast.Expr {
	switch t := ty.Underlying().(type) {
	case *types.Basic:
		switch {
		case isBoolean(t):
			return c.newConst(ty, exact.MakeBool(false))
		case isNumeric(t):
			return c.newConst(ty, exact.MakeInt64(0))
		case isString(t):
			return c.newConst(ty, exact.MakeString(""))
		case t.Kind() == types.UnsafePointer:
			// fall through to "nil"
		case t.Kind() == types.UntypedNil:
			panic("Zero value for untyped nil.")
		default:
			panic(fmt.Sprintf("Unhandled basic type: %v\n", t))
		}
	case *types.Array, *types.Struct:
		return c.setType(&ast.CompositeLit{}, ty)
	case *types.Chan, *types.Interface, *types.Map, *types.Signature, *types.Slice, *types.Pointer:
		// fall through to "nil"
	default:
		panic(fmt.Sprintf("Unhandled type: %T\n", t))
	}
	id := c.newIdent("nil", ty)
	c.p.Uses[id] = nilObj
	return id
}

// zeroConst returns a new "zero" constant of the specified type,
// which must not be an array or struct type: the zero values of
// aggregates are well-defined but cannot be represented by Const.
//
func zeroConst(t types.Type) *Const {
	switch t := t.(type) {
	case *types.Basic:
		switch {
		case t.Info()&types.IsBoolean != 0:
			return NewConst(exact.MakeBool(false), t)
		case t.Info()&types.IsNumeric != 0:
			return NewConst(exact.MakeInt64(0), t)
		case t.Info()&types.IsString != 0:
			return NewConst(exact.MakeString(""), t)
		case t.Kind() == types.UnsafePointer:
			fallthrough
		case t.Kind() == types.UntypedNil:
			return nilConst(t)
		default:
			panic(fmt.Sprint("zeroConst for unexpected type:", t))
		}
	case *types.Pointer, *types.Slice, *types.Interface, *types.Chan, *types.Map, *types.Signature:
		return nilConst(t)
	case *types.Named:
		return NewConst(zeroConst(t.Underlying()).Value, t)
	case *types.Array, *types.Struct, *types.Tuple:
		panic(fmt.Sprint("zeroConst applied to aggregate:", t))
	}
	panic(fmt.Sprint("zeroConst: unexpected ", t))
}

// number = int_lit [ "p" int_lit ] .
//
func (p *parser) parseNumber() (typ *types.Basic, val exact.Value) {
	// mantissa
	mant := exact.MakeFromLiteral(p.parseInt(), token.INT)
	if mant == nil {
		panic("invalid mantissa")
	}

	if p.lit == "p" {
		// exponent (base 2)
		p.next()
		exp, err := strconv.ParseInt(p.parseInt(), 10, 0)
		if err != nil {
			p.error(err)
		}
		if exp < 0 {
			denom := exact.MakeInt64(1)
			denom = exact.Shift(denom, token.SHL, uint(-exp))
			typ = types.Typ[types.UntypedFloat]
			val = exact.BinaryOp(mant, token.QUO, denom)
			return
		}
		if exp > 0 {
			mant = exact.Shift(mant, token.SHL, uint(exp))
		}
		typ = types.Typ[types.UntypedFloat]
		val = mant
		return
	}

	typ = types.Typ[types.UntypedInt]
	val = mant
	return
}

func (p *importer) ufloat() exact.Value {
	exp := p.int()
	x := exact.MakeFromBytes(p.bytes())
	switch {
	case exp < 0:
		d := exact.Shift(exact.MakeInt64(1), token.SHL, uint(-exp))
		x = exact.BinaryOp(x, token.QUO, d)
	case exp > 0:
		x = exact.Shift(x, token.SHL, uint(exp))
	}
	return x
}

func (p *importer) fraction() exact.Value {
	sign := p.int()
	if sign == 0 {
		return exact.MakeInt64(0)
	}

	x := exact.BinaryOp(p.ufloat(), token.QUO, p.ufloat())
	if sign < 0 {
		x = exact.UnaryOp(token.SUB, x, 0)
	}
	return x
}

func (p *importer) value() exact.Value {
	switch kind := exact.Kind(p.int()); kind {
	case falseTag:
		return exact.MakeBool(false)
	case trueTag:
		return exact.MakeBool(true)
	case int64Tag:
		return exact.MakeInt64(p.int64())
	case floatTag:
		return p.float()
	case fractionTag:
		return p.fraction()
	case complexTag:
		re := p.fraction()
		im := p.fraction()
		return exact.BinaryOp(re, token.ADD, exact.MakeImag(im))
	case stringTag:
		return exact.MakeString(p.string())
	default:
		panic(fmt.Sprintf("unexpected value kind %d", kind))
	}
}

