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ast.go
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//
// Copyright (c) 2023-2024 Markku Rossi
//
// All rights reserved.
//
package scheme
import (
"fmt"
"github.com/markkurossi/scheme/types"
)
// AST defines an abstract syntax tree entry
type AST interface {
Locator() Locator
Equal(o AST) bool
Type(ctx types.Ctx) *types.Type
Typecheck(lib *Library, round int) error
Bytecode(lib *Library) error
}
var (
_ AST = &ASTSequence{}
_ AST = &ASTDefine{}
_ AST = &ASTSet{}
_ AST = &ASTLet{}
_ AST = &ASTIf{}
_ AST = &ASTApply{}
_ AST = &ASTCall{}
_ AST = &ASTCallUnary{}
_ AST = &ASTLambda{}
_ AST = &ASTConstant{}
_ AST = &ASTIdentifier{}
_ AST = &ASTCond{}
_ AST = &ASTCase{}
_ AST = &ASTAnd{}
_ AST = &ASTOr{}
_ AST = &ASTPragma{}
)
// ASTSequence implements a (begin ...) sequence.
type ASTSequence struct {
From Locator
Items []AST
}
// Add adds an item to the sequence.
func (ast *ASTSequence) Add(item AST) {
ast.Items = append(ast.Items, item)
}
// Locator implements AST.Locator.
func (ast *ASTSequence) Locator() Locator {
return ast.From
}
// Equal implements AST.Equal.
func (ast *ASTSequence) Equal(o AST) bool {
oast, ok := o.(*ASTSequence)
if !ok {
return false
}
if len(ast.Items) != len(oast.Items) {
return false
}
for idx, item := range ast.Items {
if !item.Equal(oast.Items[idx]) {
return false
}
}
return true
}
// Type implements AST.Type.
func (ast *ASTSequence) Type(ctx types.Ctx) *types.Type {
if len(ast.Items) == 0 {
return types.Unspecified
}
return ast.Items[len(ast.Items)-1].Type(ctx)
}
// Typecheck implements AST.Typecheck.
func (ast *ASTSequence) Typecheck(lib *Library, round int) error {
for _, item := range ast.Items {
err := item.Typecheck(lib, round)
if err != nil {
return err
}
}
return nil
}
// Bytecode implements AST.Bytecode.
func (ast *ASTSequence) Bytecode(lib *Library) error {
for _, item := range ast.Items {
err := item.Bytecode(lib)
if err != nil {
return err
}
}
return nil
}
// ASTDefine implements (define name value).
type ASTDefine struct {
From Locator
Name *Identifier
Flags Flags
Value AST
}
// Locator implements AST.Locator.
func (ast *ASTDefine) Locator() Locator {
return ast.From
}
// Equal implements AST.Equal.
func (ast *ASTDefine) Equal(o AST) bool {
oast, ok := o.(*ASTDefine)
if !ok {
return false
}
return ast.Name.Name == oast.Name.Name &&
ast.Flags == oast.Flags &&
ast.Value.Equal(oast.Value)
}
// Type implements AST.Type.
func (ast *ASTDefine) Type(ctx types.Ctx) *types.Type {
return ast.Value.Type(ctx)
}
// Typecheck implements AST.Typecheck.
func (ast *ASTDefine) Typecheck(lib *Library, round int) error {
err := ast.Value.Typecheck(lib, round)
if err != nil {
return err
}
sym := lib.scm.Intern(ast.Name.Name)
ctx := make(types.Ctx)
nt := ast.Value.Type(ctx)
if round == 0 {
if !sym.GlobalType.IsA(types.Unspecified) {
return ast.From.Errorf("redefining symbol '%s'", ast.Name.Name)
}
sym.GlobalType = nt
lib.recheck = true
} else {
if !nt.IsA(sym.GlobalType) {
sym.GlobalType = nt
lib.recheck = true
}
}
return nil
}
// Bytecode implements AST.Bytecode.
func (ast *ASTDefine) Bytecode(lib *Library) error {
err := ast.Value.Bytecode(lib)
if err != nil {
return err
}
return lib.define(ast.From, ast.Name, ast.Flags)
}
// ASTSet implements (set name value).
type ASTSet struct {
From Locator
Name string
Binding *EnvBinding
Value AST
}
// Locator implements AST.Locator.
