Re: [Q] Extracting patterns

*To*: mathgroup at smc.vnet.net*Subject*: [mg18667] Re: [mg18607] [Q] Extracting patterns*From*: "Andrzej Kozlowski" <andrzej at tuins.ac.jp>*Date*: Thu, 15 Jul 1999 01:45:52 -0400*Sender*: owner-wri-mathgroup at wolfram.com

You were nearly there. The correct function is not HoldPattern but Verbatim In[5]:= Pattern[x, y] /. Verbatim[Pattern[a_, b_] ] -> a Out[5]= x:y In[6]:= FullForm[%] Out[6]//FullForm= Pattern[x, y] -- Andrzej Kozlowski Toyama International University JAPAN http://sigma.tuins.ac.jp http://eri2.tuins.ac.jp ---------- >From: "Kevin Jaffe" <kj0 at mailcity.com> To: mathgroup at smc.vnet.net >To: mathgroup at smc.vnet.net >Subject: [mg18667] [mg18607] [Q] Extracting patterns >Date: Tue, Jul 13, 1999, 2:01 PM > > > > How can I extract the first argument of expressions having the form > Pattern[x, y]? I know how to do something like this in other > situations, e.g.: > > > In[1]:= Plus[x, y] /. Plus[a_, b_] -> a > > Out[1]= x > > > But this strategy fails when the head of the lhs expression is Pattern: > > In[2]:= Pattern[x, y] /. Pattern[a_, b_] -> a > > Pattern::patsym: First element in pattern Pattern[a_, b_] is not a symbol. > > Out[2]= x:y > > > In a last-gasp effort, I also tried: > > In[3]:= Pattern[x, y] /. HoldPattern[Pattern[a_, b_]] -> a > > Pattern::patsym: First element in pattern Pattern[a_, b_] is not a symbol. > > Out[3]= x:y > > to no avail. Is there a way to do this? > > Thanks, > > kj0 at mailcity.com > > > > Get your FREE Email at http://mailcity.lycos.com > Get your PERSONALIZED START PAGE at http://my.lycos.com