Bug in pattern matching?

*To*: mathgroup at smc.vnet.net*Subject*: [mg8722] Bug in pattern matching?*From*: "Peter Strömbeck" <pqst at celsiustech.se>*Date*: Fri, 19 Sep 1997 02:48:02 -0400*Organization*: CelsiusTech Electronics AB*Sender*: owner-wri-mathgroup at wolfram.com

Hi, I've posted this problem to Wolfram support but received no answer so I thought I might just post it here aswell. I'm trying to "deconstruct" a list, perform an operation to a pert of the list and then recombine the result. When I did this I found out that multiplication in pattern matching performs differently than otherwise. Check version: In[1]:= $Version Out[1]= "Microsoft Windows 3.0 (October 6, 1996)" Define list: In[2]:= ls=Table[a[j], {j,0,5}] Out[2]= {a[0],a[1],a[2],a[3],a[4],a[5]} I want to split this list into the following three sublists: {a[0],a[1],a[2],a[3],a[4],a[5]} -> {a[0]}, {a[1], a[2], a[3], a[4]}, {a[5]} Use pattern matching: In[3]:= ls/.{first_, middle___, last_}\[Rule] {{first},{middle},{last}} Out[3]= {{a[0]},{a[1],a[2],a[3],a[4]},{a[5]}} This works fine. Now I want to multiply the middle list by a factor C. Ordinary multiplication works like this: In[4]:= C ls Out[4]= {C a[0],C a[1],C a[2],C a[3],C a[4],C a[5]} Doing this in a pattern matching statement produces a totally different result: In[5]:= ls/.{first_, middle___, last_}\[Rule] {{first},C {middle},{last}} Out[5]= {{a[0]},{C a[1] a[2] a[3] a[4]},{a[5]}} The middle list now contains a completely different result than Out[4]! Can anyone please explain this to me? /Peter Strömbeck