func (ast *ASTSet) Locator() Locator {
return ast.From
}
// Equal implements AST.Equal.
func (ast *ASTSet) Equal(o AST) bool {
oast, ok := o.(*ASTSet)
if !ok {
return false
}
if ast.Binding == nil && oast.Binding != nil {
return false
}
if ast.Binding != nil && oast.Binding == nil {
return false
}
return ast.Name == oast.Name && ast.Value.Equal(oast.Value)
}
// Type implements AST.Type.
func (ast *ASTSet) Type(ctx types.Ctx) *types.Type {
return ast.Value.Type(ctx)
}
// Typecheck implements AST.Typecheck.
func (ast *ASTSet) Typecheck(lib *Library, round int) error {
ctx := make(types.Ctx)
vtype := ast.Value.Type(ctx)
if ast.Binding != nil {
// let-variables can be assigned with different value types.
return nil
}
sym := lib.scm.Intern(ast.Name)
if sym.GlobalType.IsA(types.Unspecified) {
return ast.From.Errorf("setting undefined symbol '%s'", ast.Name)
}
if !vtype.IsKindOf(sym.GlobalType) {
return ast.From.Errorf("can't assign %s to variable of type %s",
vtype, sym.GlobalType)
}
return nil
}
// Bytecode implements AST.Bytecode.
func (ast *ASTSet) Bytecode(lib *Library) error {
err := ast.Value.Bytecode(lib)
if err != nil {
return err
}
if ast.Binding != nil {
lib.setBinding(ast.From, ast.Binding)
} else {
instr := lib.addInstr(ast.From, OpGlobalSet, nil, 0)
instr.Sym = lib.scm.Intern(ast.Name)
}
return nil
}
// ASTLet implements let syntaxes.
type ASTLet struct {
From Locator
Kind Keyword
Captures bool
Tail bool
Bindings []*ASTLetBinding
Body []AST
}
// ASTLetBinding implements a let binding.
type ASTLetBinding struct {
From Locator
Binding *EnvBinding
Init AST
}
// Locator implements AST.Locator.
func (ast *ASTLet) Locator() Locator {
return ast.From
}
// Equal implements AST.Equal.
func (ast *ASTLet) Equal(o AST) bool {
oast, ok := o.(*ASTLet)
if !ok {
return false
}
if ast.Kind != oast.Kind || ast.Captures != oast.Captures ||
ast.Tail != oast.Tail || len(ast.Bindings) != len(oast.Bindings) ||
len(ast.Body) != len(oast.Body) {
return false
}
for idx, b := range ast.Bindings {
if b.Binding.Index != oast.Bindings[idx].Binding.Index ||
b.Binding.Frame.Index != oast.Bindings[idx].Binding.Frame.Index {
return false
}
}
for idx, item := range ast.Body {
if !item.Equal(oast.Body[idx]) {
return false
}
}
return true
}
// Type implements AST.Type.
func (ast *ASTLet) Type(ctx types.Ctx) *types.Type {
return ast.Body[len(ast.Body)-1].Type(ctx)
}
// Typecheck implements AST.Typecheck.
func (ast *ASTLet) Typecheck(lib *Library, round int) error {
ctx := make(types.Ctx)
for _, b := range ast.Bindings {
err := b.Init.Typecheck(lib, round)
if err != nil {
return err
}
nt := b.Init.Type(ctx)
if round == 0 {
b.Binding.Type = nt
if ast.Kind == KwLetrec {
lib.recheck = true
}
} else {
if !nt.IsKindOf(b.Binding.Type) {
b.Binding.Type = nt
lib.recheck = true
}
}
}
for _, body := range ast.Body {
err := body.Typecheck(lib, round)
if err != nil {
return err
}
}
return nil
}
// Bytecode implements AST.Bytecode.
func (ast *ASTLet) Bytecode(lib *Library) error {
lib.addPushS(ast.From, len(ast.Bindings), ast.Captures)
for _, binding := range ast.Bindings {
err := binding.Init.Bytecode(lib)
if err != nil {
return err
}
lib.setBinding(binding.From, binding.Binding)
}
for _, item := range ast.Body {
err := item.Bytecode(lib)
if err != nil {
return err
}
}
if !ast.Tail {
lib.addPopS(nil, len(ast.Bindings), ast.Captures)
}
return nil
}
// ASTIf implements if syntax.
