The fox, gopher and bag of beans puzzle in Go -- https://coderwall.com/p/lb3eaw

foxgopher.go

/*
  The fox, gopher and bag of beans puzzle in Go.
  https://coderwall.com/p/lb3eaw
*/
package main

import (
	"fmt"
	"log"
)

//The good 'ol farmer
type Farmer struct {
}

//The gopher (goose) that the farmer purchased at the market
type Gopher struct {
}

func (g *Gopher) Eat(b *BagOfBeans, f *Farmer) {

	if b != nil && f == nil {
		log.Fatal("OOPS: Gopher just ate all the beans")
	}
}

//The bag of beans that the farmer purchased at the market
type BagOfBeans struct {
}

//The fox that the farmer purchased at the market
type Fox struct {
}

func (fox *Fox) Eat(g *Gopher, f *Farmer) {
	if g != nil && f == nil {
		log.Fatal("OOPS: Fox ate gopher just now.")
	}
}

//The boat where the farmer can ride and take only one item with him.
type Boat struct {
	farmer *Farmer
	gopher *Gopher
	fox    *Fox
	beans  *BagOfBeans
}

type Side int

const (
	East = 0
	West = 1
)

type Bank struct {
	farmer *Farmer
	fox    *Fox
	gopher *Gopher
	beans  *BagOfBeans
	side   Side
}

func (b *Bank) checkState() {
	counter := 0
	if b.fox != nil {
		counter++
		b.fox.Eat(b.gopher, b.farmer)
	}

	if b.gopher != nil {
		counter++
		b.gopher.Eat(b.beans, b.farmer)
	}

	if b.beans != nil {
		counter++
	}

	if b.farmer != nil {
		counter++
	}

	sd := "West"
	if b.side == East {
		sd = "East"
	}

	fmt.Printf("%s bank: %+v\n", sd, b)

	if counter == 4 && b.side == West{
		fmt.Println("!!YOU WIN!!")
	}
}

func (b *Bank) Send(boat Boat) {
	b.farmer = nil

	if boat.gopher != nil {
		b.gopher = nil
	}
	if boat.beans != nil {
		b.beans = nil
	}
	if boat.fox != nil {
		b.fox = nil
	}

	b.checkState()
	river <- boat
}

func (b *Bank) Receive() {
	boat := <-river
	b.farmer = boat.farmer

	if boat.gopher != nil {
		b.gopher = boat.gopher
	}
	if boat.beans != nil {
		b.beans = boat.beans
	}
	if boat.fox != nil {
		b.fox = boat.fox
	}

	b.checkState()
}

//The river that the farmer must cross with all his belongings
var river = make(chan Boat, 1)

func main() {
	//The west bank starts off empty
	westBank := Bank{side: West}

	//The east bank starts off with the farmer and his store bought items
	eastBank := Bank{side: East}

	//We create an instance of the farmer, fox, bag of beans, and lastly the gopher
	eastBank.farmer = &Farmer{}
	eastBank.fox = &Fox{}
	eastBank.beans = &BagOfBeans{}
	eastBank.gopher = &Gopher{}


	//ONE SOLUTION IS BELOW

	//Stage 1
	eastBank.Send(Boat{farmer: eastBank.farmer, gopher: eastBank.gopher})
	westBank.Receive()

	//Stage 2
	westBank.Send(Boat{farmer: westBank.farmer})
	eastBank.Receive()

	//Stage 3
	eastBank.Send(Boat{farmer: eastBank.farmer, fox: eastBank.fox})
	westBank.Receive()

	//Stage 4
	westBank.Send(Boat{farmer: westBank.farmer, gopher: westBank.gopher})
	eastBank.Receive()

	//Stage 5
	eastBank.Send(Boat{farmer: eastBank.farmer, beans: eastBank.beans})
	westBank.Receive()

	//Stage 6
	westBank.Send(Boat{farmer: westBank.farmer})
	eastBank.Receive()

	//Stage 7
	eastBank.Send(Boat{farmer: eastBank.farmer, gopher: eastBank.gopher})
	westBank.Receive()

	//var str string
	//fmt.Scanln(&str)
}