Re: Pattern to match a list of non-negative integers

*To*: mathgroup at smc.vnet.net*Subject*: [mg108934] Re: Pattern to match a list of non-negative integers*From*: David Bailey <dave at removedbailey.co.uk>*Date*: Wed, 7 Apr 2010 07:25:52 -0400 (EDT)*References*: <hphbnd$lj5$1@smc.vnet.net>

Leo Alekseyev wrote: > This seems like a very basic pattern-matching question, but somehow > the answer eludes me at the moment. I want to match a list of > non-negative integers. Something like MatchQ[{1,2},{(x_Integer /; x >> = 0)..}] doesn't work -- do named patterns simply not play well with > Repeated[]?.. > > After starting to write this message, the following pattern, occurred to me: > MatchQ[{2, 3}, x : {_Integer ..} /; ! MemberQ[x, y_ /; Negative[y]]] > -- this works, but seems needlessly complex -- so I'll send the > message on, in hopes that there is a cleaner way of writing the > pattern. > Well probably the neatest solution is to write a test suitableListQ that checks the list out and returns True or False, and then write: x_?suitableListQ This is of course, extremely general. BTW, In time critical code, I tend to avoid complex patterns, because I find their performance can be a bit unpredictable. David Bailey http://www.dbaileyconsultancy.co.uk