tools/src/tint/intrinsic/parser/parser.go - dawn - Git at Google

 // Copyright 2021 The Tint Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 // Package parser provides a basic parser for the Tint builtin definition
 // language
 package parser

 import (
 	"fmt"
 	"strconv"

 	"dawn.googlesource.com/dawn/tools/src/tint/intrinsic/ast"
 	"dawn.googlesource.com/dawn/tools/src/tint/intrinsic/lexer"
 	"dawn.googlesource.com/dawn/tools/src/tint/intrinsic/tok"
 )

 // Parse produces a list of tokens for the given source code
 func Parse(source, filepath string) (*ast.AST, error) {
 	runes := []rune(source)
 	tokens, err := lexer.Lex(runes, filepath)
 	if err != nil {
 		return nil, err
 	}

 	p := parser{tokens: tokens}
 	return p.parse()
 }

 type parser struct {
 	tokens []tok.Token
 	err    error
 }

 func (p *parser) parse() (*ast.AST, error) {
 	out := ast.AST{}
 	var attributes ast.Attributes
 	for p.err == nil {
 		t := p.peek(0)
 		if t == nil {
 			break
 		}
 		switch t.Kind {
 		case tok.Attr:
 			attributes = append(attributes, p.attributes()...)
 		case tok.Enum:
 			if len(attributes) > 0 {
 				p.err = fmt.Errorf("%v unexpected attribute", attributes[0].Source)
 			}
 			out.Enums = append(out.Enums, p.enumDecl())
 		case tok.Match:
 			if len(attributes) > 0 {
 				p.err = fmt.Errorf("%v unexpected attribute", attributes[0].Source)
 			}
 			out.Matchers = append(out.Matchers, p.matcherDecl())
 		case tok.Type:
 			out.Types = append(out.Types, p.typeDecl(attributes))
 			attributes = nil
 		case tok.Function:
 			out.Builtins = append(out.Builtins, p.builtinDecl(attributes))
 			attributes = nil
 		case tok.Operator:
 			out.Operators = append(out.Operators, p.operatorDecl(attributes))
 			attributes = nil
 		case tok.Initializer:
 			out.Initializers = append(out.Initializers, p.initializerDecl(attributes))
 			attributes = nil
 		case tok.Converter:
 			out.Converters = append(out.Converters, p.converterDecl(attributes))
 			attributes = nil
 		default:
 			p.err = fmt.Errorf("%v unexpected token '%v'", t.Source, t.Kind)
 		}
 		if p.err != nil {
 			return nil, p.err
 		}
 	}
 	return &out, nil
 }

 func (p *parser) enumDecl() ast.EnumDecl {
 	p.expect(tok.Enum, "enum declaration")
 	name := p.expect(tok.Identifier, "enum name")
 	e := ast.EnumDecl{Source: name.Source, Name: string(name.Runes)}
 	p.expect(tok.Lbrace, "enum declaration")
 	for p.err == nil && p.match(tok.Rbrace) == nil {
 		e.Entries = append(e.Entries, p.enumEntry())
 	}
 	return e
 }

 func (p *parser) enumEntry() ast.EnumEntry {
 	decos := p.attributes()
 	name := p.expect(tok.Identifier, "enum entry")
 	return ast.EnumEntry{Source: name.Source, Attributes: decos, Name: string(name.Runes)}
 }

 func (p *parser) matcherDecl() ast.MatcherDecl {
 	p.expect(tok.Match, "matcher declaration")
 	name := p.expect(tok.Identifier, "matcher name")
 	m := ast.MatcherDecl{Source: name.Source, Name: string(name.Runes)}
 	p.expect(tok.Colon, "matcher declaration")
 	if p.peekIs(1, tok.Dot) { // enum list
 		for p.err == nil {
 			m.Options.Enums = append(m.Options.Enums, p.memberName())
 			if p.match(tok.Or) == nil {
 				break
 			}
 		}
 	} else { // type list
 		for p.err == nil {
 			m.Options.Types = append(m.Options.Types, p.templatedName())
 			if p.match(tok.Or) == nil {
 				break
 			}
 		}
 	}
 	return m
 }

