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Re: How to quote a list of functions?


From: Pascal J. Bourguignon
Subject: Re: How to quote a list of functions?
Date: Thu, 13 Aug 2015 06:20:12 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)

Emanuel Berg <address@hidden> writes:

> Barry Margolin <address@hidden> writes:
>
>>> And those are, besides checking if there is such
>>> a function?
>>
>> Currently that's it, I think. I was just describing
>> it in a more generic way.
>
> OK. So it should look like this:
>
> (put #'upcase-region    'disabled   nil)
> (put #'downcase-region  'disabled   nil)
> (put #'erase-buffer     'disabled   nil)
> (put #'suspend-frame    'disabled   t  )

Definitely not.

The notion of type should still exist in the mind of the programmer, if
not in the compiler!

The first parameter of put is of type symbol
(function x) returns an object of type function.
While it's true that in emacs lisp, symbol is a subtype of function,
the reverse is not true.  Some functions are not symbols.
Therefore, the Lyskoff Substitution Principle tells us that 

   (put #'upcase-region    'disabled   nil)

is a gross error.  It should be:

   (put 'upcase-region    'disabled   nil)

-- 
__Pascal Bourguignon__                 http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
dog. The man will be there to feed the dog. The dog will be there to
keep the man from touching the equipment.” -- Carl Bass CEO Autodesk


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