---++ Introduction

=sdf2parenthesize= generates a Stratego transformation tool that adds the 
necessary parentheses to an abstract syntax tree. The information is obtained 
from an SDF syntax definition.

---++ Example

For example, if Plus is declared to left associative, then the
following rule will be generated:

<verbatim>
  ExpParenthesize :
	 Plus(q_15, Plus(o_15, p_15)) -> Plus(q_15, Parenthetical(Plus(o_15, p_15)))
</verbatim>

A relative priority related example:
<verbatim>
  ExpParenthesize :
	 Mul(Plus(v_2, w_2), u_2) -> Mul(Parenthetical(Plus(v_2, w_2)), u_2)

  ExpParenthesize :
	 Mul(t_2, Plus(v_2, w_2)) -> Mul(t_2, Parenthetical(Plus(v_2, w_2)))
</verbatim>

The tool supports:

---++++ Relative priorities

<verbatim>
	 Exp "&&"  Exp -> Exp
  > Exp "||"  Exp -> Exp
</verbatim>

---++++ Groups of associative productions

<verbatim>
	 {left:
		 Exp "*" Exp -> Exp
		 Exp "/" Exp -> Exp
	 }
  > {left:
		 Exp "+" Exp -> Exp
		 Exp "-" Exp -> Exp
	 }
</verbatim>

---++++ Associativity attributes: non-assoc, assoc, left, right.

<verbatim>
  Exp "+"	Exp -> Exp  {left, cons("Plus")}
</verbatim>

---++++ Kernel SDF associativities

<verbatim>
  prod1 assoc prod2
</verbatim>

---++ Open Issues


Does this solve all the parentheses related problems? No,
unfortunately not. The tool does not support {prefer} attributes,
which are for example used in the dangling else problem.

So, if you want to make sure that
<verbatim>
  IfThenElse(_, IfThen(_, _, _), _)
</verbatim>
is pretty-printed correctly as:
<verbatim>
  if a then (if b then c) else d
</verbatim>
then you still need to implement this be hand. Notice that you can import the generated rules in this
handwritten tool. I don't have a clue now I could automate these issues in the generator, 
since the ={prefer}= attributes are not really declarative.