 func (p *parser) typeDecl(decos ast.Attributes) ast.TypeDecl {
 	p.expect(tok.Type, "type declaration")
 	name := p.expect(tok.Identifier, "type name")
 	m := ast.TypeDecl{
 		Source:     name.Source,
 		Attributes: decos,
 		Name:       string(name.Runes),
 	}
 	if p.peekIs(0, tok.Lt) {
 		m.TemplateParams = p.templateParams()
 	}
 	return m
 }

 func (p *parser) attributes() ast.Attributes {
 	var out ast.Attributes
 	for p.match(tok.Attr) != nil && p.err == nil {
 		name := p.expect(tok.Identifier, "attribute name")
 		var values []any
 		if p.match(tok.Lparen) != nil {
 		loop:
 			for p.err == nil {
 				t := p.next()
 				switch t.Kind {
 				case tok.Rparen:
 					break loop
 				case tok.String:
 					values = append(values, string(t.Runes))
 				case tok.Integer:
 					i, _ := strconv.ParseInt(string(t.Runes), 10, 64)
 					values = append(values, int(i))
 				case tok.Float:
 					f, _ := strconv.ParseFloat(string(t.Runes), 64)
 					values = append(values, f)
 				default:
 					p.err = fmt.Errorf("%v invalid attribute value kind: %v", t.Source, t.Kind)
 					return nil
 				}
 				if p.match(tok.Comma) == nil {
 					break
 				}
 			}
 			p.expect(tok.Rparen, "attribute values")
 		}
 		out = append(out, ast.Attribute{
 			Source: name.Source,
 			Name:   string(name.Runes),
 			Values: values,
 		})
 	}
 	return out
 }

 func (p *parser) builtinDecl(decos ast.Attributes) ast.IntrinsicDecl {
 	p.expect(tok.Function, "function declaration")
 	name := p.expect(tok.Identifier, "function name")
 	f := ast.IntrinsicDecl{
 		Source:     name.Source,
 		Kind:       ast.Builtin,
 		Attributes: decos,
 		Name:       string(name.Runes),
 	}
 	if p.peekIs(0, tok.Lt) {
 		f.TemplateParams = p.templateParams()
 	}
 	f.Parameters = p.parameters()
 	if p.match(tok.Arrow) != nil {
 		ret := p.templatedName()
 		f.ReturnType = &ret
 	}
 	return f
 }

 func (p *parser) operatorDecl(decos ast.Attributes) ast.IntrinsicDecl {
 	p.expect(tok.Operator, "operator declaration")
 	name := p.next()
 	f := ast.IntrinsicDecl{
 		Source:     name.Source,
 		Kind:       ast.Operator,
 		Attributes: decos,
 		Name:       string(name.Runes),
 	}
 	if p.peekIs(0, tok.Lt) {
 		f.TemplateParams = p.templateParams()
 	}
 	f.Parameters = p.parameters()
 	if p.match(tok.Arrow) != nil {
 		ret := p.templatedName()
 		f.ReturnType = &ret
 	}
 	return f
 }

 func (p *parser) initializerDecl(decos ast.Attributes) ast.IntrinsicDecl {
 	p.expect(tok.Initializer, "initializer declaration")
 	name := p.next()
 	f := ast.IntrinsicDecl{
 		Source:     name.Source,
 		Kind:       ast.Initializer,
 		Attributes: decos,
 		Name:       string(name.Runes),
 	}
 	if p.peekIs(0, tok.Lt) {
 		f.TemplateParams = p.templateParams()
 	}
 	f.Parameters = p.parameters()
 	if p.match(tok.Arrow) != nil {
 		ret := p.templatedName()
 		f.ReturnType = &ret
 	}
 	return f
 }

 func (p *parser) converterDecl(decos ast.Attributes) ast.IntrinsicDecl {
 	p.expect(tok.Converter, "converter declaration")
 	name := p.next()
 	f := ast.IntrinsicDecl{
 		Source:     name.Source,
 		Kind:       ast.Converter,
 		Attributes: decos,
 		Name:       string(name.Runes),
 	}
 	if p.peekIs(0, tok.Lt) {
 		f.TemplateParams = p.templateParams()
 	}
 	f.Parameters = p.parameters()
 	if p.match(tok.Arrow) != nil {
 		ret := p.templatedName()
 		f.ReturnType = &ret
 	}
 	return f
 }

