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Adder.g4

grammar Adder; WS : [ \t\r\n]+ -> skip ; Num : ('-')?[0-9]+ | ('-')?[0-9]+'.'[0-9]+ ; expr : expr '+' expr # addExpr | Num # numExpr ; start : expr EOF ; Error : . ;

Adder.java

Adder.java

import  org . antlr . v4 . runtime . * ;
import  org . antlr . v4 . runtime . tree . * ;
import  java . io . * ;

public   class   Adder   {
     public   static   void  main ( String []  args )   throws   IOException   {
         BufferedReader  in  =
          new   BufferedReader ( new   InputStreamReader ( System . in ));
         CharStream  inputStream  =   CharStreams . fromReader ( in );
         AdderLexer  lexer  =   new   AdderLexer ( inputStream );
         CommonTokenStream  commonTokenStream  =   new   CommonTokenStream ( lexer );
         AdderParser  parser  =   new   AdderParser ( commonTokenStream );  
        parser . setErrorHandler ( new   BailErrorStrategy ());

         ParseTree  tree  =  parser . start ();
         AdderInterpreter  interpreter  =   new   AdderInterpreter ();
         Float  result  =  interpreter . visit ( tree );
     System . out . println ( result . toString ());
     }
}

AdderInterpreter.java

AdderInterpreter.java

public   class   AdderInterpreter   extends   AdderBaseVisitor < Float >   {
    @ Override
     public   Float  visitAddExpr ( AdderParser . AddExprContext  ctx )   {
         float  result  =  visit ( ctx . expr ( 0 )). floatValue ()   +
                       visit ( ctx . expr ( 1 )). floatValue ();
         return   Float . valueOf ( result );
     }

    @ Override
     public   Float  visitNumExpr ( AdderParser . NumExprContext  ctx )   {
         return   Float . valueOf ( ctx . Num (). getText ());
     }

    @ Override
     public   Float  visitStart ( AdderParser . StartContext  ctx )   {
         return  visit ( ctx . expr ());
     }
}