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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Random number generation
Newsgroups: comp.lang.ada
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References: <864o9vbkwz.fsf@gareth.avalon.lan>
Date: Thu, 30 Dec 2010 14:04:05 +0100
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Date: 2010-12-30T14:04:03+01:00
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On Thu, 30 Dec 2010 11:43:40 +0100, Mart van de Wege wrote:

> Anyone care to at least point me to some documentation that explains
> what I'm doing wrong? 

Random generator is a stateful object, thus it cannot be local.

I suggest this is what you want:
--------------------------------------------------------------------------
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;

with Ada.Numerics.Discrete_Random;

procedure Rolltest is
   package Uniform is new Ada.Numerics.Discrete_Random (Natural);
   use Uniform;

   function Roll
            (  Dice     : Generator;
               Number   : in Positive;
		   Size     : in Positive;
		   Modifier : in Integer := 0
            )  return Integer is 
      Result : Integer := 0;
   begin
      for I in 1..Number loop
	   Result := Result + Random (Dice) mod Size;
      end loop;
      Result := Result + Modifier + Number;
      return Result;
   end Roll;

   Dice : Generator;
begin
   Reset (Dice);
   for I in 1..10 loop
      Put (Roll (Dice => Dice, Number => 3, Size => 6));
   end loop;
end Rolltest;
-------------------------------------------------------------------------
I added Number to the accumulated result because you did so in your example
by choosing the range 2..Size.

BTW, a sum of n realizations of a uniformly distributed random number is
distributed uniformly with the factor n. So you need not to run a cycle
within Roll:

   function Roll
            (  Dice     : Generator;
               Number   : in Positive;
		   Size     : in Positive;
		   Modifier : in Integer := 0
            )  return Integer is 
   begin
      return Number * ((Random (Dice) mod Size) + 1) + Modifier;
   end Roll;
 
-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de