In Go, functions are first-class citizens. This means they can be assigned to variables, passed as arguments to other functions, and returned from functions. Higher-order functions are functions that take other functions as parameters or return functions.

first-class_and_higher-order_functions.go

package main

import (
	"fmt"
)

// Define some basic arithmetic operations as first-class functions.
// These functions can be assigned to variables, passed as arguments, and returned from other functions.
var sum = func(a, b int) int { return a + b }
var minus = func(a, b int) int { return a - b }
var multiply = func(a, b int) int { return a * b }
var divide = func(a, b int) int { return a / b }

// Higher-order function: 'calculation' takes another function 'do' as an argument.
// This demonstrates how functions can be passed as parameters to other functions.
func calculation(do func(int, int) int, a, b int) int {
	return do(a, b)
}

func main() {
	a := 10
	b := 2

	// Using the higher-order function 'calculation' with different operations.
	// This showcases the flexibility and reusability of functional programming.
	fmt.Printf("sum: %d\n", calculation(sum, a, b))
	fmt.Printf("minus: %d\n", calculation(minus, a, b))
	fmt.Printf("multiply: %d\n", calculation(multiply, a, b))
	fmt.Printf("divide: %d\n", calculation(divide, a, b))
}

// Output:
// sum: 12
// minus: 8
// multiply: 20
// divide: 5