However, that treatment of the "const" modifier cannot work when the series passed is the one named "const" (with ID number 0). That series is supposed to be automatically available at all levels of function execution,

Well, but only if the dataset context is passed on to the called function, right? Otherwise no series is available inside, not even "const" (ID 0). This is the background of what I'm trying to achieve, with a little bit of borderline hacking. I'm working with MPI and (sometimes, not always in my general meta function) need to pass on the dataset context. And I thought the safest way is to use the series that always exists, namely "const".

This issue hasn't been reported before, which is not surprising since passing series 0 as an argument is in general pointless, since it's already available everywhere and is of no interest other than as the intercept in a regression. I think I see a way of making it harmless but I need to do some more testing before I'm sure.

Thanks. Again, the interest here is not the "const" series per se, but the idea is to "piggyback" the dataset context on an arbitrarily chosen series. But I think I can work around this particular problem; for example, two hackish pieces of syntax that work instead of the passed arg "const" are:

1) "(dataset)[1]" - assumes at least one other series, which is OK; not that "dataset[1]" didn't work

2) "deflist(const)[1]" - uglier, but also works

(More background explanation: I first tried to use a gretl list that is of more direct interest, but the problem was that this doesn't work in the also covered case that no dataset is present. That is, I can use the function arg specification 'series s[null]' and the null default also works without an active dataset, but 'list L[null]' yields an error then. I know this is because of the special behavior of lists, which always exist even when "null-ed" or omitted. But that's causing a problem here, hence my workaround with "const".) 

If it's too dangerous to accommodate the passing of just "const" (and since usually there isn't much point in it), perhaps it's better to just ban it? Or perhaps ban the combination of passing "const" to a function that uses the const modifier for its arg?

thanks

sven