[antlr-interest] tree transformation question (if-elif-else -> if-else)

[Klaas Hofstra]

Hi,

I have a problem with tree transformations that must have been solved before 
because it seems to me that it occurs frequently when converting one language 
to another.

I need to convert the following pseudo-code:

if expression
  statements
elif expression
  statements
elif expression
  statements
else
  statements

into:

if expression
  statements
else
  if expression
    statements
  else
    if expression
      statements
    else
      statements

Translated into trees, I need to transform the tree :

tree1 =
(IFBLOCK  (IF  E1  S1) (ELIF  E2  S2) (ELIF  E3  S3) (ELSE  S4))

into:

tree2 = 
(IFBLOCK  (IF  E1  S1)  (ELSE  (IFBLOCK  (IF E2 S2)  (ELSE  
(IFBLOCK  (IF E3  S3) (ELSE  S4))))))

, where E=EXPRESSION, S=STATEMENTS

My problem is that the rewrite rule for ELIF  is something like:

(ELIF  E  S) -> (ELSE  (IFBLOCK  (IF E S)  subtree_of_next_elif_or_else)

When traversing the tree from left to right with a treeparser,  
'subtree_of_next_elif_or_else' is not available when it is needed.

How can this problem be solved?

Thanks in advance,

Klaas