(* finished and correct, for ever *)
fun evens([]) = []
|   evens([value]) = [value]
|   evens(first::second::rest) = first :: evens(rest);

val test = [3, 0, 1, ~5, 8];

(* Computes n!, or 1 * 2 * 3 * ... * n-1 * n.
   Precondition: n >= 0. *)
fun factorial(0) = 1
|   factorial(n) = n * factorial(n - 1);

fun fibonacci(1) = 1
|   fibonacci(2) = 1
|   fibonacci(n) = fibonacci(n - 1) + fibonacci(n - 2);

(* an inexhaustive pattern *)
fun silly(0) = 1;


(* The distance between points (x1,y1),(x2,y2). *)
fun dist(x1, y1, x2, y2) =
    let
        val dx = x2 - x1
        val dy = y2 - y1
        val dy2 = dy * dy
    in
        Math.sqrt(dx * dx + dy2)
    end;