Expression trees in galib?

[Magnus Lie Hetland]

I've looked at the tree genome in galib, and it doesn't seem to
distinguish between leaf nodes and internal nodes in any significant
way... It seems to me that for expression trees (the norm in GP) it
would be natural to have two template parameters -- one for each of
the two kinds of nodes...

How does one implement expression trees in a reasonable way in galib?
One option is, perhaps, to rig the mutation and crossover operators to
maintain a strict separation between the two; another might be to
implement a redundant node-contents type that can act either as an
operator or as a constant (leaf).

Am I missing an obvious way of doing this? Is anyone else doing GP
with GALib? (I know there are other libraries that have more support
for this sort of thing, but I've got a bit of infrastructure that
already uses galib, so...)

-- 
Magnus Lie Hetland               "Nothing shocks me. I'm a scientist." 
http://hetland.org                                   -- Indiana Jones