javagrammarbisonyaccparser-generator

Bison java examples


Does anyone knows if there are some tutorials and/or examples of using GNU Bison with Java over the net. I've searched through the net. But i didn't manage to find anything. I have tried to implement an example but I could not compile it (since I need a lexer also). Here is my example:

%{
  static void main(String[] args) {
    yyparse();
  }
%}

%union {
  int     number;
  char    operator;
}

%language "Java"

%token<number>   NUMBER 
%token<operator> OPERATOR  

%type <number> exp

%left OPERATOR
%%

input
    : /* Empty string */
    | exp { System.out.print("Result >> " + $1); }
    ;

exp
    : NUMBER
    | exp OPERATOR exp { 
        switch($2) {
            case '+': $$ = $1 + $3; break;
            case '-': $$ = $1 - $3; break;
            case '*': $$ = $1 * $3; break;
            case '/': $$ = $1 / $3; break;
        }
    }

%%

Any help would be appreciate!


Solution

  • Unfortunately, virtually all public examples for Bison's Java generator are hidden in the testsuite. If you are adventurous, after ./configure && make do make check TESTSUITEFLAGS="-d -k java". This will run all tests with the keyword (-k) "Java" and not remove the sandbox directories after successful tests (-d) so you get beneath tests/testsuite.dir a bunch of directories with grammars, generated Java source code and compiled classes. One example from Bison 2.5:

    /* Infix notation calculator--calc */
    %language "Java"
    %name-prefix "Calc"
    %define parser_class_name "Calc"
    %define public
    
    
    %code {
    
      public static void main (String args[]) throws IOException
      {
        CalcLexer l = new CalcLexer (System.in);
        Calc p = new Calc (l);
        p.parse ();
      }
    
    }
    
    %code imports {
      import java.io.StreamTokenizer;
      import java.io.InputStream;
      import java.io.InputStreamReader;
      import java.io.Reader;
      import java.io.IOException;
    }
    
    /* Bison Declarations */
    %token <Integer> NUM "number"
    %type  <Integer> exp
    
    %nonassoc '=' /* comparison            */
    %left '-' '+'
    %left '*' '/'
    %left NEG     /* negation--unary minus */
    %right '^'    /* exponentiation        */
    
    /* Grammar follows */
    %%
    input:
      line
    | input line
    ;
    
    line:
      '\n'
    | exp '\n'
    | error '\n'
    ;
    
    exp:
      NUM                { $$ = $1;                                             }
    | exp '=' exp
      {
        if ($1.intValue () != $3.intValue ())
          yyerror ( "calc: error: " + $1 + " != " + $3);
      }
    | exp '+' exp        { $$ = new Integer ($1.intValue () + $3.intValue ());  }
    | exp '-' exp        { $$ = new Integer ($1.intValue () - $3.intValue ());  }
    | exp '*' exp        { $$ = new Integer ($1.intValue () * $3.intValue ());  }
    | exp '/' exp        { $$ = new Integer ($1.intValue () / $3.intValue ());  }
    | '-' exp  %prec NEG { $$ = new Integer (-$2.intValue ());                  }
    | exp '^' exp        { $$ = new Integer ((int)
                                             Math.pow ($1.intValue (),
                                                       $3.intValue ()));        }
    | '(' exp ')'        { $$ = $2;                                             }
    | '(' error ')'      { $$ = new Integer (1111);                             }
    | '!'                { $$ = new Integer (0); return YYERROR;                }
    | '-' error          { $$ = new Integer (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 (9, 9);
        st.whitespaceChars (32, 32);
        st.wordChars (48, 57);
      }
    
    
      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 ();
    
        if (ttype == st.TT_EOF)
          return Calc.EOF;
    
        else if (ttype == st.TT_EOL)
          {
    
            return (int) '\n';
          }
    
        else if (ttype == st.TT_WORD)
          {
            yylval = new Integer (st.sval);
            return Calc.NUM;
          }
    
        else
          return st.ttype;
      }
    
    
    
    }
    
    
    class Position {
      public int line;
      public int token;
    
      public Position ()
      {
        line = 0;
        token = 0;
      }
    
      public Position (int l, int t)
      {
        line = l;
        token = t;
      }
    
      public boolean equals (Position l)
      {
        return l.line == line && l.token == token;
      }
    
      public String toString ()
      {
        return Integer.toString (line) + "." + Integer.toString(token);
      }
    
      public int lineno ()
      {
        return line;
      }
    
      public int token ()
      {
        return token;
      }
    }