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eintr: Primitive Functions

 
 An Aside about Primitive Functions
 ==================================
 
 All functions are defined in terms of other functions, except for a few
 “primitive” functions that are written in the C programming language.
 When you write functions’ definitions, you will write them in Emacs Lisp
 and use other functions as your building blocks.  Some of the functions
 you will use will themselves be written in Emacs Lisp (perhaps by you)
 and some will be primitives written in C.  The primitive functions are
 used exactly like those written in Emacs Lisp and behave like them.
 They are written in C so we can easily run GNU Emacs on any computer
 that has sufficient power and can run C.
 
    Let me re-emphasize this: when you write code in Emacs Lisp, you do
 not distinguish between the use of functions written in C and the use of
 functions written in Emacs Lisp.  The difference is irrelevant.  I
 mention the distinction only because it is interesting to know.  Indeed,
 unless you investigate, you won’t know whether an already-written
 function is written in Emacs Lisp or C.
 

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