NOTE: rhombus first try

Rhombus is Racket 2(maybe?), an another syntax style choose for Racket's User, one must write #lang rhombus to use it. To install, use

raco pkg install --auto rhombus-prototype

1. Expression and block form

1+1

begin:
  let v: 1
  v

val x :: Integer : 1
x+1

val mutable ha: 1
ha := 2
ha

def y: 1
y

def '$x @mul $y':
  '$x * $y'
2 @mul 3

def foo(x) :: Integer:
  x
foo(y)
fun bar(x :: Integer) :: Integer:
  x + 1

operator(x ! y):
  x + y
1 ! 2

class Book(name :: String, author :: String)
val b: Book("The Lord of the Rings", "J. R. R. Tolkien")
b.author