type ASTIf struct {
From Locator
Cond AST
True AST
False AST
}
// Locator implements AST.Locator.
func (ast *ASTIf) Locator() Locator {
return ast.From
}
// Equal implements AST.Equal.
func (ast *ASTIf) Equal(o AST) bool {
oast, ok := o.(*ASTIf)
if !ok {
return false
}
if !ast.Cond.Equal(oast.Cond) {
return false
}
if !ast.True.Equal(oast.True) {
return false
}
if ast.False == nil {
if oast.False != nil {
return false
}
} else if oast.False == nil {
return false
} else if !ast.False.Equal(oast.False) {
return false
}
return true
}
// Type implements AST.Type.
func (ast *ASTIf) Type(ctx types.Ctx) *types.Type {
if ast.False == nil {
return types.Unify(ast.Cond.Type(ctx), ast.True.Type(ctx))
}
return types.Unify(ast.True.Type(ctx), ast.False.Type(ctx))
}
// Typecheck implements AST.Typecheck.
func (ast *ASTIf) Typecheck(lib *Library, round int) error {
err := ast.Cond.Typecheck(lib, round)
if err != nil {
return err
}
err = ast.True.Typecheck(lib, round)
if err != nil {
return err
}
if ast.False != nil {
err = ast.False.Typecheck(lib, round)
if err != nil {
return err
}
}
return nil
}
// Bytecode implements AST.Bytecode.
func (ast *ASTIf) Bytecode(lib *Library) error {
labelFalse := lib.newLabel()
labelEnd := lib.newLabel()
err := ast.Cond.Bytecode(lib)
if err != nil {
return err
}
if ast.False == nil {
// (if cond t)
instr := lib.addInstr(ast.From, OpIfNot, nil, 0)
instr.J = labelEnd.I
err = ast.True.Bytecode(lib)
if err != nil {
return err
}
} else {
// (if cond t f)
instr := lib.addInstr(ast.From, OpIfNot, nil, 0)
instr.J = labelFalse.I
err = ast.True.Bytecode(lib)
if err != nil {
return err
}
instr = lib.addInstr(nil, OpJmp, nil, 0)
instr.J = labelEnd.I
lib.addLabel(labelFalse)
err = ast.False.Bytecode(lib)
if err != nil {
return err
}
}
lib.addLabel(labelEnd)
return nil
}
// ASTApply implements apply syntax.
type ASTApply struct {
From Locator
Lambda AST
Args AST
Tail bool
}
// Locator implements AST.Locator.
func (ast *ASTApply) Locator() Locator {
return ast.From
}
// Equal implements AST.Equal.
func (ast *ASTApply) Equal(o AST) bool {
oast, ok := o.(*ASTApply)
if !ok {
return false
}
return ast.Lambda.Equal(oast.Lambda) &&
ast.Args.Equal(oast.Args) &&
ast.Tail == oast.Tail
}
// Type implements AST.Type.
func (ast *ASTApply) Type(ctx types.Ctx) *types.Type {
t := ast.Lambda.Type(ctx)
if t.Enum != types.EnumLambda {
return types.Unspecified
}
return t.Return
}
// Typecheck implements AST.Typecheck.
func (ast *ASTApply) Typecheck(lib *Library, round int) error {
err := ast.Lambda.Typecheck(lib, round)
if err != nil {
return err
}
return ast.Args.Typecheck(lib, round)
}
// Bytecode implements AST.Bytecode.
func (ast *ASTApply) Bytecode(lib *Library) error {
err := ast.Lambda.Bytecode(lib)
if err != nil {
return err
}
// Create a call frame.
lib.addInstr(nil, OpPushF, nil, 0)
// Compile arguments.
err = ast.Args.Bytecode(lib)
if err != nil {
return err
}
// Push apply scope.
lib.addInstr(nil, OpPushA, nil, 0)
lib.addCall(nil, -1, ast.Tail)
return nil
}
// ASTCall implements function call syntax.
type ASTCall struct {
From Locator
Inline bool
InlineOp Operand
Func AST
ArgFrame *EnvFrame
Args []AST
ArgLocs []Locator
Tail bool
}
func (ast *ASTCall) String() string {
str := "("
if ast.Inline {
str += ast.InlineOp.String()
} else {
str += fmt.Sprintf("%v", ast.Func)
}
for _, arg := range ast.Args {
str += fmt.Sprintf(" %v", arg)
}
return str + ")"
}
// Locator implements AST.Locator.
