Question

I have two snippets of code that tries to convert a float list to a Vector3 or Vector2 list. The idea is to take 2/3 elements at a time from the list and combine them as a vector. The end result is a sequence of vectors.

    let rec vec3Seq floatList =
        seq {
            match floatList with
            | x::y::z::tail -> yield Vector3(x,y,z)
                               yield! vec3Seq tail
            | [] -> ()
            | _ -> failwith "float array not multiple of 3?"
            }

    let rec vec2Seq floatList =
        seq {
            match floatList with
            | x::y::tail -> yield Vector2(x,y)
                            yield! vec2Seq tail
            | [] -> ()
            | _ -> failwith "float array not multiple of 2?"
            }

The code looks very similiar and yet there seems to be no way to extract a common portion. Any ideas?

Answer 1

Here’s one approach. I’m not sure how much simpler this really is, but it does abstract some of the repeated logic out.

let rec mkSeq (|P|_|) x =
  seq {
    match x with
    | P(p,tail) -> 
        yield p
        yield! mkSeq (|P|_|) tail
    | [] -> ()
    | _ -> failwith "List length mismatch" }

let vec3Seq =
  mkSeq (function
  | x::y::z::tail -> Some(Vector3(x,y,z), tail)
  | _ -> None)