lstinsert0

lstinsert0 is a naming convention used in some programming libraries to describe the operation of inserting an element at the head of a list, i.e., at index 0. The exact implementation and side effects depend on whether the list is immutable or mutable, and on the underlying data structure (such as a linked list versus a dynamic array).

In immutable-list contexts, lstinsert0(element, list) returns a new list with the element prepended to the front, leaving the original list unchanged. In mutable contexts, the operation may modify the existing list in place to place the new element at the front. The term emphasizes the position rather than the method of insertion.

Common signatures and interpretations vary by language:

- Lisp/Scheme: (lstinsert0 element lst) typically results in (cons element lst).

- Python: lstinsert0 = lambda elem, lst: [elem] + lst, producing a new list with elem at the front.

- JavaScript: function lstinsert0(elem, lst) { return [elem].concat(lst); }.

- C for a singly linked list: a function that allocates a new node with data = elem and next = lst, returning the new head.

- Haskell: element : list, where the colon operator prepends an element.

Complexity and implications: for linked-list implementations, inserting at the head is O(1). For array-backed lists that create a new structure, the operation can be O(n) due to copying. In languages with immutable data, lstinsert0 inherently creates a new list; in mutable scenarios, it may simply adjust a pointer.

See also: prepend, cons, push_front, and zero-based indexing.