I just read the section in the manual about operator precedence and I think perhaps I'm even more confused than I was! It details a strict order of precedence which seems to contradict the knowledge that condition evaluation proceeds from left to right and stops as soon as a false one is found.
Maybe I'll try a few test cases. Pete Molly's Revenge <http://www.mollysrevenge.com> On Wed, Oct 5, 2011 at 4:36 PM, stephen barncard < stephenrevoluti...@barncard.com> wrote: > yeah , I don't know, sometimes stuff doesn't work exactly right so I try > something else like > > if a is true > then > > switch > case b = true > case c = true > do whatever > break > end switch > > end if > > or try reversing and/or > > if a is true then > > if (b is true and c is true) then > do whatever > end if > > end if > > I know the above doesn't look right but this has come up many times and > works for me. > > On 5 October 2011 16:25, Pete <p...@mollysrevenge.com> wrote: > > > No, I mean: > > > > If a is true then > > if (b is true or c is true) then > > do whatever > > end if > > end if > > > > I'm pretty sure if a was false, the second condition wouldn't be > evaluated. > > > > But you raise an interesting point - in your example, does the condition > > inside the parens truly get evaluated first? > > > > Pete > > Molly's Revenge <http://www.mollysrevenge.com> > > > > > > > > > > On Wed, Oct 5, 2011 at 3:59 PM, Bob Sneidar <b...@twft.com> wrote: > > > > > Yes, if by nested you mean: > > > a is true and (b is true or c is true) > > > > > > The statement in parenthesis gets evaluated first. > > > > > > Bob > > > > > > > > > On Oct 5, 2011, at 2:20 PM, Pete wrote: > > > > > > > Thanks, that's good to know. I'm looking at using a pretty complex > > > > condition with some of the conditions being trivial but others taking > > up > > > > significant database access so sounds like I should leave the db > access > > > > conditions until last. > > > > > > > > Hmmm, now I wonder if nested if statements make any difference to > this. > > > > Probably not. > > > > > > > > > > > > Pete > > > > Molly's Revenge <http://www.mollysrevenge.com> > > > > > > > > > > > > > > > > > > > > On Wed, Oct 5, 2011 at 1:46 PM, Richard Gaskin > > > > <ambassa...@fourthworld.com>wrote: > > > > > > > >> Pete wrote: > > > >> > > > >> I'm wondering how LC evaluates If statements with multiple > conditions. > > > >>> Are > > > >>> all conditions evaluated before the overall result is checked for > > true > > > or > > > >>> false, or does evaluation proceed left to right and stop as soon as > a > > > >>> condition is found to be false? Whichever method is used, is it > > > affected > > > >>> by > > > >>> some conditions being enclosed in parens? > > > >>> > > > >> > > > >> IIRC from discussions with Dr. Raney many years ago, at some point > he > > > >> implemented an optimization in which the first part of any > > > multi-condition > > > >> expression that satisfies the expression avoids the need for > > evaluation > > > of > > > >> other conditions. This normally follows in left-to-right order, but > > of > > > >> course using parens can alter the evaluation order. > > > >> > > > >> So in this conditional expression: > > > >> > > > >> if the short name of this cd is "Pete" and $user <> "pete" then > > > >> > > > >> If the short name of the card <> "Pete" then the engine wouldn't > > bother > > > >> evaluating $user. > > > >> > > > >> -- > > > >> Richard Gaskin > > > >> Fourth World > > > >> LiveCode training and consulting: http://www.fourthworld.com > > > >> Webzine for LiveCode developers: http://www.LiveCodeJournal.com > > > >> LiveCode Journal blog: http://LiveCodejournal.com/**blog.irv< > > > http://LiveCodejournal.com/blog.irv> > > > >> > > > >> ______________________________**_________________ > > > >> use-livecode mailing list > > > >> use-livecode@lists.runrev.com > > > >> Please visit this url to subscribe, unsubscribe and manage your > > > >> subscription preferences: > > > >> http://lists.runrev.com/**mailman/listinfo/use-livecode< > > > http://lists.runrev.com/mailman/listinfo/use-livecode> > > > >> > > > >> > > > > _______________________________________________ > > > > use-livecode mailing list > > > > use-livecode@lists.runrev.com > > > > Please visit this url to subscribe, unsubscribe and manage your > > > subscription preferences: > > > > http://lists.runrev.com/mailman/listinfo/use-livecode > > > > > > > > > _______________________________________________ > > > use-livecode mailing list > > > use-livecode@lists.runrev.com > > > Please visit this url to subscribe, unsubscribe and manage your > > > subscription preferences: > > > http://lists.runrev.com/mailman/listinfo/use-livecode > > > > > > > > _______________________________________________ > > use-livecode mailing list > > use-livecode@lists.runrev.com > > Please visit this url to subscribe, unsubscribe and manage your > > subscription preferences: > > http://lists.runrev.com/mailman/listinfo/use-livecode > > > > > > -- > > > > Stephen Barncard > San Francisco Ca. USA > > more about sqb <http://www.google.com/profiles/sbarncar> > _______________________________________________ > use-livecode mailing list > use-livecode@lists.runrev.com > Please visit this url to subscribe, unsubscribe and manage your > subscription preferences: > http://lists.runrev.com/mailman/listinfo/use-livecode > > _______________________________________________ use-livecode mailing list use-livecode@lists.runrev.com Please visit this url to subscribe, unsubscribe and manage your subscription preferences: http://lists.runrev.com/mailman/listinfo/use-livecode
