Functional programming language in the context of First-class object

In software, control flow (or flow of control) describes how execution progresses from one command to the next. In many contexts, such as machine code and an imperative programming language, control progresses sequentially (to the command located immediately after the currently executing command) except when a command transfers control to another point – in which case the command is classified as a control flow command. Depending on context, other terms are used instead of command. For example, in machine code, the typical term is instruction and in an imperative language, the typical term is statement.

Although an imperative language encodes control flow explicitly, languages of other programming paradigms are less focused on control flow. A declarative language specifies desired results without prescribing an order of operations. A functional language uses both language constructs and functions to control flow even though they are usually not called control flow statements.

In computer programming, an anonymous function (function literal, lambda function, or block) is a function definition that is not bound to an identifier. Anonymous functions are often arguments being passed to higher-order functions or used for constructing the result of a higher-order function that needs to return a function.If the function is only used once, or a limited number of times, an anonymous function may be syntactically lighter than using a named function. Anonymous functions are ubiquitous in functional programming languages and other languages with first-class functions, where they fulfil the same role for the function type as literals do for other data types.

Anonymous functions originate in the work of Alonzo Church in his invention of the lambda calculus, in which all functions are anonymous, in 1936, before electronic computers. In several programming languages, anonymous functions are introduced using the keyword lambda, and anonymous functions are often referred to as lambdas or lambda abstractions. Anonymous functions have been a feature of programming languages since Lisp in 1958, and a growing number of modern programming languages support anonymous functions.