Go: functions as first-class objects, variadic functions and generics

faafco.go

package main

import "fmt"

func plus[T int | float32](i1 T, i2 T) T {
	return i1 + i2
}

func minus[T int | float32](i1 T, i2 T) T {
	return i1 - i2
}

func variade[T int | float32](f func(T, T) T, args ...T) T {
	if args == nil {
		panic("Not enough arguments")
	}
	if len(args) == 2 {
		return f(args[0], args[1])
	}
	// This would be wrong, cause subtraction is not associative:
	// return f(args[0], variade(f, args[1:]...))
	return variade(f, append([]T{f(args[0], args[1])}, args[2:]...)...)
}

func main() {
	fmt.Println(float32(variade(minus[int], 100, 90, 9)))
	// Prints 7.6
	fmt.Println(variade(plus[float32], 1.1, 2.2, 3.3, float32(variade(minus[int], 100, 90, 9))))
}