Nonprocedural

Nonprocedural refers to programming approaches that describe what a program should accomplish without prescribing the exact sequence of steps to reach that result. It is often treated as a form of declarative programming, though some authors distinguish nonprocedural as specifically focusing on outcomes and relationships rather than any form of control flow.

Key characteristics include specifying desired outcomes, constraints, or relationships rather than detailing how to manipulate state. A runtime, query processor, or compiler then determines an efficient plan to meet the specification. This often reduces emphasis on side effects and makes reasoning about the code easier in theory, though practical systems may still involve operational details under the hood.

Common examples illustrate the range of nonprocedural styles. SQL expresses what data to retrieve and how data items relate to each other, not the steps to iterate over records. Prolog encodes rules and relationships and answers queries about a knowledge base. HTML and CSS describe document structure and presentation without prescribing procedural rendering steps. Functional languages like Haskell and dataflow or rule-based systems (such as XSLT or SPARQL) emphasize evaluation of expressions or rules over explicit sequences of instructions.

Advantages of nonprocedural approaches include easier maintenance for certain domains, potential for automatic optimization, and improved formal reasoning about programs. Limitations involve possible inefficiencies, difficulties in expressing certain algorithms naturally, and a learning curve. In practice, many languages blend procedural and nonprocedural features, offering both explicit control and high-level declarative constructs.