ANTLR4:输入时没有可行的替代方案(生成AST)

Question

我有一个简单的ANTLR代码

whilestmt: 'while' exp 'do' stmt;                       
forstmt: 'for' VAR 'equal' exp TO exp 'do' stmt;
dosthstmt: 'something';                             
stmt: whilestmt|forstmt|dosthstmt;
exp:   exp ADDOP exp    #addterm
       | fact           #factterm
       ;    
fact:  INTLIT           #intlit
       | VAR            #idlist
       | LB exp RB      #bracexp
       ;
WS : [ trn]+ -> skip ; 
INTLIT : [0-9]+ ;  
ADDOP: '+';
LB: '(';
RB: ')';
TO: 'to' | 'down to';
VAR: [a-z]+;

我的Scala代码:

import java.io.{PrintWriter,File}
import java.lang.RuntimeException
import org.antlr.v4.runtime.ANTLRFileStream
import org.antlr.v4.runtime.CommonTokenStream
object Main {
   def main(args:Array[String]):Unit = {
      val source = new ANTLRFileStream("test.txt")
      val lexer = new ExpLexer(source)
      val tokens = new CommonTokenStream(lexer)
      val parser = new ExpParser(tokens)
      val exp_parsetree = parser.exp() 
      //println(exptree.getClass)
      val astgen = new ASTGeneration()
      val exp_ast = exp_parsetree.accept(astgen)
      println(exp_ast)
   }
}
class ASTGeneration extends ExpBaseVisitor[ExpAST] {  
    override def visitWhilestmt(ctx: ExpParser.WhilestmtContext) = { 
        WhileAST(ctx.getChild(0).getText,ctx.exp.accept(this),ctx.getChild(1).getText,ctx.stmt.accept(this))
    }    
    override def visitForstmt(ctx: ExpParser.ForstmtContext) = {
        ForAST("for", ctx.VAR.accept(this), "equal", ctx.exp(1).accept(this), ctx.TO.accept(this) ,ctx.exp(1).accept(this), "do", ctx.stmt.accept(this))
    }  
    override def visitDosthstmt(ctx: ExpParser.DosthstmtContext) = {
        DosthAST("do something")
    }   
    override def visitAddterm (ctx:ExpParser.AddtermContext) =
        AddtermAST(ctx.exp(0).accept(this),ctx.getChild(1).getText,ctx.exp(1).accept(this))
    override def visitFactterm(ctx:ExpParser.FacttermContext) =
        ctx.fact.accept(this)
    override def visitIntlit(ctx:ExpParser.IntlitContext) =
        IntlitAST(ctx.INTLIT.getText.toInt)
    override def visitIdlist(ctx:ExpParser.IdlistContext) =
        IdAST(ctx.VAR.getText.toString)
    override def visitBracexp(ctx:ExpParser.BracexpContext) = 
        ctx.exp.accept(this) 
    }
trait ExpAST
case class WhileAST(op:String,exp1:ExpAST, op2:String,exp2:ExpAST) extends ExpAST
case class ForAST(forr:String,varr:ExpAST, equal:String,exp1:ExpAST,to:ExpAST,exp2:ExpAST,doo:String,stmt:ExpAST) extends ExpAST
case class DosthAST(stmt:String) extends ExpAST
case class AddtermAST(left:ExpAST,op:String,right:ExpAST) extends ExpAST 
case class IntlitAST(value:Int) extends ExpAST
case class IdAST(id:String) extends ExpAST`

我正在尝试生成AST
我的输入:while 3 do something和错误:
line 1:0 no viable alternative at input 'while' null
但是输入3+4，它工作得很好，结果是AddtermAST(IntlitAST(3),+,IntlitAST(4))

有谁能帮我一下吗?谢谢(抱歉我的英语不好)

Answer 1

语法的入口点是exp规则。

val exp_parsetree = parser.exp()

很可能，你想用

val exp_parsetree = parser.stmt()

当然，输入的3+4可能无法正确解析——它只是一个简单的exp。