 func (p *parser) parameters() ast.Parameters {
 	l := ast.Parameters{}
 	p.expect(tok.Lparen, "function parameter list")
 	if p.match(tok.Rparen) == nil {
 		for p.err == nil {
 			l = append(l, p.parameter())
 			if p.match(tok.Comma) == nil {
 				break
 			}
 		}
 		p.expect(tok.Rparen, "function parameter list")
 	}
 	return l
 }

 func (p *parser) parameter() ast.Parameter {
 	attributes := p.attributes()
 	if p.peekIs(1, tok.Colon) {
 		// name type
 		name := p.expect(tok.Identifier, "parameter name")
 		p.expect(tok.Colon, "parameter type")
 		return ast.Parameter{
 			Source:     name.Source,
 			Name:       string(name.Runes),
 			Attributes: attributes,
 			Type:       p.templatedName(),
 		}
 	}
 	// type
 	ty := p.templatedName()
 	return ast.Parameter{
 		Source:     ty.Source,
 		Attributes: attributes,
 		Type:       ty,
 	}
 }

 func (p *parser) string() string {
 	s := p.expect(tok.String, "string")
 	return string(s.Runes)
 }

 func (p *parser) memberName() ast.MemberName {
 	owner := p.expect(tok.Identifier, "member name")
 	p.expect(tok.Dot, "member name")
 	member := p.expect(tok.Identifier, "member name")
 	return ast.MemberName{
 		Source: member.Source,
 		Owner:  string(owner.Runes),
 		Member: string(member.Runes),
 	}
 }

 func (p *parser) templatedName() ast.TemplatedName {
 	name := p.expect(tok.Identifier, "type name")
 	m := ast.TemplatedName{Source: name.Source, Name: string(name.Runes)}
 	if p.match(tok.Lt) != nil {
 		for p.err == nil {
 			m.TemplateArgs = append(m.TemplateArgs, p.templatedName())
 			if p.match(tok.Comma) == nil {
 				break
 			}
 		}
 		p.expect(tok.Gt, "template argument type list")
 	}
 	return m
 }

 func (p *parser) templateParams() ast.TemplateParams {
 	t := ast.TemplateParams{}
 	p.expect(tok.Lt, "template parameter list")
 	for p.err == nil && p.peekIs(0, tok.Identifier) {
 		t = append(t, p.templateParam())
 	}
 	p.expect(tok.Gt, "template parameter list")
 	return t
 }

 func (p *parser) templateParam() ast.TemplateParam {
 	name := p.match(tok.Identifier)
 	t := ast.TemplateParam{
 		Source: name.Source,
 		Name:   string(name.Runes),
 	}
 	if p.match(tok.Colon) != nil {
 		t.Type = p.templatedName()
 	}
 	p.match(tok.Comma)
 	return t
 }

 func (p *parser) expect(kind tok.Kind, use string) tok.Token {
 	if p.err != nil {
 		return tok.Invalid
 	}
 	t := p.match(kind)
 	if t == nil {
 		if len(p.tokens) > 0 {
 			p.err = fmt.Errorf("%v expected '%v' for %v, got '%v'",
 				p.tokens[0].Source, kind, use, p.tokens[0].Kind)
 		} else {
 			p.err = fmt.Errorf("expected '%v' for %v, but reached end of file", kind, use)
 		}
 		return tok.Invalid
 	}
 	return *t
 }

 func (p *parser) ident(use string) string {
 	return string(p.expect(tok.Identifier, use).Runes)
 }

 func (p *parser) match(kind tok.Kind) *tok.Token {
 	if p.err != nil || len(p.tokens) == 0 {
 		return nil
 	}
 	t := p.tokens[0]
 	if t.Kind != kind {
 		return nil
 	}
 	p.tokens = p.tokens[1:]
 	return &t
 }

 func (p *parser) next() *tok.Token {
 	if p.err != nil {
 		return nil
 	}
 	if len(p.tokens) == 0 {
 		p.err = fmt.Errorf("reached end of file")
 	}
 	t := p.tokens[0]
 	p.tokens = p.tokens[1:]
 	return &t
 }

