[Gretl-users] hiperf model for loops (was Re: Renaming variables not allowed within a loop)

On Sun, 20 Mar 2016, Sven Schreiber wrote: [Note: I've put the devel-list in cc, because I guess this discussion may get quite technical, and that we may want to continue it there, so sorry for the cross-posting.] I've begun to think that we may wan to introduce an option to the loop command to distinguish between a "safe" and a "hi-perf" mode. Let me explain: initally, the loop .. endloop construct used to imply a simple repetition of whatever was inside, with only a few specific caveats and checks: eg, some commands were disallowed on the ground of common sense (eg, nulldata), some others would partially change their meaning (eg "print" in progressive mode) etc. This has been silently changing for a while: as Hansl has grown in ambitions, it's become evident that sometimes you must use loops for specialised tasks which involve very few different instructions, but should ideally run as fast as possible. Typically, those instructiona are the various incarnations of "genr" and, possibly, basic estimation commands such as ols or var. Think for example of implementing a bootstrap procedure or MCMC; you'll never need the full array of Hansl syntax inside those: genr and user-written functions are normally all you need, but you'll want those instruction to run as fast as possible. In the past year or so, Allin has been working on "compiling" loops, that is, change the way hansl handles them going from mere repetition of their contents to a more efficient treatment. This is very nice, but very complex, since it's very hard to optimise a few things the hansl language provides (eg string substitution) without risking complete breakage. Therefore, I'm now thinking about the possibility of introducing something like a --hi-perf option to "loop", which would disallow some instructions but would make it possible to run the allowed ones at full speed without having to bother with too many checks. What do you guys think? ------------------------------------------------------- Riccardo (Jack) Lucchetti Dipartimento di Scienze Economiche e Sociali (DiSES) Università Politecnica delle Marche (formerly known as Università di Ancona) r.lucchetti(a)univpm.it http://www2.econ.univpm.it/servizi/hpp/lucchetti -------------------------------------------------------