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Task/Evolutionary-algorithm/OoRexx/evolutionary-algorithm.rexx

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+/* Weasel.rex - Me thinks thou art a weasel. - G,M.D. - 2/25/2011 */
+arg C M
+/* C is the number of children parent produces each generation. */
+/* M is the mutation rate of each gene (character) */
+
+call initialize
+generation = 0
+do until parent = target
+   most_fitness = fitness(parent)
+   most_fit     = parent
+   do C
+      child = mutate(parent, M)
+      child_fitness = fitness(child)
+      if child_fitness > most_fitness then
+      do
+         most_fitness = child_fitness
+         most_fit = child
+         say "Generation" generation": most fit='"most_fit"', fitness="left(most_fitness,4)
+      end
+   end
+   parent = most_fit
+   generation = generation + 1
+end
+exit
+
+initialize:
+   target   = "METHINKS IT IS LIKE A WEASEL"
+   alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ "
+   c_length_target = length(target)
+   parent  = mutate(copies(" ", c_length_target), 1.0)
+   do i = 1 to c_length_target
+      target_ch.i = substr(target,i,1)
+   end
+return
+
+fitness: procedure expose target_ch. c_length_target
+   arg parm_string
+   fitness = 0
+   do i_target = 1 to c_length_target
+      if substr(parm_string,i_target,1) = target_ch.i_target then
+         fitness = fitness + 1
+   end
+return fitness
+
+mutate:procedure expose alphabet
+arg string, parm_mutation_rate
+   result = ""
+   do istr = 1 to length(string)
+      if random(1,1000)/1000 <= parm_mutation_rate then
+         result = result || substr(alphabet,random(1,length(alphabet)),1)
+      else
+         result = result || substr(string,istr,1)
+   end
+return result