Re: bug when 'p' fails to evaluate?

*To*: mathgroup at smc.vnet.net*Subject*: [mg115776] Re: bug when 'p' fails to evaluate?*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Thu, 20 Jan 2011 06:31:37 -0500 (EST)

On 1/19/11 at 5:29 AM, lehin.p at gmail.com (Alexey) wrote: >I wonder why treats Sort[...,p] unevaluated comparison function 'p' >as if it was evaluated to True. Is it a bug? >In[1]:= Sort[{a, c, d}, True &] Sort[{a, c, d}, UndefinedFunction &] >Sort[{a, c, d}, Greater] >Out[1]= {a, c, d} >Out[2]= {a, c, d} >Out[3]= {a, c, d} >I think the expected behavior should be to return unevaluated >Sort[...]. Since Sort should do nothing more than change the order of elements of a list, it seems to me to be perfectly reasonable for Sort to return the list with the element order unchanged when it isn't possible to make meaningful comparisons of one element with another. In fact, I see no advantage to putting what would amount to a wrapper on the original list if meaningful comparisons cannot be made.