COP 5021 Lecture -*- Outline -*-

* Attributes

** What are attributes?
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            ATTRIBUTES

defn: an *attribute* is


Two kinds of attributes:

    Synthesized: (passed up)
             AST's value computed
               from attributes of subtrees

    Inherited: (passed down)
             AST's value given to it
               from its parent in the AST
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        ... a property of an AST (can be any Java value in JastAdd)

** Examples of Synthesized Attributes
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          SYNTHESIZED ATTRIBUTE EXAMPLE
// file Unparse.jrag
aspect Unparse {

	syn String Program.unparse();
	syn String S.unparse();
	syn String Expr.unparse();
	syn String Op.unparse();
	syn String Label.unparse();

	eq Program.unparse() = getS().unparse();
	eq CompoundS.unparse() { 
		StringBuffer s = new StringBuffer();
		s.append("{\n");
		int len = getNumSList();
		for (int i = 0; i < len; i++) {
			s.append(getSList(i).unparse());
			if (i < len-1) { s.append(";\n"); }	
		}
		s.append("\n}");
		return s.toString();
	}
	eq VarRefExpr.unparse() { return getContents();}
	eq NumLitExpr.unparse() { return getContents();}
	eq BoolLitExpr.unparse() { return getContents();}
	eq ABinaryExpr.unparse() { return "(" + getLeft().unparse() + " " + getOp().unparse() + " " + getRight().unparse() + ")";}

	eq NotExpr.unparse() { return "not " + getExpr().unparse();}
	eq LogicExpr.unparse() { return "(" + getLeft().unparse() + " " + getOp().unparse() + " " + getRight().unparse() + ")";}
	eq RelExpr.unparse() { return "(" + getLeft().unparse() + " " + getOp().unparse() + " " + getRight().unparse() + ")";}

	eq SkipS.unparse() = "[skip]^" + getLabelAST().unparse();
	eq AssignS.unparse() {
		return "[" + getVar() + " := " + getExpr().unparse() + "]" 
			+ "^" + getLabelAST().unparse();
	}

        // ... similarly, see Unparse.jrag
}
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   Show how to program this, show also toString in Unparse.jrag

** inherited attribute example
   Q: Suppose we want to have indentation for prettyprinting?
   For this use an inherited attribute

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// file PrettyPrint.jrag
import utility.PPUtility;

aspect PrettyPrint {

    inh int S.nestingLevel();
    eq Program.getS().nestingLevel() = 0;
    eq CompoundS.getSList(int index).nestingLevel() = nestingLevel()+1;
    eq IfS.getS1().nestingLevel() = nestingLevel();
    eq IfS.getS2().nestingLevel() = nestingLevel();
    eq WhileS.getS().nestingLevel() = nestingLevel();
    eq StmtBlock.getS().nestingLevel() = 0;  // just for sake of form

    // ...

    syn String Program.prettyPrint();
    syn String S.prettyPrint();
    syn String Expr.prettyPrint();
    syn String Op.prettyPrint();
    syn String Label.prettyPrint();
    // ... eqs use nestingLevel()...
}
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        show how this is done in PrettyPrint.jrag

        Q: Why does nestingLevel need to be inherited?