[phc-general] Why isn't Tree_transform::pre_statement()implemented
Satyam at satyam.com.ar
Wed Aug 2 16:41:19 CEST 2006
----- Original Message -----
From: "Edsko de Vries" <edsko at phpcompiler.org>
> Aaah. Please allow me to refer you to tutorial3,
> and in particular section "A Subtlety" (towards the end of the tutorial).
> problem you're experiencing is exactly what I've tried to explain there
> (although perhaps I didn't do a very good job, it *is* indeed a subtlety
> :-) If
> you still don't understand what's happening after reading that, please do
> back to me.
When I read it I couldn't figure out what was the point. Now that it
happened to me I see it.
> Yes, as explained in tutorial 3, that is one solution, although the better
> solution is to use a post-transform rather than a pre-transform; but that
> not be possible, depending on the transform. Also, if you _are_
> implementing a
> pre_transform, you don't need to call transform; calling pre_transform is
Indeed, I thought I needed to pick pre_ because I need to set up something
before carying on with the transform, but then it proved not enough.
Actually I have a stack in which I save the state of what I am doing, a
state that influences what goes after. Nevertheless, I find that is not
enough at least in two cases.
For example, in an if, I have to provide the same stack for the expr, the
iftrue and the iffalse parts. Right now, I have the problem that in the
iffalse part I get the stack as set by the iftrue part so I think I would
have to redefine the children_if method to make a copy of the stack on entry
and give each branch the same node. I could pop the stack in the post_
method at each step, but I also need to check that the stack ends in the
same state on each branch even if it gets to different depths. Same with
I'll try that out, though I will also break it into two passes, one to
analyze what has to be done and make sure everything is consistent, leaving
information along the tree in the 'attrs' map and then doing the actual
transformations in the second pass. Perhaps later I might find that I can
do the analyzis on the pre_methods and then the transformation on the
post_methods, but I bumped into a couple of things that I can't get a clear
image of when trying to do everything at once.
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