Re: How to tell Mathematica to stop conditional testing in an If statment if one condition is niether True or False? McCarthy evaluation rules? 'and then' test?

*To*: mathgroup at smc.vnet.net*Subject*: [mg69566] Re: [mg69525] How to tell Mathematica to stop conditional testing in an If statment if one condition is niether True or False? McCarthy evaluation rules? 'and then' test?*From*: "Chris Chiasson" <chris at chiasson.name>*Date*: Fri, 15 Sep 2006 06:46:45 -0400 (EDT)*References*: <200609141057.GAA21660@smc.vnet.net>

use === On 9/14/06, Nasser Abbasi <nma at 12000.org> wrote: > I can better describe this with simple example: > > ------------- code ------------ > > Remove["Global`*"]; > xc = Table[i, {i, 1, 3}] > x = 5; > If[x == b && xc[[10]] == 4, Print["True"], Print["False"], Print["Can't > decide"]] > > ----- end code ------------- > In the above, 'x==b' is neither True nor False, since 'b' has no numerical > value. > > But what I want is when this happens, for Mathematica to NOT continue with > the testing if xc[[10]]==4 is True (because even if it is True, it will > not change the outcome, which is can't decide. > > I am looking for something like 'and then' which says to test the next > condition only if the one just tested was true. > > The interesting thing is that if 'b' had a value, say 7, which makes the > first test (the x==b) to be False, then Mathematica does the right thing, > and will not try to check the xc[[10]]==4 condition. I need it to do the > same thing when also the result of the check is 'undecided', not just > 'False' or 'True'. > > Is there a way to do this? Notice in the example above, I get the error > that xc[[10]] is out of bound, but still get the can't decide message. > > It is clear to me that the way Mathematica does it now is not the right way. > I do not see why it tries to check for xc[[10]]==4 when it will not make a > difference to the final result. > > any thoughts? > > thanks, > Nasser > > > > -- http://chris.chiasson.name/

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