In computer programming, append is the name of a procedure for concatenating (linked) lists or arrays in some high-level programming languages. Computer code (HTML with JavaScript) in a tool that uses colors to help the developer see the function of each piece of code. ... A procedure is a series of activities, tasks, steps, decisions, calculations and other processes, that when undertaken in the sequence laid down produces the described result, product or outcome. ... In computer science, a linked list is one of the fundamental data structures used in computer programming. ... In computer programming, an array, also known as a vector or list (for one-dimensional arrays) or a matrix (for two-dimensional arrays), is one of the simplest data structures. ... A high-level programming language is a programming language that is easier to program in, to some extent platform-independent, and abstract from low-level computer processor operations such as memory accesses. ...

Lisp

Append originates in the Lisp programming language. The append procedure takes two or more (linked) lists as arguments, and returns the concatenation of these lists. Lisp is a family of computer programming languages with a long history and a distinctive fully-parenthesized syntax. ... In computer science, a linked list is one of the fundamental data structures used in computer programming. ...

 (append '(1 2 3) '(a b) '() '(6)) ;Output: (1 2 3 a b 6) 

Since the append procedure must completely copy all of its arguments except the last, both its time and space complexity are O(n) for a list of n elements. It may thus be a source of inefficiency if used injudiciously in code. In computer science, computational complexity theory is the branch of the theory of computation that studies the resources, or cost, of the computation required to solve a given problem. ... It has been suggested that Landau notation be merged into this article or section. ...

The nconc procedure (called append! in Scheme) performs the same function as append, but destructively: it alters the cdr of each argument (save the last), pointing it to the next list. Scheme is a functional programming language and a dialect of Lisp. ... In computer science, an in-place algorithm is an algorithm which transforms a data structure using a small, constant amount of extra storage space. ... In the Lisp programming language, car and cdr (IPA [kÉ™dÉ™r] or [kudÉ™r]) are a pair of primitive functions to extract the left and right half (respectively) of a cons cell. ...

Implementation

Append can easily be defined in terms of cons. The following is a simple implementation in Scheme, for two arguments only: CONS, Connection-Oriented Network Service, is one of the two OSI stack network layer protocols, the other being CLNS (Connectionless Network Service). ...

 (define (append l1 l2) (if (null? l1) l2 (cons (car l1) (append (cdr l1) l2)))) 

Other languages

Following Lisp, other high-level languages which feature linked lists as primitive data structures have adopted an append. Other languages use the + or ++ symbols for nondestructive string/list/array concatenation. A high-level programming language is a programming language that is more user-friendly, to some extent platform-independent, and abstract from low-level computer processor operations such as memory accesses. ... In computer science, a linked list is one of the fundamental data structures used in computer programming. ... A binary tree, a simple type of branching linked data structure. ... In computer programming and some branches of mathematics, strings are sequences of various simple objects. ...

Prolog

The logic programming language Prolog features a built-in append predicate, which can be implemented as follows: Prolog is a logic programming language. ...

 append([],Ys,Ys). append([X|Xs],Ys,[X|Zs]) :- append(Xs,Ys,Zs). 

This predicate can be used for appending, but also for picking lists apart. Calling

 ?- append(L,R,[1,2,3]). 

yields the solutions:

 L = [], R = [1, 2, 3] ; L = [1], R = [2, 3] ; L = [1, 2], R = [3] ; L = [1, 2, 3], R = [] 

References

Steele, Guy L. Jr. Common Lisp: The Language, Second Edition. 1990. pg. 418, description of append. Common Lisp, commonly abbreviated CL, is a dialect of the Lisp programming language, standardised by ANSI X3. ...