//.........这里部分代码省略.........
					Tok: token.DEFINE,
					Rhs: rhs,
				}, nil)
			}
		case token.TYPE:
			for _, spec := range decl.Specs {
				o := c.p.Defs[spec.(*ast.TypeSpec).Name].(*types.TypeName)
				c.p.typeNames = append(c.p.typeNames, o)
				c.p.objectNames[o] = c.newVariableWithLevel(o.Name(), true)
				c.p.dependencies[o] = true
			}
		case token.CONST:
			// skip, constants are inlined
		}

	case *ast.ExprStmt:
		expr := c.translateExpr(s.X)
		if expr != nil && expr.String() != "" {
			c.Printf("%s;", expr)
		}

	case *ast.LabeledStmt:
		label := c.p.Defs[s.Label].(*types.Label)
		if c.GotoLabel[label] {
			c.PrintCond(false, s.Label.Name+":", fmt.Sprintf("case %d:", c.labelCase(label)))
		}
		c.translateStmt(s.Stmt, label)

	case *ast.GoStmt:
		c.Printf("$go(%s, [%s]);", c.translateExpr(s.Call.Fun), strings.Join(c.translateArgs(c.p.Types[s.Call.Fun].Type.Underlying().(*types.Signature), s.Call.Args, s.Call.Ellipsis.IsValid(), false), ", "))

	case *ast.SendStmt:
		chanType := c.p.Types[s.Chan].Type.Underlying().(*types.Chan)
		call := &ast.CallExpr{
			Fun:  c.newIdent("$send", types.NewSignature(nil, types.NewTuple(types.NewVar(0, nil, "", chanType), types.NewVar(0, nil, "", chanType.Elem())), nil, false)),
			Args: []ast.Expr{s.Chan, s.Value},
		}
		c.Blocking[call] = true
		c.translateStmt(&ast.ExprStmt{X: call}, label)

	case *ast.SelectStmt:
		var channels []string
		var caseClauses []ast.Stmt
		flattened := false
		hasDefault := false
		for i, s := range s.Body.List {
			clause := s.(*ast.CommClause)
			switch comm := clause.Comm.(type) {
			case nil:
				channels = append(channels, "[]")
				hasDefault = true
			case *ast.ExprStmt:
				channels = append(channels, c.formatExpr("[%e]", astutil.RemoveParens(comm.X).(*ast.UnaryExpr).X).String())
			case *ast.AssignStmt:
				channels = append(channels, c.formatExpr("[%e]", astutil.RemoveParens(comm.Rhs[0]).(*ast.UnaryExpr).X).String())
			case *ast.SendStmt:
				channels = append(channels, c.formatExpr("[%e, %e]", comm.Chan, comm.Value).String())
			default:
				panic(fmt.Sprintf("unhandled: %T", comm))
			}
			indexLit := &ast.BasicLit{Kind: token.INT}
			c.p.Types[indexLit] = types.TypeAndValue{Type: types.Typ[types.Int], Value: exact.MakeInt64(int64(i))}
			caseClauses = append(caseClauses, &ast.CaseClause{
				List: []ast.Expr{indexLit},
				Body: clause.Body,
			})
			flattened = flattened || c.Flattened[clause]
		}

		selectCall := c.setType(&ast.CallExpr{
			Fun:  c.newIdent("$select", types.NewSignature(nil, types.NewTuple(types.NewVar(0, nil, "", types.NewInterface(nil, nil))), types.NewTuple(types.NewVar(0, nil, "", types.Typ[types.Int])), false)),
			Args: []ast.Expr{c.newIdent(fmt.Sprintf("[%s]", strings.Join(channels, ", ")), types.NewInterface(nil, nil))},
		}, types.Typ[types.Int])
		c.Blocking[selectCall] = !hasDefault
		selectionVar := c.newVariable("_selection")
		c.Printf("%s = %s;", selectionVar, c.translateExpr(selectCall))