 func (p *parser) peekIs(i int, kind tok.Kind) bool {
 	t := p.peek(i)
 	if t == nil {
 		return false
 	}
 	return t.Kind == kind
 }

 func (p *parser) peek(i int) *tok.Token {
 	if len(p.tokens) <= i {
 		return nil
 	}
 	return &p.tokens[i]
 }
	// Copyright 2021 The Tint Authors.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	// Package parser provides a basic parser for the Tint builtin definition
	// language
	package parser

	import (
	"fmt"
	"strconv"

	"dawn.googlesource.com/dawn/tools/src/tint/intrinsic/ast"
	"dawn.googlesource.com/dawn/tools/src/tint/intrinsic/lexer"
	"dawn.googlesource.com/dawn/tools/src/tint/intrinsic/tok"
	)

	// Parse produces a list of tokens for the given source code
	func Parse(source, filepath string) (*ast.AST, error) {
	runes := []rune(source)
	tokens, err := lexer.Lex(runes, filepath)
	if err != nil {
	return nil, err
	}

	p := parser{tokens: tokens}
	return p.parse()
	}

	type parser struct {
	tokens []tok.Token
	err error
	}

	func (p parser) parse() (ast.AST, error) {
	out := ast.AST{}
	var attributes ast.Attributes
	for p.err == nil {
	t := p.peek(0)
	if t == nil {
	break
	}
	switch t.Kind {
	case tok.Attr:
	attributes = append(attributes, p.attributes()...)
	case tok.Enum:
	if len(attributes) > 0 {
	p.err = fmt.Errorf("%v unexpected attribute", attributes[0].Source)
	}
	out.Enums = append(out.Enums, p.enumDecl())
	case tok.Match:
	if len(attributes) > 0 {
	p.err = fmt.Errorf("%v unexpected attribute", attributes[0].Source)
	}
	out.Matchers = append(out.Matchers, p.matcherDecl())
	case tok.Type:
	out.Types = append(out.Types, p.typeDecl(attributes))
	attributes = nil
	case tok.Function:
	out.Builtins = append(out.Builtins, p.builtinDecl(attributes))
	attributes = nil
	case tok.Operator:
	out.Operators = append(out.Operators, p.operatorDecl(attributes))
	attributes = nil
	case tok.Initializer:
	out.Initializers = append(out.Initializers, p.initializerDecl(attributes))
	attributes = nil
	case tok.Converter:
	out.Converters = append(out.Converters, p.converterDecl(attributes))
	attributes = nil
	default:
	p.err = fmt.Errorf("%v unexpected token '%v'", t.Source, t.Kind)
	}
	if p.err != nil {
	return nil, p.err
	}
	}
	return &out, nil
	}

	func (p *parser) enumDecl() ast.EnumDecl {
	p.expect(tok.Enum, "enum declaration")
	name := p.expect(tok.Identifier, "enum name")
	e := ast.EnumDecl{Source: name.Source, Name: string(name.Runes)}
	p.expect(tok.Lbrace, "enum declaration")
	for p.err == nil && p.match(tok.Rbrace) == nil {
	e.Entries = append(e.Entries, p.enumEntry())
	}
	return e
	}

	func (p *parser) enumEntry() ast.EnumEntry {
	decos := p.attributes()
	name := p.expect(tok.Identifier, "enum entry")
	return ast.EnumEntry{Source: name.Source, Attributes: decos, Name: string(name.Runes)}
	}

	func (p *parser) matcherDecl() ast.MatcherDecl {
	p.expect(tok.Match, "matcher declaration")
	name := p.expect(tok.Identifier, "matcher name")
	m := ast.MatcherDecl{Source: name.Source, Name: string(name.Runes)}
	p.expect(tok.Colon, "matcher declaration")
	if p.peekIs(1, tok.Dot) { // enum list
	for p.err == nil {
	m.Options.Enums = append(m.Options.Enums, p.memberName())
	if p.match(tok.Or) == nil {
	break
	}
	}
	} else { // type list
	for p.err == nil {
	m.Options.Types = append(m.Options.Types, p.templatedName())
	if p.match(tok.Or) == nil {
	break
	}
	}
	}
	return m
	}

