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Question on Unevaluated

• To: mathgroup at smc.vnet.net
• Subject: [mg117264] Question on Unevaluated
• From: Alexey <lehin.p at gmail.com>
• Date: Sun, 13 Mar 2011 05:26:42 -0500 (EST)

Hello,

I am puzzled a bit by the Documentation for Unevaluated. Under "More
information" field we read:

"f[Unevaluated[expr]] effectively works by temporarily setting
attributes so that f holds its argument unevaluated, then evaluating
f[expr].".

After reading this I expect that

f[Unevaluated[1 + 1]; 2 + 1]

will be returned completely unevaluated as it is when I set HoldFirst
attribute to f:

In[2]:= SetAttributes[f, HoldFirst]
f[Unevaluated[1 + 1]; 2 + 1]

Out[3]= f[Unevaluated[1 + 1]; 2 + 1]

But in really we get

In[1]:= f[Unevaluated[1 + 1]; 2 + 1]

Out[1]= f[3]

This leads me to a question: what is implied in documentation? Which
attributes are temporarily set and to which function?

• Follow-Ups:
  • Re: Question on Unevaluated
    • From: Leonid Shifrin <lshifr@gmail.com>