How can I hide $Aborted message?

I know that I'm aborting the evaluation and can see it when the black bar on the side开发者_高级运维 goes away. So there is no need for this message. How do I turn it off?

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The following is a generalization of the $Pre-based method suggested by Simon and the $Post-based method suggested by Mr.Wizard.

In both cases one should set HoldAllComplete attribute to the pure functions and wrap x (input expression) inside them by Unevaluated so they work correctly with inputs having Heads Sequence, Unevaluated and Evaluate.

Compare two versions of the $Pre-based solution:

f1 = Function[{x}, CheckAbort[x, Null], {HoldAll}]
f2 = Function[{x}, CheckAbort[Unevaluated@x, Null], {HoldAllComplete}]

In[3]:= f1@Sequence[1,2]
f1@Abort[]
f1@Evaluate[Abort[]]
f1@Unevaluated[1+1]
Out[3]= 1
Out[5]= $Aborted
Out[6]= 2

In[7]:= f2@Sequence[1,2]
f2@Evaluate[Abort[]]
f2@Unevaluated[1+1]
Out[7]= Sequence[1,2]
Out[9]= Unevaluated[1+1]

One can see that the first version can easily be broken with Evaluate[Abort[]] and works incorrectly with input expressions having Heads Sequence and Unevaluated. It is generally true for any one-argument function without HoldAllComplete attribute. Since $Pre, $Post and friends all are one-argument functions one must always set HoldAllComplete attribute to them.

I also see no problems with using Null as the second argument of CheckAbort (there is no need for Return@Null). On my machine (Mathematica 7.0.1 under Windows 2000) $Abort is never returned in the case of the f2.

The same is true for the $Post-based solution. It can be generalized as follows:

$Post = Function[x, If[Unevaluated@x =!= $Aborted, Unevaluated@x], 
  HoldAllComplete]

Test expressions:

In[14]:= Unevaluated[1+2]
Sequence[1,2]
$Aborted
Abort[]
Out[14]= Unevaluated[1+2]
Out[15]= Sequence[1,2]

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If you are not using $Post for something else, or if you can combine functions, you could use:

$Post = # /. $Aborted -> Null &;

Be warned that you may break things, as programs may use $Aborted in their control flow.

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More robustly, addressing the problem Alexey demonstrates:

$Post = Function[Null, Unevaluated@# /. $Aborted -> Null, HoldAllComplete];

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The following seems to work:

SetAttributes[katch, HoldAll];
katch[x_] := CheckAbort[x, Return@Null] 
$Pre = katch;

After testing, remember to return $Pre to its previous value:

$Pre =.

Probably interferes with some internal abort catching, though.

Edit

Simon's version:

$Pre = Function[{x}, CheckAbort[x,Return@Null], {HoldAll}]