> heres the structure of: select(from_obj=[t1, t2, t1.join(t2)])
>
> select +---> t1 <-------------+
> |---> t2 <------------|
> +---> join of t1/t2 ---+
>
> t2 and t1 both have two parents, and there are two paths to each of t1
> and t2 from the head select. so its not a tree in the strict sense.
>
> or another one:
>
> s1 = t1.select().alias('s1')
> s2 = t1.select().alias('s2')
>
> s3 = s1.union(s2) (two paths to t1: s3->s1->t1, s3->s2->t1)
>
> any kind of subquery which references a table at a higher level falls
> into this category.
>
hmm. it's still a tree, just the nodes contain same things (t1). There
are no cyclic paths to _same_ node in the expression.
like x+y+23*(x+1) --- x is used/pointed twice but the expression is
still a tree.
is there any case where some t1 (or even subexpr) is translated once in
one way, and then in another branch in another way? e.g. like in the
above x+y+... first x is to be replaced with its value, but second with
its name (say because its in round brackets - in some now-invented
syntax of mine ).
i think there is some mixup between what the expression is, as grammar,
and what it actualy means, and u're trying to solve/combine both in one
thing/visitor. maybe also what it should mean _after the processing.
While they should be all separate notions, somehow.
eh, i'm just throwing ideas / alternative view points to play with...
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