func isKeyword(tok token) bool {
	return keywordsStart < tok && tok < keywordsEnd
}
isKeyword returns if tok is in the keywords range
package proto
import (
	"strings"
)
type token int
const (
	tILLEGAL token = iota
	tEOF
	tWS
	tIDENT
	tSEMICOLON    
	tCOLON        
	tEQUALS       
	tQUOTE        
	tSINGLEQUOTE  
	tLEFTPAREN    
	tRIGHTPAREN   
	tLEFTCURLY    
	tRIGHTCURLY   
	tLEFTSQUARE   
	tRIGHTSQUARE  
	tCOMMENT      
	tLESS         
	tGREATER      
	tCOMMA        
	tDOT          
	keywordsStart
	tSYNTAX
	tSERVICE
	tRPC
	tRETURNS
	tMESSAGE
	tIMPORT
	tPACKAGE
	tOPTION
	tREPEATED
	tWEAK
	tPUBLIC
	tONEOF
	tMAP
	tRESERVED
	tENUM
	tSTREAM
	tOPTIONAL
	tGROUP
	tEXTENSIONS
	tEXTEND
	tREQUIRED
	keywordsEnd
)
const typeTokens = "double float int32 int64 uint32 uint64 sint32 sint64 fixed32 sfixed32 sfixed64 bool string bytes"