MIHS JT and CA p.3

globals [grass]  ;; keep track of how much grass there is
;; Sheep and wolves are both breeds of turtle.
breed [sheep a-sheep]  ;; sheep is its own plural, so we use "a-sheep" as the singular.
breed [frogs frog]
breed [wolves wolf]
turtles-own [energy]       ;; both wolves and sheep have energy
patches-own [countdown]

to setup
  clear-all
  ask patches [ set pcolor green ]
  ;; check GRASS? switch.
  ;; if it is true, then grass grows and the sheep eat it
  ;; if it false, then the sheep don't need to eat
  if grass? [
    ask patches [
      set pcolor one-of [green brown]
      if-else pcolor = green
        [ set countdown grass-regrowth-time ]
        [ set countdown random grass-regrowth-time ] ;; initialize grass grow clocks randomly for brown patches
    ]
  ]
  set-default-shape frogs "frog"
  create-frogs initial-number-frogs [ set color blue
    set size 1
    set energy random (2 * frog-gain-from-food)
    setxy random-xcor random-ycor
  ]
  set-default-shape sheep "sheep"
  create-sheep initial-number-sheep  ;; create the sheep, then initialize their variables
  [
    set color white
    set size 1.5  ;; easier to see
    set label-color blue - 2
    set energy random (2 * sheep-gain-from-food)
    setxy random-xcor random-ycor
  ]
  set-default-shape wolves "wolf"
  create-wolves initial-number-wolves  ;; create the wolves, then initialize their variables
  [
    set color black
    set size 2  ;; easier to see
    set energy random (2 * wolf-gain-from-food)
    setxy random-xcor random-ycor
  ]
  display-labels
  set grass count patches with [pcolor = green]
  reset-ticks
end 

to go
  if not any? turtles [ stop ]
  ask sheep [
    move
    if grass? [
      set energy energy - 1  ;; deduct energy for sheep only if grass? switch is on
      catch-frogs
      eat-grass
    ]
    death
    reproduce-sheep
  ]
  ask wolves [
    move
    set energy energy - 1  ;; wolves lose energy as they move
    catch-sheep
    death
    reproduce-wolves
  ]
  ask frogs [
  move
  set energy energy - 1
  catch-wolves
  death
  reproduce-frogs
  ]
  if grass? [ ask patches [ grow-grass ] ]
  set grass count patches with [pcolor = green]
  tick
  display-labels
end 

to move  ;; turtle procedure
  rt random 50
  lt random 50
  fd 1
end 

to eat-grass  ;; sheep procedure
  ;; sheep eat grass, turn the patch brown
  if pcolor = green [
    set pcolor brown
    set energy energy + sheep-gain-from-food  ;; sheep gain energy by eating
  ]
end 

to reproduce-sheep  ;; sheep procedure
  if random-float 100 < sheep-reproduce [  ;; throw "dice" to see if you will reproduce
    set energy (energy / 2)                ;; divide energy between parent and offspring
    hatch 1 [ rt random-float 360 fd 1 ]   ;; hatch an offspring and move it forward 1 step
  ]
end 

to reproduce-wolves  ;; wolf procedure
  if random-float 100 < wolf-reproduce [  ;; throw "dice" to see if you will reproduce
    set energy (energy / 2)               ;; divide energy between parent and offspring
    hatch 1 [ rt random-float 360 fd 1 ]  ;; hatch an offspring and move it forward 1 step
  ]
end 

to reproduce-frogs
  if random-float 100 < frog-reproduce [
    set energy (energy / 2)
    hatch 1 [ rt random-float 360 fd 1 ]
  ]
end 

to catch-sheep  ;; wolf procedure
  let prey one-of sheep-here                    ;; grab a random sheep
  if prey != nobody                             ;; did we get one?  if so,
    [ ask prey [ die ]                          ;; kill it
      set energy energy + wolf-gain-from-food ] ;; get energy from eating
end 

to catch-wolves
  let prey one-of wolves-here
  if prey != nobody
  [ ask prey [ die ]
    set energy energy + frog-gain-from-food ]
end 

to catch-frogs
  let prey one-of frogs-here
  if prey != nobody
  [ ask prey [ die ]
    set energy energy + sheep-gain-from-food ]
end 

to death  ;; turtle procedure
  ;; when energy dips below zero, die
  if energy < 0 [ die ]
end 

to grow-grass  ;; patch procedure
  ;; countdown on brown patches: if reach 0, grow some grass
  if pcolor = brown [
    ifelse countdown <= 0
      [ set pcolor green
        set countdown grass-regrowth-time ]
      [ set countdown countdown - 1 ]
  ]
end 

to display-labels
  ask turtles [ set label "" ]
  if show-energy? [
    ask wolves [ set label round energy ]
    if grass? [ ask sheep [ set label round energy ] ]
  ]
end 


; Copyright 1997 Uri Wilensky.
; See Info tab for full copyright and license.