first_class_function.go

package main

import (
	"fmt"
	"math"
)

type Calculator struct {
        acc float64
}

type OP func(v float64) float64

func (c *Calculator) Do(op OP) float64 {
       c.acc = op(c.acc)
       return c.acc
}

func add(v float64) OP{
	return func(vv float64) float64 {
		return v + vv
	}
}

func sub(v float64) OP{
	return func(vv float64) float64 {
		return vv - v
	}
}
func squre(_ float64) OP{
	return func(vv float64) float64 {
		return vv * vv
	}
}
func main() {
	var c Calculator
       fmt.Println(c.Do(add(100)))	
	fmt.Println(c.Do(sub(50)))	
	fmt.Println(c.Do(squre(0)))	
	fmt.Println(c.Do(math.Sqrt))		
}