Should be easy to generate (therefore it is not done by hand in practice)

https://svn.cs.uu.nl:12443/repos/StrategoXT/trunk/StrategoXT/ssl/spec/parenthesize.str

Submitted on 27 March 2004 at 09:08

STR-40, martin:
Code Generation solves all your problems. Parenthesize stuff should not be written by hand.

STR-40, martin:
What does the tool `restorebracket’ in the sdf-bundle?

STR-40, adam:
well done!

STR-40, adam:
Martin’s release notes:

     * trans/sdf2parenthesize.str: new tool to generate a Stratego
     transformation tool that adds the necessary parentheses to an
     abstract syntax tree. The information is obtained from an SDF
     syntax definition.

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

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

     A relative priority related example:
     ----------------------------------------------------
     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)))
     ----------------------------------------------------

     The tool supports:
     o relative priorities
       --------------------------------------------------
           Exp "&&"  Exp -> Exp
       >   Exp "||"  Exp -> Exp
       --------------------------------------------------
     
     o groups of associative productions
       --------------------------------------------------
         {left:
           Exp "*" Exp -> Exp
           Exp "/" Exp -> Exp
         } 
       > {left:
           Exp "+" Exp -> Exp
           Exp "-" Exp -> Exp
         }
       --------------------------------------------------

     o Associativity attributes: non-assoc, assoc, left, right.
       --------------------------------------------------
         Exp "+"   Exp -> Exp  {left, cons("Plus")}
       --------------------------------------------------

     o Kernel SDF associativities
       --------------------------------------------------
         prod1 assoc prod2
       --------------------------------------------------

     To be honest, this is all support because the SDF normalizer is applied ;) .

     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 IfThenElse(_, IfThen(_, _, _),_) is pretty-printed correctly as:

     --------------------------------------------------
     if a then (if b then c) else d
     --------------------------------------------------

     then you still need to implement this be hand. I don't have a clue
     how I could automate this in the generator, since the {prefer}
     attributes are not really declarative.

     Bug reports are welcome.