func (ast *ASTCall) Locator() Locator {
return ast.From
}
// Equal implements AST.Equal.
func (ast *ASTCall) Equal(o AST) bool {
oast, ok := o.(*ASTCall)
if !ok {
return false
}
if !ast.Func.Equal(oast.Func) {
return false
}
if len(ast.Args) != len(oast.Args) {
return false
}
for idx, arg := range ast.Args {
if !arg.Equal(oast.Args[idx]) {
return false
}
}
return ast.Tail == oast.Tail
}
var inlineCallTypes = map[Operand]inlineParametrizer{
OpCons: inlineParametrizerCons,
OpAdd: inlineParametrizerNumber,
OpSub: inlineParametrizerNumber,
OpMul: inlineParametrizerNumber,
OpDiv: inlineParametrizerNumber,
OpEq: inlineParametrizerBoolean,
OpLt: inlineParametrizerBoolean,
OpGt: inlineParametrizerBoolean,
OpLe: inlineParametrizerBoolean,
OpGe: inlineParametrizerBoolean,
}
type inlineParametrizer func(params []*types.Type) *types.Type
func inlineParametrizerCons(params []*types.Type) *types.Type {
return &types.Type{
Enum: types.EnumPair,
Car: types.Unspecified,
Cdr: types.Unspecified,
}
}
func inlineParametrizerNumber(params []*types.Type) *types.Type {
var result *types.Type
for _, param := range params {
result = types.Coerce(result, param)
}
return result
}
func inlineParametrizerBoolean(params []*types.Type) *types.Type {
return types.Boolean
}
func inlineParametrizerUnspecified(params []*types.Type) *types.Type {
return types.Unspecified
}
func inlineParametrizerCastNumber(params []*types.Type) *types.Type {
return types.Number
}
func inlineParametrizerCastSymbol(params []*types.Type) *types.Type {
return types.Symbol
}
// Type implements AST.Type.
func (ast *ASTCall) Type(ctx types.Ctx) *types.Type {
var params []*types.Type
for _, arg := range ast.Args {
params = append(params, arg.Type(ctx))
}
if ast.Inline {
parametrizer, ok := inlineCallTypes[ast.InlineOp]
if !ok {
panic(fmt.Sprintf("unknown inline operand: %v", ast.InlineOp))
}
return parametrizer(params)
}
t := ast.Func.Type(ctx)
if t.Enum != types.EnumLambda {
return types.Unspecified
}
if t.Parametrizer == nil {
return t.Return
}
return t.Parametrizer.Parametrize(ctx, params)
}
// Typecheck implements AST.Typecheck.
func (ast *ASTCall) Typecheck(lib *Library, round int) error {
ctx := make(types.Ctx)
var ft *types.Type
if ast.Inline {
sym := lib.scm.Intern(ast.InlineOp.String())
ft = sym.GlobalType
if ft.IsA(types.Unspecified) {
return ast.From.Errorf("unknown inline operand: %v", ast.InlineOp)
}
} else {
err := ast.Func.Typecheck(lib, round)
if err != nil {
return err
}
ft = ast.Func.Type(ctx)
}
if ft.IsA(types.Unspecified) || ft.IsA(types.Any) {
return nil
}
if ft.Enum != types.EnumLambda {
return ast.Func.Locator().Errorf("invalid procedure: %s", ft)
}
if len(ast.Args) < ft.MinArgs() {
return ast.From.Errorf("too few arguments: got %v, need %v",
len(ast.Args), ft.MinArgs())
}
if len(ast.Args) > ft.MaxArgs() {
return ast.From.Errorf("too many arguments: got %v, max %v",
len(ast.Args), ft.MaxArgs())
}
if lib.scm.pragmaVerboseTypecheck {
var argOfs []int
sig := fmt.Sprintf("(%v", ast.Func)
for _, arg := range ft.Args {
sig += " "
argOfs = append(argOfs, len(sig))
sig += fmt.Sprintf("%v", arg)
}
sig += ")"
ast.From.Infof("typecheck: calling (%s", ast.Func)
for _, arg := range ast.Args {
fmt.Printf(" %v", arg)
}
fmt.Println(")")
var prefix string
var prefixes []string
for idx, arg := range ast.Args {
for len(prefix) < argOfs[idx] {
prefix += " "
}
prefixes = append(prefixes, prefix)
fmt.Printf("%s%s\n", prefix, arg)
prefix += "|"
}
fmt.Println(prefix)
fmt.Println(sig)
fmt.Println(prefix)
for i := len(ast.Args) - 1; i >= 0; i-- {
arg := ast.Args[i]
at := arg.Type(ctx)
if i < len(ft.Args) {
fmt.Printf("%s%v IsKindOf %v: %v\n", prefixes[i], at,
ft.Args[i], at.IsKindOf(ft.Args[i]))
}
}
}
// Check argument types.
