Documentation:OCLOperators let

Holds the result of an expression in a temporary reference to use later within the statement.

let statements can chained together.

Example 1

let x = 2 in
(   
    x + 4
)

Example 2

let l = Bag{1,2,3,4} in
(
    let m = l->collect(i|i*4) in
    (
        l->union(m)
    )
)