/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright (C) 2001 Gerwin Klein <lsf@jflex.de>                          *
 * All rights reserved.                                                    *
 *                                                                         *
 * This is a modified version of the example from                          *
 *   http://www.lincom-asg.com/~rjamison/byacc/                            *
 *                                                                         *
 * Thanks to Larry Bell and Bob Jamison for suggestions and comments.      *
 *                                                                         *
 * License: BSD                                                            *
 *                                                                         *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

%{
  import java.io.*;
%}
      
%token NL                    /* newline  */
%token <sval> NUM            /* a number as a string */
%token PLUS MINUS TIMES DIV  /* operators */
%token LPAR RPAR             /* parethesis */

%type <sval> exp

%left MINUS PLUS
%left TIMES DIV
%left NEG          /* negation--unary minus */

%type <sval> line
%start line      
%%

line:  exp   { strExp=$1; $$=$1; }
       ;
      
exp:     NUM                   { $$ = $1; }
       | exp PLUS exp          { $$ = "(add "+$1+" "+$3+")"; }
       | exp MINUS exp         { $$ = "(sub "+$1+" "+$3+")"; }
       | exp TIMES exp         { $$ = "(mul "+$1+" "+$3+")"; }
       | exp DIV exp           { $$ = "(div "+$1+" "+$3+")"; }
       | MINUS exp  %prec NEG  { $$ = "-"+$2; }
       | LPAR exp RPAR         { $$ = $2; }
       ;

%%

  public String strExp;
  
  private Yylex lexer;


  private int yylex () {
    int yyl_return = -1;
    try {
      yylval = new ParserVal(0);
      yyl_return = lexer.yylex();
    }
    catch (IOException e) {
      System.err.println("IO error :"+e);
    }
    return yyl_return;
  }


  public void yyerror (String error) {
    System.err.println ("Error: " + error);
  }


  public Parser(Reader r) {
    lexer = new Yylex(r, this);
  }

/*
public static void main(String args[]) throws IOException {
    //System.out.println("BYACC/Java with JFlex Calculator Demo");

    Parser yyparser;
    
    yyparser = new Parser(new InputStreamReader(System.in));
    yyparser.yyparse();

  }
*/