Computer Science › Compilers & Languages
Programming Paradigms
Styles of programming: imperative, object-oriented, functional, declarative.
Also known as: programming paradigms, paradigm, imperative, object-oriented, functional
A programming paradigm is a style, or way of thinking, about how to structure a program. Most languages support several, and real code mixes them.
| Paradigm | Core idea | Examples |
|---|---|---|
| Imperative / procedural | a sequence of commands that change state, organized into procedures | C, shell scripts, much everyday Python |
| Object-oriented | objects bundle data and behavior, and communicate by calling methods (OOP) | Java, C#, Python, Ruby |
| Functional | build programs from functions that avoid shared mutable state (functional programming) | Haskell, Elixir, and parts of JavaScript and Python |
| Declarative | describe the result you want, and let the system work out how (declarative vs imperative) | SQL, HTML, configuration files |
| Event-driven / reactive | the flow is controlled by events and callbacks | UI code, Node.js servers |
| Logic | state facts and rules, and let an engine search for answers | Prolog |
# The same task in two styles
total = 0
for n in nums: # imperative
if n % 2 == 0:
total += n
total = sum(n for n in nums if n % 2 == 0) # functional/declarative flavorWhy learn about them
- They give you more tools. Some problems fit objects, some fit data transformation, some fit rules.
- You can read more code. Frameworks lean on a style: React is functional and declarative, Java frameworks are object-oriented.
- Languages differ in what they encourage, and understanding the paradigm explains the language’s idioms.
Don’t be dogmatic
No paradigm is best. Modern languages are multi-paradigm, and good engineers choose the style that suits each part: a pure functional core, objects at the boundaries, declarative queries for data. Learn the ideas, and let the problem decide.