package parse

// TokenKind is a number identifying a token kind. To enumerate your set of
// tokens, use iota and start at zero.
type TokenKind int; const (
	EOF TokenKind = -1
)

// Token is any token.
type Token struct {
	Position Position
	Kind     TokenKind
	Value    string
}

// EOF returns whether or not the token is an EOF token.
func (tok Token) EOF () bool {
	return tok.Kind == EOF
}

// Is returns whether or not the token kind matches any of the given kinds.
func (tok Token) Is (kinds ...TokenKind) bool {
	for _, kind := range kinds {
		if tok.Kind == kind { return true }
	}
	return false
}

// Is returns whether or not the token value matches any of the given values.
func (tok Token) ValueIs (values ...string) bool {
	for _, value := range values {
		if tok.Value == value { return true }
	}
	return false
}

// Lexer is an object capable of producing tokens.
type Lexer interface {
	// Next returns the next token. If there are no more tokens, it returns
	// an EOF token. It only returns an error on EOF if the file terminated
	// unexpectedly.
	Next () (Token, error)
}