// Package grammar is used for parsing a stream of runes according to a set of
// grammatical rules. This package only supports context-free grammars.
package grammar

import "fmt"

// Stringer is a convenience tool for working with fmt.Stringer. Exactly one of
// the fields must be set, and will be used to implement the fmt.Stringer
// interface.
type Stringer struct {
	I fmt.Stringer
	F func() string
	S string
}

func (s Stringer) String() string {
	switch {
	case s.I != nil:
		return s.I.String()
	case s.F != nil:
		return s.F()
	case s.S != "":
		return s.S
	default:
		panic("no fields set on Stringer")
	}
}