Re: Request for critics

["Steve" <nospam_steved94@comcast.net>]

I've been writing a lot of time critical code lately so my approach to 
coding may be a little out of the norm, but here is some code with the same 
functionality.  Columns should align nicely if you view them in a fixed 
pitch font.:

with Ada.Text_IO;
use Ada.Text_IO;

procedure Automata is

    Size      : constant := 66;
    Max_Steps : constant := 31;

    type Cell_State is (Active, Inactive);
    type Row_Of_Cells is array (1 .. Size) of Cell_State;

    type State_To_Char is array( Cell_State'Range ) of Character;
    State_Char : constant State_To_Char := ( Active => '*', Inactive => ' 
' );

    procedure Show(Row : in Row_Of_Cells) is
    begin
       for I in Row_Of_Cells'Range loop
          Put( State_Char( Row(I) ) );
       end loop;
       New_Line;
    end Show;

    type State_Map is array( Cell_State'Range, Cell_State'Range, 
Cell_State'Range ) of Cell_State;

    New_State : constant State_Map :=
       ( Active =>   ( Active =>   ( Active   => Inactive,     -- Active 
Active   Active   => Inactive
                                     Inactive => Active ),     -- Active 
Active   Inactive => Active
                       Inactive => ( Active   => Inactive,     -- Active 
Inactive Active   => Inactive
                                     Inactive => Active ) ),   -- Active 
Inactive Inactive => Active
         Inactive => ( Active =>   ( Active   => Active,       -- Inactive 
Active   Active   => Active
                                     Inactive => Inactive ),   -- Inactive 
Active   Inactive => Inactive
                       Inactive => ( Active   => Active,       -- Inactive 
Inactive Active   => Active
                                     Inactive => Inactive ) )  -- Inactive 
Inactive Inactive => Inactive
       );

begin
    declare
       Automata : Row_Of_Cells := (Size / 2 => Active, others => Inactive);
    begin
       Show(Automata);
       for Step in 1 .. Max_Steps loop
          declare
             New_Automata : Row_Of_Cells := (others => Inactive);
          begin
             for Cell_Index in
               Row_Of_Cells'First + 1 .. Row_Of_Cells'Last - 1 loop

                New_Automata(Cell_Index) := New_State(
                   Automata(Cell_Index - 1),
                   Automata(Cell_Index),
                   Automata(Cell_Index + 1));

             end loop;
             Automata := New_Automata;
          end;
          Show(Automata);
       end loop;
    end;
end Automata;


"Maciej Sobczak" <no.spam@no.spam.com> wrote in message 
news:dvr7a5$9o3$1@sunnews.cern.ch...
> For the purpose of my learning, please criticise the following code:
[snip]

> <problem-description>
> The above is a short simulation of one particular 1D cellular automata 
> (the state of the whole automata is printed as a single line and the time 
> progresses downwards on the printout), where the next state of each cell 
> is a function of the current states in the immediate neighbourhood of the 
> given cell. In other words, given ABCDEFGH as a state of the automata, the 
> next state of cell D is a function of cells C, D and E. Taking two 
> possible states, there are 256 possible rules. The above program simulates 
> only one of them.
> </problem-description>
>
> The goal is the readability and proper expression of the problem.
>
> How do you name loop control variables for array traversals? Is 
> "Cell_Index" overly verbose and would be "I" just enough?
>
In this example of code, IMHO "I" would be enough.
There is only one index involved and the loop is small.  Personally I tend 
to use a more expressive index name for all cases, and would probably use 
Cell_Index, Data_Index, Index, or something similar.

> Would you drop the Cell_Triplet type and pass the neighbourhood as three 
> separate parameters instead?
>

In this case I would rop Cell_Triplet since it doesn't add anything to the 
readability and introduces a new data type and required conversions.  In my 
experience, for the simple cases less is better.

> And so on. Pleasy be picky with every aspect you find important.
>
> Any performance considerations for this code (except, of course, that 
> Put() is called for each cell and might be replaced by whole-line 
> printouts instaed)?

The performance change you'll note in my modified implementation is the use 
of a lookup table for New_State instead of a function.  I think it is easier 
to interpret the mapping that takes place in the lookup table than analyzing 
the code.

You'll also note that I moved the definition of Automata into a declare 
block in the main procedure.  I strive to restrict the scope of variables as 
much as possible.

Normally I also avoid using variable names that are the same as package 
names.  It may be legal, but it may also be confusing.

In your original code the state mapping really only depended on the two 
neighbors, so the State_Map really only needs to be 2x2 rather than the 3x3 
in my example.  I chose to implement 3x3 since it would make it easier to 
define other mappings.

>
> BTW: The C version is just a bit shorter:
>
> #include <stdio.h>
> int main(){char s[]=
> "                                *                                 "
> ;char p,n;int st,i;puts(s);for(st=0;st!=31;++st){p=' 
> ';for(i=1;i!=65;++i){n=(s[i-1]^s[i+1])|0x20;s[i-1]=p;p=n;}s[i-1]=p;puts(s);}return 
> 0;}
>
> ;-)  (the last three characters are not part of the program)
>

You can generate line noise in Ada too.  But it is a bit harder to do, and 
after all that is not the objective.

I hope this helps,

Steve
(The Duck)

> -- 
> Maciej Sobczak : http://www.msobczak.com/
> Programming    : http://www.msobczak.com/prog/