Hi, I am new to appian, how to duplicate this Java loop into Sail Expression?

a!localVariables(
    local!positionCollect: {1,2,3,4,5,6,7,8,9,10},
    local!polygonList: a!forEach(
        enumerate(length(local!positionCollect)/2)+1,
        type!Point(
            x: local!positionCollect[(fv!index*2)-1],
            y: local!positionCollect[(fv!index*2)]
        )
    ),
    local!polygonList
)

In Appian all functions and rules will return a value. In the code above, I have a list of positions defined as a list and then a polygonList which calls a!forEach() which will return a list. Also, the code above will only work if your positionCollect list is even.

a!localVariables(
    local!positionCollect: {1,2,3,4,5,6,7,8,9,10},
    local!polygonList: a!forEach(
        enumerate(length(local!positionCollect)/2)+1,
        type!Point(
            x: local!positionCollect[(fv!index*2)-1],
            y: local!positionCollect[(fv!index*2)]
        )
    ),
    local!polygonList
)

In Appian all functions and rules will return a value. In the code above, I have a list of positions defined as a list and then a polygonList which calls a!forEach() which will return a list. Also, the code above will only work if your positionCollect list is even.

You could structure the data differently and as the input provide a "list of lists" - that is a list of pairs of numbers, where each pair represents the x and y values:

a!localVariables(
  local!myListOfCoOrdinates: {
    { x: 1, y: 2},
    { x: 3, y: 4},
    { x: 5, y: 6},
    { x: 7, y: 8},
    { x: 9, y: 10}
  },
  a!forEach(
    items: local!myListOfCoOrdinates,
    expression: type!Point(
      x: fv!item.x,
      y: fv!item.y
    )
  )
)

or, indeed, you could leverage Appian's type casting capability:

a!localVariables(
  local!myListOfCoOrdinates: {
    { x: 1, y: 2},
    { x: 3, y: 4},
    { x: 5, y: 6},
    { x: 7, y: 8},
    { x: 9, y: 10}
  },
  cast(
    'type!{urn:com:appian:types:SJB}Point?list',
    local!myListOfCoOrdinates
  )
)

...so many cats, so many ways to skin them! 

I don't know how to thank you for your solution! I went through the document but there are no instruction about it! 

Thank you so much! It is works perfertly! Also, do you know what is the best way to learn Expression Rules instead of posting question here? Seems like the document skip over many concept..

Thank you for your answers!!