In
computer science,
imperative programming is a
programming paradigm that describes computation in terms of
statements that change a program
state. In much the same way that
imperative mood in
natural languages expresses commands to take action, imperative programs define sequences of commands for the computer to perform.
The term is used in opposition to declarative programming, which expresses what needs to be done, without prescribing how to do it in terms of sequences of actions to be taken. Functional and logical programming are examples of a more declarative approach.
Procedural programming could be considered as a step towards declarative programming. A programmer can often tell, simply by looking at the names, arguments and return types of procedures (and related comments), what a particular procedure is supposed to do - without necessarily looking at the detail of how the procedure achieves its result. At the same time, a complete program is still imperative since it 'fixes' the statements to be executed and their order of execution to a large extent.
In a pure functional language, such as Haskell, all functions are without side effects, and state changes are only represented as functions that transform the state. Although pure functional languages are non-imperative, they often provide a facility for describing the effect of a function as a series of steps. Other functional languages, such as Lisp, OCaml and Erlang, support a mixture of procedural and functional programming.
