Example of currying (higher order functions) in Go

curry.go

package main

import "fmt"

type List struct {
        Inner []int
}   

func NewList(s []int) List {
        return List{Inner: s}
}

func (li List) Map(fn func(int) int) (List) {
        out := []int{}
        for _, num := range li.Inner {
                num = fn(num)
                out = append(out, num)
        }       
        return List{Inner: out}
}       

func main() {
        multiply := func(a int) (func(int) int) {
		return func(b int) int {
			return a * b
		}
	}
        
        fmt.Println(multiply(2)(3))   // 6
        
        nums := []int{1, 3, 5, 9}
        li := NewList(nums)
        list1 := li.Map(multiply(2))
        list2 := li.Map(multiply(10))
        
        fmt.Println(list1)   // [2, 6, 5, 9]
        fmt.Println(list2)   // [10, 30, 50, 90]
}