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Re: HoldAll/HoldRest

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  Re: HoldAll/HoldRest Albert Retey <awnl@gmx-topmail.de> - 2011-04-30 09:53 +0000

#1929 — Re: HoldAll/HoldRest

Hi,

> Some kind of issue going on here between the interactions of HoldAll
> of ValueQ[...] and HoldRest of If[...]. Anyone know the solution so
> that Out[3] results in True?

It's Function which evaluates its arguments by default, you can do:

valueQ = Function[Null, If[ValueQ[#], #, False], HoldAll]

to avoid that.

> = = In[1]:= valueQ = If[ValueQ[#], #,
> False]& =
>
> = Out[1]= If[ValueQ[#1], #1, False]& =
>
> = In[2]:= x = 5 =
>
> = Out[2]= 5 =
>
> = In[3]:= valueQ[5] =
>
> = Out[3]= False

I guess that should be valueQ[x], otherwise you shouldn't wonder about 
the result...

hth,

albert

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