Suppressing part of error message output

Questions
,
1

If I have a simple function definition such as:

f::badargs = "A single argument of type integer was expected"; 
f[x_Integer] := x^2; 
f[args___] := "dummyString" /; Message[f::badargs];

Then for non-integer input I get:

In[58]:= f[.2] 
During evaluation of In[58]:= f::badargs: A single argument of type integer was expected 
Out[58]= f[0.2]

Is there a way to print the message, but prevent the f[0.2] from printing? I’m using a similar approach for a case where argument is a massive list…that I do not want printed out.
Any help is much appreciated.

2

Two options:
Option 1:

f::badargs = "A single argument of type integer was expected"; 
f[x_Integer] := x^2; 
f[args___] := Message[f::badargs];

Of course, then the unevaluated form isn’t returned. Option 2: Use FormatValues. Something like

In[55]:= f::badargs = "A single argument of type integer was expected"; 
f[x_Integer] := x^2; 
f[args___] := "dummy" /; Message[f::badargs]; 
Format[HoldPattern[f[x : Except[_Integer]]]] := Null; 
Format[HoldPattern[f[]]] := Null; 
Format[HoldPattern[f[_, __]]] := Null 
In[61]:= f[.2] 
During evaluation of In[61]:= f::badargs: A single argument of type 
integer was expected 
Out[61]= Null

doesn’t prevent

In[62]:= HoldForm[f[3]] 
Out[62]= \!\( 
TagBox[ 
RowBox[{"f", "[", "3", "]"}], 
HoldForm]\)

from rendering.

3

There is a serious problem with your implementation that should be pointed out: you put the Message call into a pattern test. This means that Message[] may get evaluated even if the corresponding definition of f[] isn’t.

Suppose that you add the following additional definition to f[]:

f[x_] /; x < 0 := x^3

In this case f[-0.1] will still issue the message.

The correct way to do it is to put Message[] in the body of the function, so it only gets evaluated when the corresponding pattern does match:

f[x_Integer] := x^2f[___] := (Message[f:badarg]; Null)

The Null after Message is not really necessary as Message itself returns Null, but this pattern shows how to control the value being returned.