[Gretl-devel] Re: weird function arg bug

On Sun, 24 Oct 2021, Sven Schreiber wrote: Specifically, the second case fails with the error message: "heylist: argument 1 is of the wrong type (is list, should be series)" In the second case gretl notices that the statement as a whole involves assignment to a list object. Trying to be helpful, it therefore "casts" the argument to diff(), namely LRM, to a single-member list. This _would_ in fact be helpful if the statement were of the simpler form list oi = diff(LRM) # call it case B Why? Because diff(LRM), without a cast to list for the argument, produces an anonymous series, and only named series (members of the dataset) can be put into lists. Clearly, gretl is not clever enough here: in the heylist() context "diff(LRM)" _should_ produce an anonymous series result; this expression is supposed to create an argument to a function that wants a series. Gretl doesn't understand that, unlike case B, "diff(LRM)" occurs in an "opaque" context as an argument to heylist(). So what's the fix? Either (a) gretl has to figure out how to detect opacity of context, or (b) we drop the series-to-list cast business altogether, in which case statements of the "case B" type would fail. Arguably, case B statements ought to fail. But we probably need to check if that would break any existing function packages. And if we decide to scrap the cast we should probably amend the doc for functions such as diff() to point out that you can't assign to a list if the RHS is just a series. (To be clear, it's not a problem if the RHS is a single-member list, only if it's a series as such.) Allin