// Package lexer provides basic helpers to implement parsers
package lexer

import (
	"errors"
	"io"
)

// StateFn is a State Function of the parser
type StateFn func() (StateFn, error)

// Run runs a state machine until the state function either
// returns nil or an error
func Run(fn StateFn) error {
	for fn != nil {
		var err error

		fn, err = fn()
		switch {
		case errors.Is(err, io.EOF):
			// EOF
			return nil
		case err != nil:
			// failed
			return err
		}
	}

	// ended
	return nil
}