What functional programming languages ​​are there?

Functional programming language is a programming paradigm whose core idea is to treat calculations as operations on functions. Functional programming languages ​​are different from traditional imperative programming languages. They emphasize minimizing the state and variability of the program and realizing program functions by converting and combining data. Several common functional programming languages ​​will be introduced below, with corresponding code examples.

1. Haskell:
   Haskell is a strongly statically typed purely functional programming language with lazy evaluation characteristics. Its code example is as follows:

-- 求阶乘
factorial :: Integer -> Integer
factorial 0 = 1
factorial n = n * factorial (n - 1)

main :: IO ()
main = do
  putStrLn "请输入一个正整数："
  n <- readLn
  putStrLn ("阶乘结果为：" ++ show (factorial n))

2. Lisp:
   Lisp is one of the earliest functional programming languages. It uses S-expressions to represent code and data and allows functions to be passed as arguments. Here is a simple Lisp example:

; 定义阶乘函数
(defun factorial (n)
  (if (<= n 1)
      1
      (* n (factorial (- n 1)))))

; 调用阶乘函数
(print (factorial 5))

3. Clojure:
   Clojure is a Lisp-based functional programming language that runs on the Java Virtual Machine and provides Concurrent programming support. Here is an example from Clojure:

; 定义阶乘函数
(defn factorial [n]
  (if (<= n 1)
      1
      (* n (factorial (- n 1)))))

; 调用阶乘函数
(println (factorial 5))

4. Erlang:
   Erlang is a concurrent programming language that is widely used in the development of high-availability systems. Here is an example in Erlang:

% 定义阶乘函数
factorial(0) -> 1;
factorial(N) -> N * factorial(N - 1).

% 调用阶乘函数
io:format("~p~n", [factorial(5)]).

5. Swift:
   Swift is a modern multi-paradigm programming language that supports functional programming. The following is a Swift example:

// 定义阶乘函数
func factorial(_ n: Int) -> Int {
  if n <= 1 {
    return 1
  }
  return n * factorial(n - 1)
}

// 调用阶乘函数
let result = factorial(5)
print(result)

The above are code examples for several common functional programming languages. Through these examples, we can learn about the syntax and features of different functional programming languages ​​and how to use them to implement a functional programming style. Of course, in addition to the functional programming languages ​​mentioned above, there are many other languages ​​that also support or partially support functional programming, such as Python, JavaScript, etc.

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