In** computer programming, **** **** is the operation for concatenating linked lists or arrays in some high-level programming **languages.

Lisp

originates in the programming language Lisp. The procedure takes zero or more (linked) lists as arguments, and returns the concatenation of these lists. Since the 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. The procedure (called in Scheme) performs the same function as , but destructively: it alters the cdr of each argument (save the last), pointing it to the next list.

Implementation

can easily be defined recursively in terms of. The following is a simple implementation in Scheme, for two arguments only: Append can also be implemented using fold-right:

Other languages

Following Lisp, other high-level programming languages which feature linked lists as primitive data structures have adopted an. To append lists, as an operator, Haskell uses, OCaml uses. Other languages use the or symbols to nondestructively concatenate a string, list, or array.

Prolog

The logic programming language Prolog features a built-in predicate, which can be implemented as follows: This predicate can be used for appending, but also for picking lists apart. Calling yields the solutions: L = [], R = [1, 2, 3] ; L = [1], R = [2, 3] ; L = [1, 2], R = [3] ; L = [1, 2, 3], R = []

Miranda

In Miranda, this right-fold, from Hughes (1989:5-6), has the same semantics (by example) as the Scheme implementation above, for two arguments. append a b = reduce cons b a Where reduce is Miranda's name for fold, and cons constructs a list from two values or lists. For example, append [1,2] [3,4] = reduce cons [3,4] [1,2] = (reduce cons [3,4]) (cons 1 (cons 2 nil)) = cons 1 (cons 2 [3,4])) (replacing cons by cons and nil by [3,4]) = [1,2,3,4]

Haskell

In Haskell, this right-fold has the same effect as the Scheme implementation above: This is essentially a reimplementation of Haskell's operator.

Perl

In Perl, the push function is equivalent to the append method, and can be used in the following way. The end result is a list containing [1, 2, 3] The unshift function appends to the front of a list, rather than the end The end result is a list containing [2, 3, 1] When opening a file, use the ">>" mode to append rather than over write. Note that when opening and closing file handles, one should always check the return value.

Python

In Python, use the list method extend or the infix operators + and += to append lists. Do not confuse with the list method append, which adds a single element to a list:

Bash

In Bash the append redirect is the usage of ">>" for adding a stream to something, like in the following series of shell commands: The stream "Goodbye world!" is added to the text file written in the first command. The ";" implies the execution of the given commands in order, not simultaneously. So, the final content of the text file is: