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MathGroup Archive 2007

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Re: Function as an argument

  • To: mathgroup at smc.vnet.net
  • Subject: [mg76751] Re: Function as an argument
  • From: Bill Rowe <readnewsciv at sbcglobal.net>
  • Date: Sat, 26 May 2007 04:52:33 -0400 (EDT)

On 5/25/07 at 6:20 AM, dxdydzdu at gmail.com (dXdYdZdu) wrote:

>Hi, I have problem. I want to do something like this:
>
>ss[x_] = 2 + x^3 ; MyFunction[expression_] := Module[{},
>Return[expression[2]]]

>Calling MyFunction[ss] will produce 10 and this is working case.

>but this is what I can not do:

>MyFunction[2 + x^3]

>Is there a way to make this to work as well?

Yes, instead of writing an expression with an explicitly named
variable write it as a pure function, i.e., as you wrote
MyFunction this works

In[16]:= MyFunction[2 + #^3 &]

Out[16]= 10

There are other alternatives, for example

In[17]:= Clear[MyFunction];
MyFunction[expression_, var_: x] := expression /. var -> 2

In[19]:= MyFunction[2 + x^3]

Out[19]= 10

and note this version does the right thing even if you use a
different variable name, i.e.,

In[20]:= MyFunction[2 + y^3, y]

Out[20]= 10

Note, since you aren't using local variables and have no code to
execute after expression is evaluated neither Module nor Return
are needed. That is your design could be written as

MyFunction[expression_] := expression[2]
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