	func (p *parser) typeDecl(decos ast.Attributes) ast.TypeDecl {
	p.expect(tok.Type, "type declaration")
	name := p.expect(tok.Identifier, "type name")
	m := ast.TypeDecl{
	Source: name.Source,
	Attributes: decos,
	Name: string(name.Runes),
	}
	if p.peekIs(0, tok.Lt) {
	m.TemplateParams = p.templateParams()
	}
	return m
	}

	func (p *parser) attributes() ast.Attributes {
	var out ast.Attributes
	for p.match(tok.Attr) != nil && p.err == nil {
	name := p.expect(tok.Identifier, "attribute name")
	var values []any
	if p.match(tok.Lparen) != nil {
	loop:
	for p.err == nil {
	t := p.next()
	switch t.Kind {
	case tok.Rparen:
	break loop
	case tok.String:
	values = append(values, string(t.Runes))
	case tok.Integer:
	i, _ := strconv.ParseInt(string(t.Runes), 10, 64)
	values = append(values, int(i))
	case tok.Float:
	f, _ := strconv.ParseFloat(string(t.Runes), 64)
	values = append(values, f)
	default:
	p.err = fmt.Errorf("%v invalid attribute value kind: %v", t.Source, t.Kind)
	return nil
	}
	if p.match(tok.Comma) == nil {
	break
	}
	}
	p.expect(tok.Rparen, "attribute values")
	}
	out = append(out, ast.Attribute{
	Source: name.Source,
	Name: string(name.Runes),
	Values: values,
	})
	}
	return out
	}

	func (p *parser) builtinDecl(decos ast.Attributes) ast.IntrinsicDecl {
	p.expect(tok.Function, "function declaration")
	name := p.expect(tok.Identifier, "function name")
	f := ast.IntrinsicDecl{
	Source: name.Source,
	Kind: ast.Builtin,
	Attributes: decos,
	Name: string(name.Runes),
	}
	if p.peekIs(0, tok.Lt) {
	f.TemplateParams = p.templateParams()
	}
	f.Parameters = p.parameters()
	if p.match(tok.Arrow) != nil {
	ret := p.templatedName()
	f.ReturnType = &ret
	}
	return f
	}

	func (p *parser) operatorDecl(decos ast.Attributes) ast.IntrinsicDecl {
	p.expect(tok.Operator, "operator declaration")
	name := p.next()
	f := ast.IntrinsicDecl{
	Source: name.Source,
	Kind: ast.Operator,
	Attributes: decos,
	Name: string(name.Runes),
	}
	if p.peekIs(0, tok.Lt) {
	f.TemplateParams = p.templateParams()
	}
	f.Parameters = p.parameters()
	if p.match(tok.Arrow) != nil {
	ret := p.templatedName()
	f.ReturnType = &ret
	}
	return f
	}

	func (p *parser) initializerDecl(decos ast.Attributes) ast.IntrinsicDecl {
	p.expect(tok.Initializer, "initializer declaration")
	name := p.next()
	f := ast.IntrinsicDecl{
	Source: name.Source,
	Kind: ast.Initializer,
	Attributes: decos,
	Name: string(name.Runes),
	}
	if p.peekIs(0, tok.Lt) {
	f.TemplateParams = p.templateParams()
	}
	f.Parameters = p.parameters()
	if p.match(tok.Arrow) != nil {
	ret := p.templatedName()
	f.ReturnType = &ret
	}
	return f
	}

	func (p *parser) converterDecl(decos ast.Attributes) ast.IntrinsicDecl {
	p.expect(tok.Converter, "converter declaration")
	name := p.next()
	f := ast.IntrinsicDecl{
	Source: name.Source,
	Kind: ast.Converter,
	Attributes: decos,
	Name: string(name.Runes),
	}
	if p.peekIs(0, tok.Lt) {
	f.TemplateParams = p.templateParams()
	}
	f.Parameters = p.parameters()
	if p.match(tok.Arrow) != nil {
	ret := p.templatedName()
	f.ReturnType = &ret
	}
	return f
	}