		translateCond := func(cond ast.Expr) *expression {
			return c.formatExpr("%s[0] === %e", selectionVar, cond)
		}
		printCaseBodyPrefix := func(index int) {
			if assign, ok := s.Body.List[index].(*ast.CommClause).Comm.(*ast.AssignStmt); ok {
				switch rhsType := c.p.Types[assign.Rhs[0]].Type.(type) {
				case *types.Tuple:
					c.translateStmt(&ast.AssignStmt{Lhs: assign.Lhs, Rhs: []ast.Expr{c.newIdent(selectionVar+"[1]", rhsType)}, Tok: assign.Tok}, nil)
				default:
					c.translateStmt(&ast.AssignStmt{Lhs: assign.Lhs, Rhs: []ast.Expr{c.newIdent(selectionVar+"[1][0]", rhsType)}, Tok: assign.Tok}, nil)
				}
			}
		}
		c.translateBranchingStmt(caseClauses, true, translateCond, printCaseBodyPrefix, label, flattened)

	case *ast.EmptyStmt:
		// skip

	default:
		panic(fmt.Sprintf("Unhandled statement: %T\n", s))

	}
}

func (check *Checker) declStmt(decl ast.Decl) {
	pkg := check.pkg

	switch d := decl.(type) {
	case *ast.BadDecl:
		// ignore

	case *ast.GenDecl:
		var last *ast.ValueSpec // last ValueSpec with type or init exprs seen
		for iota, spec := range d.Specs {
			switch s := spec.(type) {
			case *ast.ValueSpec:
				switch d.Tok {
				case token.CONST:
					// determine which init exprs to use
					switch {
					case s.Type != nil || len(s.Values) > 0:
						last = s
					case last == nil:
						last = new(ast.ValueSpec) // make sure last exists
					}

					// declare all constants
					lhs := make([]*Const, len(s.Names))
					for i, name := range s.Names {
						obj := NewConst(name.Pos(), pkg, name.Name, nil, exact.MakeInt64(int64(iota)))
						lhs[i] = obj

						var init ast.Expr
						if i < len(last.Values) {
							init = last.Values[i]
						}

						check.constDecl(obj, last.Type, init)
					}

					check.arityMatch(s, last)

					// spec: "The scope of a constant or variable identifier declared
					// inside a function begins at the end of the ConstSpec or VarSpec
					// (ShortVarDecl for short variable declarations) and ends at the
					// end of the innermost containing block."
					scopePos := s.End()
					for i, name := range s.Names {
						check.declare(check.scope, name, lhs[i], scopePos)
					}

				case token.VAR:
					lhs0 := make([]*Var, len(s.Names))
					for i, name := range s.Names {
						lhs0[i] = NewVar(name.Pos(), pkg, name.Name, nil)
					}

					// initialize all variables
					for i, obj := range lhs0 {
						var lhs []*Var
						var init ast.Expr
						switch len(s.Values) {
						case len(s.Names):
							// lhs and rhs match
							init = s.Values[i]
						case 1:
							// rhs is expected to be a multi-valued expression
							lhs = lhs0
							init = s.Values[0]
						default:
							if i < len(s.Values) {
								init = s.Values[i]
							}
						}
						check.varDecl(obj, lhs, s.Type, init)
						if len(s.Values) == 1 {
							// If we have a single lhs variable we are done either way.
							// If we have a single rhs expression, it must be a multi-
							// valued expression, in which case handling the first lhs
							// variable will cause all lhs variables to have a type
							// assigned, and we are done as well.
							if debug {
								for _, obj := range lhs0 {
									assert(obj.typ != nil)
								}
							}
							break
						}
					}

					check.arityMatch(s, nil)

					// declare all variables
					// (only at this point are the variable scopes (parents) set)
					scopePos := s.End() // see constant declarations
					for i, name := range s.Names {
						// see constant declarations
						check.declare(check.scope, name, lhs0[i], scopePos)
					}

				default:
					check.invalidAST(s.Pos(), "invalid token %s", d.Tok)
				}

//.........这里部分代码省略.........

