(*
 * This file illustrates how to create an attribute-grammar-style definintion
 * in RSL.  Syntactically, the notation is slightly different than most
 * standard CFG notations, however these syntactic differences are quite minor.
 * The differences are:
 *
 *     (1) Elements of the RHS of a rule must be separated with one of the two
 *         normal RSL operators 'and' or ',', rather than the more typical
 *         blanks.
 *     (2) The normal RSL attribute selection operator '.:' is used to select
 *         the value of symbol attributes rather than the more typical '.'.
 *     (3) The RSL keyword "is" is used in place of the more standard '::='
 *         rule separator (actually, we allow "::=" now).
 *
 * What does not work here is the use of '{' and '}' to enclose semantic
 * actions.  I tried to fit this syntactic use of curly braces into the RSL
 * grammar, but it was a pain given the normal use of curlies as the tuple
 * constructor.
 *
 * Note that this grammar is patterned directly after the examples in CSC 451
 * lectures notes week 9.  See ~gfisher/classes/451/lectures/9.ps.
 *
 *  Cf ./term-factor-does-work.rsl and ./term-factor-doesnt-work.rsl.
 *)

module TermFactorAttributeGrammar;

    (*
     * Attribute definitions.
     *)
    define obj attribute type:Type;
    define obj attribute valu:Value;

    (*
     * Attribute type definitions.
     *)
    obj Type =  string;
    obj Value =  number;


    (*
     * Grammar and semantic action definitions.
     *)

    rule E = e:E "+" t:T
		{
                 this.:type = (if e.:type = t.:type
                                then e.:type else "ERROR");
                 this.:valu = e.:valu + t.:valu;
		}
    end E;

    rule E = t:T 
		{
        	 this.:type = t.:type;
                 this.:valu = t.:valu;
		}
    end;

    rule T = t:T "*" f:F;
    rule T' = f:F;
    rule F = "x";

end TermFactorAttributeGrammar;

module TermFactorAttributeGrammarAlt;

    (*
     * Attribute definitions.
     *)
    define obj attribute type:Type;
    define obj attribute valu:Value;

    (*
     * Attribute type definitions.
     *)
    obj Type =  string;
    obj Value =  number;


    (*
     * Grammar and semantic action definitions.
     *)

    rule E = e:E "+" t:T
                {this.:type = (if e.:type = t.:type
                                then e.:type else "ERROR");
                 this.:valu = e.:valu + t.:valu;}
           | t:T
                {this.:type = t.:type;
                 this.:valu = t.:valu;}
    end E;

    rule E =
    end E;

    rule T = t:T "*" f:F;
    rule T' = f:F;
    rule F = "x";

end TermFactorAttributeGrammarAlt;