Definitions

Traits often considered important for constituting a programming language:

• Function: A programming language is a language used to write computer programs, which involve a computer performing some kind of computation^[4] or algorithm and possibly control external devices such as printers, robots,^[5] and so on.

• Target: Programming languages differ from natural languages in that natural languages are only used for interaction between people, while programming languages also allow humans to communicate instructions to machines. Some programming languages are used by one device to control another. For example PostScript programs are frequently created by another program to control a computer printer or display.

• Constructs: Programming languages may contain constructs for defining and manipulating data structures or controlling the flow of execution.

• Expressive power: The theory of computation classifies languages by the computations they can express (see Chomsky hierarchy). All Turing complete languages can implement the same set of algorithms. ANSI/ISO SQL and Charity are examples of languages that are not Turing complete yet often called programming languages.^[6][7]

Non-computational languages, such as markup languages like HTML or formal grammars like BNF, are usually not considered programming languages. Often a programming language is embedded in the non-computational (host) language.