Re: Re: Taking either a sequence or a list

*To*: mathgroup at smc.vnet.net*Subject*: [mg63398] Re: [mg63318] Re: Taking either a sequence or a list*From*: "Oyvind Tafjord" <tafjord at wolfram.com>*Date*: Thu, 29 Dec 2005 02:57:29 -0500 (EST)*References*: <dnm29m$89q$1@smc.vnet.net> <dnopf9$2gp$1@smc.vnet.net> <dnrd16$kqf$1@smc.vnet.net> <200512231008.FAA25950@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

----- Original Message ----- From: "Maxim" <m.r at inbox.ru> To: mathgroup at smc.vnet.net Subject: [mg63398] [mg63318] Re: Taking either a sequence or a list >> >> This definitely looks like an inconsistency: >> >> In[1]:= MatchQ[{a}, {__Integer | a}] >> >> Out[1]= True >> >> In[2]:= MatchQ[{a}, {x : __Integer | a}] >> >> Out[2]= False This is a known issue (inconsistent handling of Alternatives) which is fixed in future versions. >> >> It is also unclear exactly what value is assigned to x here: >> >> In[4]:= tmp = {a} /. {x : __} -> x >> >> Out[4]= a >> >> In[5]:= tmp2 = {a} /. {x : __ | __} -> x >> >> Out[5]= Sequence[a] The result should be "a" in both cases (don't wrap Sequence around single-element sequences), fixed in future versions (by the same fix as the above). >> > > Here's another curious inconsistency: > > In[1]:= MatchQ[{a, a}, {s_, s_} /; True /; False] > > Out[1]= False > > In[2]:= MatchQ[{a, a}, {s__, s__} /; True /; False] > > Out[2]= True This is a bug I haven't seen before, involving nested Conditions/PatternTests surrounding "non-unique" patterns. Will be fixed in future versions. Thanks for pointing it out. Oyvind Tafjord Wolfram Research > > Perhaps Mathematica takes some shortcuts when dealing with patterns that > require a combinatorial search (sequences or Orderless/Flat functions), > but such 'simplified' handling of certain classes of patterns can produce > rather strange results. > > Maxim Rytin > m.r at inbox.ru

**References**:**Re: Taking either a sequence or a list***From:*Maxim <m.r@inbox.ru>