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How to calculate the difference between two sets in Emacs Lisp? The sets should be lists. The programm should be very simple and short, or else I won't understand it. I'm a newbee.
Thx
398
#'... is short-hand for (function ...) which is simply a variant of '... / (quote ...) that also hints to the byte-compiler that it can compile the quoted form as a function.
In a fresh Emacs window, type ESC-x lisp-interaction-mode . That will turn your buffer into a LISP terminal; pressing Ctrl+j will feed the s-expression that your cursor (called "point" in Emacs manuals' jargon) stands right behind to LISP, and will print the result.
Emacs Lisp has a compiler that translates functions written in Lisp into a special representation called byte-code that can be executed more efficiently. The compiler replaces Lisp function definitions with byte-code. When a byte-code function is called, its definition is evaluated by the byte-code interpreter.
Emacs Lisp supports multiple programming styles or paradigms, including functional and object-oriented. Emacs Lisp is not a purely functional programming language since side effects are common. Instead, Emacs Lisp is considered an early functional flavored language.
There is a set-difference function in the Common Lisp extensions:
elisp> (require 'cl-lib)
cl-lib
elisp> (cl-set-difference '(1 2 3) '(2 3 4))
(1)
When I write Elisp code that has lots of list data transformations, I use dash library, because it has loads of functions to work with lists. Set difference can be done with -difference:
(require 'dash)
(-difference '(1 2 3 4) '(3 4 5 6)) ;; => '(1 2)
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