for idx, arg := range ast.Args {
at := arg.Type(ctx)
if idx < len(ft.Args) {
if !at.IsKindOf(ft.Args[idx]) {
return arg.Locator().Errorf("invalid argument %v, expected %v",
at, ft.Args[idx])
}
}
}
return nil
}
// Bytecode implements AST.Bytecode.
func (ast *ASTCall) Bytecode(lib *Library) error {
var self *lambdaCompilation
const calltAsJump bool = false
if !ast.Inline {
id, ok := ast.Func.(*ASTIdentifier)
if ok && id.Binding != nil && lib.current != nil &&
lib.current.Self == id.Init {
self = lib.current
}
err := ast.Func.Bytecode(lib)
if err != nil {
return nil
}
// Create call frame.
if !(calltAsJump && self != nil && ast.Tail) {
lib.addInstr(ast.From, OpPushF, nil, 0)
}
}
// Push argument scope.
if len(ast.Args) > 0 {
lib.addInstr(ast.From, OpPushS, nil, len(ast.Args))
}
// Evaluate arguments.
for idx, arg := range ast.Args {
err := arg.Bytecode(lib)
if err != nil {
return err
}
lib.addInstr(ast.ArgLocs[idx], OpLocalSet, nil, ast.ArgFrame.Index+idx)
}
if ast.Inline {
lib.addInstr(ast.From, ast.InlineOp, nil, 0)
lib.addInstr(ast.From, OpPopS, nil, len(ast.Args))
} else if calltAsJump && self != nil && ast.Tail {
if false {
fmt.Printf(" - jmp %v\n", self.Label)
for idx, b := range self.ArgBindings {
fmt.Printf(" - %v: %d.%d(%v) %v\n",
idx, b.Frame.Index, b.Index, b.Disabled, b.Type)
}
self.Env.Print()
}
instr := lib.addInstr(nil, OpJmp, nil, 0)
instr.J = self.Label.I
} else {
lib.addCall(nil, len(ast.Args), ast.Tail)
}
return nil
}
// ASTCallUnary implements inlined unary function calls.
type ASTCallUnary struct {
From Locator
Op Operand
I int
Arg AST
}
// Locator implements AST.Locator.
func (ast *ASTCallUnary) Locator() Locator {
return ast.From
}
// Equal implements AST.Equal.
func (ast *ASTCallUnary) Equal(o AST) bool {
oast, ok := o.(*ASTCallUnary)
if !ok {
return false
}
return ast.Op == oast.Op && ast.Arg.Equal(oast.Arg)
}
var inlineUnaryTypes = map[Operand]inlineParametrizer{
OpPairp: inlineParametrizerBoolean,
OpNullp: inlineParametrizerBoolean,
OpZerop: inlineParametrizerBoolean,
OpNot: inlineParametrizerBoolean,
OpCar: inlineParametrizerUnspecified,
OpCdr: inlineParametrizerUnspecified,
OpAddConst: inlineParametrizerNumber,
OpSubConst: inlineParametrizerNumber,
OpMulConst: inlineParametrizerNumber,
OpCastNumber: inlineParametrizerCastNumber,
OpCastSymbol: inlineParametrizerCastSymbol,
}
// Type implements AST.Type.
