I think the problem is that you aren't *calling* Random.self_init. To do so, change the line


  let _ = Random.self_init




to




  let () = Random.self_init ()




The value that _ is matching against in your program has type unit -> unit rather than just unit. 
—
Sent from Mailbox

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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