Re: [Gretl-devel] nesting a function call getting a list doesn't work

On Sun, 21 Jun 2015, Sven Schreiber wrote: OK, then maybe I can explain my thinking better by reference to Ignacio's HoltWinters package discussed elsethread. Yes, more or less, though I'd say it's either the user's fault (assuming the function in question is properly documented) or the function author's fault (otherwise). No, that's not my view. Take HoltWinters. This function does some computations, prints out some statistics, and also offers a list return that wraps a couple of series. Maybe I'd like to see the statistics but don't care to accept the generated series, so I don't assign the return value. Before my code modification of February, I'd have got the two series added to my dataset regardless. Surprise! That's not Ignacio's fault, as I see it; it was gretl's fault. With this sort of function, adding the series to the main dataset should be conditional on accepting the list return, not because we think the user is a dummy, but because it's a reasonable expectation that if you don't want and don't ask for the series, you won't get them. Consider by contrast a built-in such as log(), applied to a list. This function does absolutely nothing apart from creating logs of the input series, and offering as return a wrapper for the generated series. Unlike HoltWinters there's never any reason to call such a function unless you want the series it generates. However, you don't necessarily need the list wrapper. It therefore seems a legitimate use-case to call log() without assignment in the expectation that the series you want will be added; otherwise log(List) would just be a no-op. Q: "Why did the logs get added to my dataset when I didn't assign the return?" A: "Well, if you didn't want that then why did you call log()?" The answer here seems to me to have force, but it doesn't have force for HoltWinters, or other contributed functions that print things or plot things besides offering a list return. Allin