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RE: Checking if a function is built-in

From: Drew Adams
Subject: RE: Checking if a function is built-in
Date: Tue, 10 Jun 2008 15:51:05 -0700

> > > Is there a predicate that can check if a function is built-in?
> >
> > subrp
> I thought this was the way to use it (subrp 'cons)
> but it returns nil even though cons is a built-in function.
> Have I missed something?

(subrp (symbol-function 'cons))

`cons' is just a symbol. What you want to test is the function that the symbol
refers to. 

This is not the value of the symbol but the value of its function cell, which is
a function (a subr, in this case).

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