const target = "METHINKS IT IS LIKE A WEASEL";
const C = 100;  // Number of children in each generation.
const P = 0.05; // Mutation probability.
const A2ZS = ["A".."Z"].walk().append(" ").concat();
fcn fitness(s){ Utils.zipWith('!=,target,s).sum(0) } // bigger is worser
fcn rnd{ A2ZS[(0).random(27)] }
fcn mutate(s){ s.apply(fcn(c){ if((0.0).random(1) < P) rnd() else c }) }

parent := target.len().pump(String,rnd);  // random string of "A..Z "
gen:=0; do{  // mutate C copies of parent and pick the fittest
   parent = (0).pump(C,List,T(Void,parent),mutate)
	    .reduce(fcn(a,b){ if(fitness(a)<fitness(b)) a else b });
   println("Gen %2d, dist=%2d: %s".fmt(gen+=1, fitness(parent), parent));
}while(parent != target);