func (ast *ASTCallUnary) Type(ctx types.Ctx) *types.Type {
params := []*types.Type{
ast.Arg.Type(ctx),
types.InexactInteger,
}
parametrizer, ok := inlineUnaryTypes[ast.Op]
if !ok {
panic(fmt.Sprintf("unknown inline unary operand: %v", ast.Op))
}
return parametrizer(params)
}
var inlineUnaryArgTypes = map[Operand]*types.Type{
OpPairp: types.Any,
OpCar: types.Pair,
OpCdr: types.Pair,
OpNullp: types.Any,
OpZerop: types.Any,
OpNot: types.Any,
OpAddConst: types.Number,
OpSubConst: types.Number,
OpMulConst: types.Number,
OpCastNumber: types.Any,
OpCastSymbol: types.Any,
}
// Typecheck implements AST.Typecheck.
func (ast *ASTCallUnary) Typecheck(lib *Library, round int) error {
ctx := make(types.Ctx)
err := ast.Arg.Typecheck(lib, round)
if err != nil {
return err
}
at, ok := inlineUnaryArgTypes[ast.Op]
if !ok {
panic(fmt.Sprintf("unknown inline unary operand: %v", ast.Op))
}
t := ast.Arg.Type(ctx)
if !t.IsKindOf(at) {
return ast.From.Errorf("invalid argument %v, expected %v", t, at)
}
return nil
}
// Bytecode implements AST.Bytecode.
func (ast *ASTCallUnary) Bytecode(lib *Library) error {
err := ast.Arg.Bytecode(lib)
if err != nil {
return err
}
lib.addInstr(ast.From, ast.Op, nil, ast.I)
return nil
}
// ASTLambda implements lambda syntax.
type ASTLambda struct {
From Locator
Name *Identifier
Args Args
ArgBindings []*EnvBinding
Body []AST
Env *Env
Captures bool
Define bool
Flags Flags
}
// Locator implements AST.Locator.
func (ast *ASTLambda) Locator() Locator {
return ast.From
}
// Equal implements AST.Equal.
func (ast *ASTLambda) Equal(o AST) bool {
oast, ok := o.(*ASTLambda)
if !ok {
return false
}
if !ast.Args.Equal(oast.Args) {
return false
}
if len(ast.Body) != len(oast.Body) {
return false
}
for idx, body := range ast.Body {
if !body.Equal(oast.Body[idx]) {
return false
}
}
return ast.Captures == oast.Captures && ast.Flags == oast.Flags
}
// Type implements AST.Type.
func (ast *ASTLambda) Type(ctx types.Ctx) *types.Type {
t := &types.Type{
Enum: types.EnumLambda,
Return: ast.Body[len(ast.Body)-1].Type(ctx),
Parametrizer: ast,
}
for _, arg := range ast.Args.Fixed {
t.Args = append(t.Args, arg.Type)
}
if ast.Args.Rest != nil {
t.Rest = ast.Args.Rest.Type
}
return t
}
// Parametrize implements types.Parametrizer.
func (ast *ASTLambda) Parametrize(ctx types.Ctx,
params []*types.Type) *types.Type {
if ctx[ast] {
return types.Unspecified
}
ctx[ast] = true
defer func() {
ctx[ast] = false
}()
// Bind argument types.
if len(params) < ast.Args.Min || len(params) > ast.Args.Max {
return types.Unspecified
}
for i := 0; i < len(ast.Args.Fixed); i++ {
ast.ArgBindings[i].Type = params[i]
}
if len(params) > len(ast.Args.Fixed) {
// Rest.
var rt *types.Type
for i := len(ast.Args.Fixed); i < len(params); i++ {
rt = types.Unify(rt, params[i])
}
ast.ArgBindings[len(ast.Args.Fixed)].Type = &types.Type{
Enum: types.EnumPair,
Car: rt,
Cdr: types.Unspecified,
}
}
result := types.Unspecified
for _, a := range ast.Body {
result = a.Type(ctx)
}
return result
}
// Typecheck implements AST.Typecheck.
func (ast *ASTLambda) Typecheck(lib *Library, round int) error {
for _, body := range ast.Body {
err := body.Typecheck(lib, round)
if err != nil {
return err
}
}
if ast.Name == nil {
return nil
}
ctx := make(types.Ctx)
sym := lib.scm.Intern(ast.Name.Name)
nt := ast.Type(ctx)
if round == 0 {
if !sym.GlobalType.IsA(types.Unspecified) {
return ast.From.Errorf("redefining symbol '%s'", ast.Name.Name)
}
sym.GlobalType = nt
lib.recheck = true
} else {
if !nt.IsA(sym.GlobalType) {
sym.GlobalType = nt
lib.recheck = true
}
}
return nil