CHARSET=: 'ABCDEFGHIJKLMNOPQRSTUVWXYZ '
NPROG=:   100                            NB. number of progeny (C)
MRATE=:   0.05                           NB. mutation rate

create  =: (?@$&$ { ])&CHARSET           NB. creates random list from charset of same shape as y
fitness =: +/@:~:"1
copy    =: # ,:
mutate  =: &(>: $ ?@$ 0:)(`(,: create))} NB. adverb
select  =: ] {~ (i. <./)@:fitness        NB. select fittest member of population

nextgen =: select ] , [: MRATE mutate NPROG copy ]
while   =: conjunction def '(] , (u {:))^:(v {:)^:_ ,:'

evolve=: nextgen while (0 < fitness) create