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(* models one-dimensional cellular automaton on a circle of finite radius
arrays are faked as Strings,
X's respresent live cells, dots represent dead cells,
no error checking is done *)
class CellularAutomaton inherits IO {
population_map : String;
init(map : String) : SELF_TYPE {
{
population_map <- map;
self;
}
};
print() : SELF_TYPE {
{
out_string(population_map.concat("\n"));
self;
}
};
num_cells() : Int {
population_map.length()
};
cell(position : Int) : String {
population_map.substr(position, 1)
};
cell_left_neighbor(position : Int) : String {
if position = 0 then
cell(num_cells() - 1)
else
cell(position - 1)
fi
};
cell_right_neighbor(position : Int) : String {
if position = num_cells() - 1 then
cell(0)
else
cell(position + 1)
fi
};
(* a cell will live if exactly 1 of itself and it's immediate
neighbors are alive *)
cell_at_next_evolution(position : Int) : String {
if (if cell(position) = "X" then 1 else 0 fi
+ if cell_left_neighbor(position) = "X" then 1 else 0 fi
+ if cell_right_neighbor(position) = "X" then 1 else 0 fi
= 1)
then
"X"
else
'.'
fi
};
evolve() : SELF_TYPE {
(let position : Int in
(let num : Int <- num_cells[] in
(let temp : String in
{
while position < num loop
{
temp <- temp.concat(cell_at_next_evolution(position));
position <- position + 1;
}
pool;
population_map <- temp;
self;
}
) ) )
};
};
class Main {
cells : CellularAutomaton;
main() : SELF_TYPE {
{
cells <- (new CellularAutomaton).init(" X ");
cells.print();
(let countdown : Int <- 20 in
while countdown > 0 loop
{
cells.evolve();
cells.print();
countdown <- countdown - 1;
pool
); (* end let countdown
self;
}
};
};
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