lexer/lexer.go
func New(input string) *Lexer {
	l := &Lexer{input: input, curLine: 1}
	l.readChar()
	return l
}
func New(input string) *Lexer {
	l := &Lexer{input: input, curLine: 1}
	l.readChar()
	return l
}
// New Lexer from the input string