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MathGroup Archive 2000

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Re: Test for On/Off

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24710] Re: [mg24689] Test for On/Off
  • From: Adalbert Hanssen <hanssen at Zeiss.de>
  • Date: Wed, 9 Aug 2000 02:31:09 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi, All!

If you say Off[message], then the message is wrapped in $Off:

In[13]:=On[General::spell]
In[14]:=General::spell
Out[14]="Possible spelling error: new symbol name \"`1`\" is 
        similar to existing symbols `2`."

In[15]:=Off[General::spell]
In[16]:=General::spell
Out[16]=$Off["Possible spelling error: new symbol name \"`1`\" 
        is similar to existing symbols `2`."]

In order to determine the On/Off state, we can investigate the 
Head of the message:

In[17]:=On[General::spell]
In[18]:=Head[General::spell]
Out[18]=String

In[19]:=Off[General::spell]
In[20]:=Head[General::spell]
Out[20]=$Off

The message is Off, if the head of it is $Off. An implementation 
of checking the current state would be:

In[43]:=
CurrentState[message_]:=If[Head[Evaluate[message]]===$Off
                          ,Off
                          ,On
                          ];
Attributes[CurrentState]={HoldAll};

In[46]:=On[General::spell];
        CurrentState[General::spell]
        Off[General::spell];
        CurrentState[General::spell]
Out[47]=On
Out[49]=Off


Now, I would like to overload On[message] and Off[message], such 
that they always return the previous state before On and Off were 
applied. Any Idea how to overload On and Off?

Regards

Adalbert


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