goal.go

package main

import (
	"fmt"
)

func main() {
	fmt.Println(g("al"))
	fmt.Println(g()("al"))
	fmt.Println(g()()("al"))
	fmt.Println(g()()()("al"))
	fmt.Println(g()()()()("al"))
	fmt.Println(g()()()()()("al"))
	fmt.Println(g()()()()()()("al"))

	fmt.Println(g()("O")()("O")("al")("!"))
	fmt.Println(g()()("gle"))
	fmt.Println(g()("lang"))
}

type F func(...interface{}) F

func (f F) String() (out string) {
	f(&out)
	return
}

func g(al ...interface{}) F {
	var f F
	out := "g"
	f = func(al ...interface{}) F {
		if len(al) != 1 {
			out += "o"
			return f
		}
		switch a := al[0].(type) {
		case string:
			out += a
		case *string:
			*a = out
		}
		return f
	}
	return f(al...)
}