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MathGroup Archive 1997

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Overloading mathematica built in functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg5716] Overloading mathematica built in functions
  • From: seanross at worldnet.att.net
  • Date: Sat, 11 Jan 1997 14:29:10 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

I want to add a capability to the Sum function.  If I give it a 
single argument that is a 1-D list, I want it to sum the list. For 
example:

In[1]:=
w={1,1,1,3};
Sum[w]
Out[1]:=
5

The function
sum[f_List]:=Sum[f[[i]],{i,1,Length[f]}];
performs this function, However

Unprotect[Sum];
Sum[f_List]:=Sum[f[[i]],{i,1,Length[f]}];
Protect[Sum];

does not work.  Does anyone know why?  I am guessing it has something to 
do with the attribute HoldAll on the built-in function Sum.  Is there a 
way to overload a function so that the attributes are different for 
different argument lists?  

Thanks


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