Question

Is there any built-in function that multiplies all elements of a list with another?

i.e

let xList = [1..30]

let yList = [1..30]

would give:

[(1,1),(1,2),(1,3)..ect]

Answer 1

This is called a cross-product or Cartesian product of lists. The easiest way to construct it is to use sequnce expressions – you can simply iterate over the two lists and yield all pairs:

let prod = [ for x in xList do
               for y in yList do
                 yield x,y ]

If you want to use higher-order functions, then you can use List.collect:

xList |> List.collect (fun x -> 
    yList |> List.map (fun y -> x, y))

For every value x from the xList, the lambda function generates a new list (such as [(x,1); (x,2); ... (x, n)]). The List.collect function then concatenates all these generated lists.