A variable defaulting to a previous variable?

*To*: mathgroup at smc.vnet.net*Subject*: [mg121920] A variable defaulting to a previous variable?*From*: Brentt <brenttnewman at gmail.com>*Date*: Thu, 6 Oct 2011 04:25:54 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

How would one go about making a variable default to a previous variable? I would like results like this: In[1]= f[x_, y_: x] := x+y; > In[2]= f[2,3] > Out[1]= 5 > In[3]= f[3] > Out[1]= 6 > But, of course, Mathematica won't let me use a previous argument for the default of the next argument. Is there a way to do this?

**Follow-Ups**:**Re: A variable defaulting to a previous variable?***From:*Leonid Shifrin <lshifr@gmail.com>

**Re: A variable defaulting to a previous variable?***From:*DrMajorBob <btreat1@austin.rr.com>