On Wed, May 21, 2014 at 8:12 AM, Ollie Frolovs <ollie.frolovs.2012@my.bristol.ac.uk> wrote:

Hello

I’ve been trying to use Random.self_init in Jane Street’s Core but every time I run my program it returns the same result as if the self_init is in fact completely deterministic. Two questions – what am I doing wrong and how do I make it “random” (as in returning different values on each run of the application).

I compile the following source into native code with “corebuild”.

When I run the program, the result is ALWAYS
1 0
1 1
0 1
0 2
0 3

I’ve also upload the code and the output from "opam list -i” on GitHub, if that’s more convenient https://gist.github.com/olliefr/d6312d8195e9a30aa80c

I believe I have the latest compiler/libraries. The system is OS X Mavericks.

Many thanks,

Ollie

--
(* SOURCE CODE BEGINS *)

open Core.Std

let _ = Random.self_init

(*
FIXME there must be something in the standard library to do this!

Iterate a function over a value, tail-recursively.
n: how many times
f: function to apply
a: initial value of the argument
*)
let rec iterate n f a =
if n<=0
then a
else iterate (n-1) f (f a)

(* Wandering Light *)
let light = (0,0)

let wander (x,y) =
match (1 + Random.int 4) with
1 -> (x+1, y)
| 2 -> (x, y+1)
| 3 -> (x-1, y)
| 4 -> (x, y+1)
| _ -> failwith "random direction is not 1 to 4, wtf?"

let render (x,y) = printf "%i %i\n" x y

let step light =
let newlight = wander light in
render newlight;
newlight

let _ = iterate 5 step (0,0)

(* THE END *)

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