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*: [mg69539] 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*: "David Park" <djmp at earthlink.net>*Date*: Fri, 15 Sep 2006 06:44:53 -0400 (EDT)

Nasser, What about a more specific test? xc = Table[i, {i, 1, 3}]; x = 5; If[x === b && xc[[10]] == 4, Print["True"], Print["False"], Print["Can't decide"]] False If[NumericQ[b] && x == b && xc[[10]] == 4, Print["True"], Print["False"], Print["Can't decide"]] False David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: Nasser Abbasi [mailto:nma at 12000.org] To: mathgroup at smc.vnet.net 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