问没有变量赋值的linq中的绑定表达式

EN

static IO<Void> Foo()
{
    var foo = from i in Return(2)
              from _1 in Print("Enter a number")
              from input in ReadInt()
              from _2 in Print("You entered: " + input)
              from j in Increment(input).Bind(Square)
              from sum in Add(j, input)
              from _3 in Print("i = " + i)
              from _4 in Print("j = " + j)
              from condition in GreaterThan(j, 10)
              from _5 in If(condition,
                  Print("j is greater than 10"),
                  Print("j is not greater than 10"))
              from _6 in Print("sum = " + sum)
              select Void.Void;
    return foo;
}