//.........这里部分代码省略.........
			// fallthrough
		}

		// check general case by creating custom signature
		sig := makeSig(S, S, NewSlice(T)) // []T required for variadic signature
		sig.variadic = true
		check.arguments(x, call, sig, func(x *operand, i int) {
			// only evaluate arguments that have not been evaluated before
			if i < len(alist) {
				*x = alist[i]
				return
			}
			arg(x, i)
		}, nargs)
		// ok to continue even if check.arguments reported errors

		x.mode = value
		x.typ = S
		if check.Types != nil {
			check.recordBuiltinType(call.Fun, sig)
		}

	case _Cap, _Len:
		// cap(x)
		// len(x)
		mode := invalid
		var typ Type
		var val exact.Value
		switch typ = implicitArrayDeref(x.typ.Underlying()); t := typ.(type) {
		case *Basic:
			if isString(t) && id == _Len {
				if x.mode == constant {
					mode = constant
					val = exact.MakeInt64(int64(len(exact.StringVal(x.val))))
				} else {
					mode = value
				}
			}

		case *Array:
			mode = value
			// spec: "The expressions len(s) and cap(s) are constants
			// if the type of s is an array or pointer to an array and
			// the expression s does not contain channel receives or
			// function calls; in this case s is not evaluated."
			if !check.hasCallOrRecv {
				mode = constant
				val = exact.MakeInt64(t.len)
			}

		case *Slice, *Chan:
			mode = value

		case *Map:
			if id == _Len {
				mode = value
			}
		}

		if mode == invalid {
			check.invalidArg(x.pos(), "%s for %s", x, bin.name)
			return
		}

		x.mode = mode
		x.typ = Typ[Int]

//.........这里部分代码省略.........
									// TODO(gri) When we import a package, we create
									// a new local package object. We should do the
									// same for each dot-imported object. That way
									// they can have correct position information.
									// (We must not modify their existing position
									// information because the same package - found
									// via Config.Packages - may be dot-imported in
									// another package!)
									check.declare(fileScope, nil, obj, token.NoPos)
									check.recordImplicit(s, obj)
								}
							}
							// add position to set of dot-import positions for this file
							// (this is only needed for "imported but not used" errors)
							check.addUnusedDotImport(fileScope, imp, s.Pos())
						} else {
							// declare imported package object in file scope
							check.declare(fileScope, nil, obj, token.NoPos)
						}

					case *ast.ValueSpec:
						switch d.Tok {
						case token.CONST:
							// determine which initialization expressions to use
							switch {
							case s.Type != nil || len(s.Values) > 0:
								last = s
							case last == nil:
								last = new(ast.ValueSpec) // make sure last exists
							}

							// declare all constants
							for i, name := range s.Names {
								obj := NewConst(name.Pos(), pkg, name.Name, nil, exact.MakeInt64(int64(iota)))

								var init ast.Expr
								if i < len(last.Values) {
									init = last.Values[i]
								}

								d := &declInfo{file: fileScope, typ: last.Type, init: init}
								check.declarePkgObj(name, obj, d)
							}

							check.arityMatch(s, last)

						case token.VAR:
							lhs := make([]*Var, len(s.Names))
							// If there's exactly one rhs initializer, use
							// the same declInfo d1 for all lhs variables
							// so that each lhs variable depends on the same
							// rhs initializer (n:1 var declaration).
							var d1 *declInfo
							if len(s.Values) == 1 {
								// The lhs elements are only set up after the for loop below,
								// but that's ok because declareVar only collects the declInfo
								// for a later phase.
								d1 = &declInfo{file: fileScope, lhs: lhs, typ: s.Type, init: s.Values[0]}
							}

							// declare all variables
							for i, name := range s.Names {
								obj := NewVar(name.Pos(), pkg, name.Name, nil)
								lhs[i] = obj

								d := d1

	res := NewVar(token.NoPos, nil, "", Typ[String])
	sig := &Signature{results: NewTuple(res)}
	err := NewFunc(token.NoPos, nil, "Error", sig)
	typ := &Named{underlying: NewInterface([]*Func{err}, nil).Complete()}
	sig.recv = NewVar(token.NoPos, nil, "", typ)
	def(NewTypeName(token.NoPos, nil, "error", typ))
}

var predeclaredConsts = [...]struct {
	name string
	kind BasicKind
	val  exact.Value
}{
	{"true", UntypedBool, exact.MakeBool(true)},
	{"false", UntypedBool, exact.MakeBool(false)},
	{"iota", UntypedInt, exact.MakeInt64(0)},
}

func defPredeclaredConsts() {
	for _, c := range predeclaredConsts {
		def(NewConst(token.NoPos, nil, c.name, Typ[c.kind], c.val))
	}
}

func defPredeclaredNil() {
	def(&Nil{object{name: "nil", typ: Typ[UntypedNil]}})
}

// A builtinId is the id of a builtin function.
type builtinId int

// intConst returns an 'int' constant that evaluates to i.
// (i is an int64 in case the host is narrower than the target.)
func intConst(i int64) *Const {
	return NewConst(exact.MakeInt64(i), tInt)
}