Here is my code , could you please tell me where i'm going wrong... isn't plotting anything

Fern :=proc(n);

local pick,n;

n := NULL;

for n from 1 to n do

pick := rand();

if pick < 0.01 then

x[n+1] := 0;

y[n+1] := 0.16*y[n];

else if pick < 0.01 + 0.85 then

x[n+1] := 0.85*x[n] + 0.04*y[n] + 0;

y[n+1] := -0.04*x[n] + 0.85*y[n] + 1.6;

else if pick < 0.01 + 0.85 + 0.07 then

x[n+1] := 0.2*x[n] - 0.26*y[n] + 0;

y[n+1] := 0.23*x[n] + 0.22*y[n] + 1.6;

else

x[n+1] := -0.15*x[n] + 0.28*y[n] + 0;

y[n+1] := 0.26*x[n] + 0.24*y[n] + 0.44;

end if;

end do:

n := n , [x[n+1],y[n+1];

plot(n(12500), axes=NONE, style=point, symbol=POINT, scaling=constrained, colour=green);