s.nlsemi = true
		s.tok = _Rbrace

	case ':':
		s.nextch()
		if s.ch == '=' {
			s.nextch()
			s.tok = _Define
			break
		}
		s.tok = _Colon

	case '.':
		s.nextch()
		if isDecimal(s.ch) {
			s.number(true)
			break
		}
		if s.ch == '.' {
			s.nextch()
			if s.ch == '.' {
				s.nextch()
				s.tok = _DotDotDot
				break
			}
			s.rewind() // now s.ch holds 1st '.'

			switch tok {
			case token.IDENT, token.BREAK, token.CONTINUE, token.FALLTHROUGH, token.RETURN:
				insertSemi = true
			}
		} else {
			insertSemi = true
			tok = token.IDENT
		}
	case isDecimal(ch) || ch == '.' && isDecimal(rune(s.peek())):
		insertSemi = true
		tok, lit = s.scanNumber()
	default:
		s.next() // always make progress
		switch ch {
		case eof:
			if s.insertSemi {

	ch := s.next()
	for i := 1; s.isIdentRune(ch, i); i++ {
		ch = s.next()
	}
	return ch
}

func lower(ch rune) rune     { return ('a' - 'A') | ch } // returns lower-case ch iff ch is ASCII letter
func isDecimal(ch rune) bool { return '0' <= ch && ch <= '9' }
func isHex(ch rune) bool     { return '0' <= ch && ch <= '9' || 'a' <= lower(ch) && lower(ch) <= 'f' }

// digits accepts the sequence { digit | '_' } starting with ch0.