関数を Go マップに値として保存するにはどうすればよいですか?

import "fmt"

// A function type that takes a string as a parameter.
type StringFunc func(string)

// A map that stores functions that take a string as a parameter.
var funcs map[string]StringFunc

// A function that takes a string as a parameter.
func a(p string) {
    fmt.Println("function a parameter:", p)
}

// Main function.
func main() {
    // Create a map that stores functions that take a string as a parameter.
    funcs = make(map[string]StringFunc)

    // Add the 'a' function to the map.
    funcs["a"] = a

    // Call the 'a' function from the map.
    funcs["a"]("hello")
}