	func (p *parser) parameters() ast.Parameters {
	l := ast.Parameters{}
	p.expect(tok.Lparen, "function parameter list")
	if p.match(tok.Rparen) == nil {
	for p.err == nil {
	l = append(l, p.parameter())
	if p.match(tok.Comma) == nil {
	break
	}
	}
	p.expect(tok.Rparen, "function parameter list")
	}
	return l
	}

	func (p *parser) parameter() ast.Parameter {
	attributes := p.attributes()
	if p.peekIs(1, tok.Colon) {
	// name type
	name := p.expect(tok.Identifier, "parameter name")
	p.expect(tok.Colon, "parameter type")
	return ast.Parameter{
	Source: name.Source,
	Name: string(name.Runes),
	Attributes: attributes,
	Type: p.templatedName(),
	}
	}
	// type
	ty := p.templatedName()
	return ast.Parameter{
	Source: ty.Source,
	Attributes: attributes,
	Type: ty,
	}
	}

	func (p *parser) string() string {
	s := p.expect(tok.String, "string")
	return string(s.Runes)
	}

	func (p *parser) memberName() ast.MemberName {
	owner := p.expect(tok.Identifier, "member name")
	p.expect(tok.Dot, "member name")
	member := p.expect(tok.Identifier, "member name")
	return ast.MemberName{
	Source: member.Source,
	Owner: string(owner.Runes),
	Member: string(member.Runes),
	}
	}

	func (p *parser) templatedName() ast.TemplatedName {
	name := p.expect(tok.Identifier, "type name")
	m := ast.TemplatedName{Source: name.Source, Name: string(name.Runes)}
	if p.match(tok.Lt) != nil {
	for p.err == nil {
	m.TemplateArgs = append(m.TemplateArgs, p.templatedName())
	if p.match(tok.Comma) == nil {
	break
	}
	}
	p.expect(tok.Gt, "template argument type list")
	}
	return m
	}

	func (p *parser) templateParams() ast.TemplateParams {
	t := ast.TemplateParams{}
	p.expect(tok.Lt, "template parameter list")
	for p.err == nil && p.peekIs(0, tok.Identifier) {
	t = append(t, p.templateParam())
	}
	p.expect(tok.Gt, "template parameter list")
	return t
	}

	func (p *parser) templateParam() ast.TemplateParam {
	name := p.match(tok.Identifier)
	t := ast.TemplateParam{
	Source: name.Source,
	Name: string(name.Runes),
	}
	if p.match(tok.Colon) != nil {
	t.Type = p.templatedName()
	}
	p.match(tok.Comma)
	return t
	}

	func (p *parser) expect(kind tok.Kind, use string) tok.Token {
	if p.err != nil {
	return tok.Invalid
	}
	t := p.match(kind)
	if t == nil {
	if len(p.tokens) > 0 {
	p.err = fmt.Errorf("%v expected '%v' for %v, got '%v'",
	p.tokens[0].Source, kind, use, p.tokens[0].Kind)
	} else {
	p.err = fmt.Errorf("expected '%v' for %v, but reached end of file", kind, use)
	}
	return tok.Invalid
	}
	return *t
	}

	func (p *parser) ident(use string) string {
	return string(p.expect(tok.Identifier, use).Runes)
	}

	func (p parser) match(kind tok.Kind) tok.Token {
	if p.err != nil \|\| len(p.tokens) == 0 {
	return nil
	}
	t := p.tokens[0]
	if t.Kind != kind {
	return nil
	}
	p.tokens = p.tokens[1:]
	return &t
	}

	func (p parser) next() tok.Token {
	if p.err != nil {
	return nil
	}
	if len(p.tokens) == 0 {
	p.err = fmt.Errorf("reached end of file")
	}
	t := p.tokens[0]
	p.tokens = p.tokens[1:]
	return &t
	}

	func (p *parser) peekIs(i int, kind tok.Kind) bool {
	t := p.peek(i)
	if t == nil {
	return false
	}
	return t.Kind == kind
	}

	func (p parser) peek(i int) tok.Token {
	if len(p.tokens) <= i {
	return nil
	}
	return &p.tokens[i]
	}