YACC|BISON :How do I manipulate parse tree?

Question

The goal of my application is to validate an sql code and generate,in the mean time, from that code a formatted one with some modification.
For example this where clause :

where
e.student_name= c.contact_name and ( c.address = " nefta" or c.address=" tozeur ") and
e.age <18

we will have as formatted output something like that :

where e.student_name= c.contact_name
and (c.address=trim("nefta")
or c.address=trim("tozeur") )
and e.age <18

I hope I've explained my aim well

---

The problem is grammars may contain recursive rules which make the rewrite task unreliable ; for instance in my sql grammar i have this :

search_condition         : search_condition OR search_condition{clbck_or}
                         | search_condition AND search_condition{clbck_and}
                         | NOT search_condition {clbck_not}
                         | '(' search_condition ')'{clbck__}
                         | predicate {clbck_pre}
                         ;

Knowing that I specified a precedence priority to solve shift reduce problems

%left OR
%left AND
%left NOT

So back on the last example ; my clause where will be consumed this way:

c.address="nefta"or c.address="tozeur" -> search_condition
(c.address="nefta"or c.address="tozeur")->search_condition
e.student_name= c.contact_name and (c.address="nefta"or c.address="tozeur")-> search_condition
... and e.age<18-> search_condition

You can by the way understand that it's tough to rebuild the input stream referring to callbacks triggered by each reduction cause the order is not the same.

Any help for this problem ?

Answer 1

Your question is a bit vague, so I'm guessing that you actually print in your clbck_or (), etc. The "common" way to which wildplasser has alluded is to use "semantic values", i. e. (untested):

search_condition         : search_condition OR search_condition{$$ = clbck_or($1, $3);}
                         | search_condition AND search_condition{$$ = clbck_and($1, $3);}
                         | NOT search_condition {$$ = clbck_not($2);}
                         | '(' search_condition ')'{$$ = clbck__($2);}
                         | predicate {$$ = clbck_pre($1);}
                         ;

If you're using Bison, the manual has a fine example in the section "Infix Notation Calculator: `calc'". With strings and C, you will have to add some memory handling.