Dawkins Weasel Remix

globals
[
  uppercase
  lowercase
  parent-string
  generation
  all-done
]

to setup
  clear-all
  set uppercase "ABCDEFGHIJKLMNOPQRSTUVWXYZ "
  set lowercase "abcdefghijklmnopqrstuvwxyz"
  setup-intial-string
  initialize-string
  set generation 0
  set all-done false
  reset-ticks
end 

to go

  if all-done [ stop ] ; this line prevents the simulation from continuing to print out the following at every timestep after completion:

  if (with-selection and go-with-selection = 0 ) or (not with-selection and go-without-selection = 0) [ ; simulation found an exact matching phrase
    set all-done true
    print word "It took " word generation word " generations of " word number-of-offspring " offspring to evolve to the target phrase."
    stop ]

  tick
end 

to output-generation
  output-print (word generation "   " parent-string)
end 

to-report go-with-selection ; go function used when WITH-SELECTION is TRUE

  let offspring-string parent-string
  let top-offspring-string parent-string
  let top-offspring-score get-score parent-string
  let uppercase-length length uppercase
  let string-length length parent-string

  set generation generation + 1

  let i 0

  ; EACH OFFSPRING LOOP
  while [i < number-of-offspring]
  [
    set offspring-string parent-string;
    let j 0

    ; EACH CHARACTER LOOP
    while [j < string-length]
    [
      let mutation-probability random-float 1.0
      if mutation-probability < mutation-rate [
        let random-letter item (random uppercase-length) uppercase
        set offspring-string replace-item j offspring-string random-letter
      ]
      set j j + 1
    ]

    ; compares current offspring with top offspring
    let current-offspring-score get-score offspring-string
    if current-offspring-score < top-offspring-score [
      set top-offspring-string offspring-string
      set top-offspring-score current-offspring-score
    ]

    set i i + 1
  ]
  set parent-string top-offspring-string
  output-generation
  report top-offspring-score
end 

to-report go-without-selection ; go function used when WITH-SELECTION is FALSE
  let uppercase-length length uppercase
  set generation generation + 1

  let i 0
  while [i < length parent-string]
    [
      let mutation-probability random-float 1.0
      if mutation-probability < mutation-rate [
        let random-letter item (random uppercase-length) uppercase
        set parent-string replace-item i parent-string random-letter
      ]
      set i i + 1
    ]
  output-generation
  report get-score parent-string
end 

to setup-intial-string
  let string-length length target-phrase
  if string-length < 1 [ set target-phrase "SORRY DAVE I CANNOT ALLOW THAT" ]
  let i 0
  while [i < string-length] ; replace lowercase with uppercase:
  [
    if (not member? item i target-phrase uppercase) [
      ifelse (member? item i target-phrase lowercase)
      [ set target-phrase replace-item i target-phrase item (position (item i target-phrase) lowercase) uppercase ]
      [ set target-phrase replace-item i target-phrase " " ]
    ]
    set i i + 1
  ]
end 

to initialize-string
  let initial-string target-phrase
  let string-length length initial-string
  let uppercase-length length uppercase
  let index 0
  while [index < string-length]
  [
    let random-letter item (random uppercase-length) uppercase
    set initial-string replace-item index initial-string random-letter
    set index index + 1
  ]
  set parent-string initial-string;
  set parent-string initial-string
  output-generation
end 

to-report get-score [input-string] ; score used to determine how well the INPUT-STRING matches the TARGET-PHRASE

  let string-length length input-string
  let score string-length
  let index 0
  while [index < string-length]
  [
    let goal-letter item index target-phrase
    let input-letter item index input-string
    if goal-letter = input-letter [set score score - 1]
    set index index + 1
  ]

  report score
end