Hi, here's a RFC or a feature request, in some sense: Currently a gretl 'list' datatype is strictly different from a 'series' type it seems. So when a user-written function expects a list, you cannot pass it a series. (BTW, it the error message was a little strange: something like "unknown datatype where list was expected", although gretl should recognize its own series type?) But isn't a series really a 1-element list? Wouldn't it actually make sense to not have a different series datatype, just lists with varying numbers of elements? Note that the built-in functions for series already seem to honor this principle, because they accept both series and list datatypes. I think it's good to think about this before gretl 2.0... thanks, sven