bison/examples/java/simple/Calc.y

%language "Java"

%define api.parser.class {Calc}
%define api.parser.public

%define parse.error verbose

%code imports {
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.Reader;
  import java.io.StreamTokenizer;
}

%code {
  public static void main (String[] args) throws IOException
  {
    CalcLexer l = new CalcLexer (System.in);
    Calc p = new Calc (l);
    if (!p.parse ())
      System.exit (1);
  }
}

/* Bison Declarations */
%token <Integer> NUM "number"
%type  <Integer> exp

%nonassoc '='       /* comparison            */
%left '-' '+'
%left '*' '/'
%precedence NEG     /* negation--unary minus */
%right '^'          /* exponentiation        */

/* Grammar follows */
%%
input:
  line
| input line
;

line:
  '\n'
| exp '\n'           { System.out.println ($exp); }
| error '\n'
;

exp:
  NUM                { $$ = $1; }
| exp '=' exp
  {
    if ($1.intValue () != $3.intValue ())
      yyerror ("calc: error: " + $1 + " != " + $3);
  }
| exp '+' exp        { $$ = $1 + $3;  }
| exp '-' exp        { $$ = $1 - $3;  }
| exp '*' exp        { $$ = $1 * $3;  }
| exp '/' exp        { $$ = $1 / $3;  }
| '-' exp  %prec NEG { $$ = -$2; }
| exp '^' exp        { $$ = (int) Math.pow ($1, $3); }
| '(' exp ')'        { $$ = $2; }
| '(' error ')'      { $$ = 1111; }
| '!'                { $$ = 0; return YYERROR; }
| '-' error          { $$ = 0; return YYERROR; }
;


%%
class CalcLexer implements Calc.Lexer {

  StreamTokenizer st;

  public CalcLexer (InputStream is)
  {
    st = new StreamTokenizer (new InputStreamReader (is));
    st.resetSyntax ();
    st.eolIsSignificant (true);
    st.whitespaceChars ('\t', '\t');
    st.whitespaceChars (' ', ' ');
    st.wordChars ('0', '9');
  }

  public void yyerror (String s)
  {
    System.err.println (s);
  }

  Integer yylval;

  public Object getLVal () {
    return yylval;
  }

  public int yylex () throws IOException {
    int ttype = st.nextToken ();
    switch (ttype)
      {
      case StreamTokenizer.TT_EOF:
        return EOF;
      case StreamTokenizer.TT_EOL:
        return (int) '\n';
      case StreamTokenizer.TT_WORD:
        yylval = new Integer (st.sval);
        return NUM;
      default:
        return ttype;
      }
  }
}