Re: [Caml-list] Random.self_init in Jane Street Core

["Nathan Mishra Linger" <nathan.mishralinger@gmail.com>]

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Oops. Nevermind. —
Sent from Mailbox

On Thu, May 22, 2014 at 8:12 PM, Nathan Mishra Linger
<nathan.mishralinger@gmail.com> wrote:

> 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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