Re: Making a new definition of Equal work with lists as well

*To*: mathgroup at smc.vnet.net*Subject*: [mg63400] Re: Making a new definition of Equal work with lists as well*From*: Bill Rowe <readnewsciv at earthlink.net>*Date*: Thu, 29 Dec 2005 02:57:31 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

On 12/28/05 at 3:55 AM, dan.bernstein at gmail.com wrote: >I'm afraid I didn't give a sufficiently general example in my >question. What I would like to do is to be able to get True/False >results for expressions as general as >{CL[2,3], 5, {CL[4,5], CL[2,2]}, x} == {CL[2,3], 8, {CL[6,7], >CL[9,9]}, y} >that is, lists containing both CLs and other elements, and nested >lists etc. >Making Equal listable wouldn't work because I would then get also a >list (of booleans) as a result. >I think defining Equal for CL[a_, b_] could have "just worked" if >Equal for lists was internally defined to AND the Equal of all >matching pairs, something like >Equal[j_ListQ, k_ListQ]:=If[Length[j]!=Length[k], False, >And@@Table[Equal[j[[i]], k[[i]]], {i, 1, Length[j]}] I would do the above as: Equal[a_List,b_List]:= If[Length@a != Length@b, False, And@@MapThread[Equal, {a,b}]] or Equal[a_List,b_List]:= If[Length@a != Length@b, False, And@@(Equal@@@Transpose@{a,b})] >And I guess I could re-define it this way, but I wonder what the >built-in definition is, and what I stand to lose by overriding it >like that. To me, this is really the key issue. For myself, I am quite reluctant to override any built-in function especially one used as often as Equal. The potential for unintended side effects is always there. So, without a very, very compelling reason for overriding built-in functions, my preference would be to create a new function that cannot possibly impact usage of a built-in function. -- To reply via email subtract one hundred and four