Supply & Demand

Globals [price]
Breed [Buyers Buyer]
Breed [Cars Car]
Buyers-own [willingtopay]
Cars-own [willingtosellfor]
turtles-own [partner]

to setup
  
  clear-all                                                     ;clear the world
  create-Buyers 50                                              ;create buyers, put them in random places
  [
  setxy random-xcor random-ycor
  ]
  create-Cars 50                                                ;create cars, put them in random places
  [
   setxy random-xcor random-ycor
  ]
  ask buyers [set shape "buyersleeping"]                        ;give buyers default neutral shapes
  ask cars [set shape "carsleeping"]                            ;give cars default neutral shapes        
  ask Buyers [set willingtopay (who + 50 + Change-in-Demand)]    ;set price buyers are willing to pay
  ask Cars [set willingtosellfor (who + 1 - Change-in-Supply)] ;set price cars are willing to sell for
  set price Initial-Price                                       ;converts price set by slider into variable that can change
end 

to go
  ;these commands repeat most of the startup procedures for when "go" is called after a price change
  ask buyers [set shape "buyersleeping"]
  ask cars [set shape "carsleeping"]
  ;ask Buyers [set willingtopay (who + 1 + Change-in-Demand)]
  ;ask Cars [set willingtosellfor (who - 49 - Change-in-Supply)]
  ask turtles [set partner nobody] 
  ask turtles [setxy random-xcor random-ycor]
  
  ;if you're a buyer willing to buy and haven't bought, show that you're looking
  ask buyers [if willingtopay >= price and partner = nobody and not any? buyers with [shape = "buyermad"][set shape "buyerlooking"]]
  
  ;if you're a car willing to sell haven't sold, and there are buyers, show that you're selling.
  ask cars [if willingtosellfor <= price and partner = nobody and not any? cars with [shape = "carmad"][set shape "carlooking"]]
  
  ;if you're a buyer willing to buy and haven't bought, find a car to buy
  ask buyers [if shape = "buyerlooking" [findseller]]
  
  ;if you're a car who wants to sell and there are no buyers left, look angry
  ask cars [if willingtosellfor <= price and partner = nobody and not any? buyers with [shape = "buyerlooking"] [set shape "carmad"]]
  
  ;if nobody is looking to buy or sell, stop and announce the equilibrium price ahs been reached
  if not any? cars with [shape = "carlooking"] 
     and not any? cars with [shape = "carmad"]
        and not any? buyers with [shape = "buyerlooking"] 
           and not any? buyers with [shape = "buyermad"]
              [output-print " " output-type "Equilibrium price reached! " output-type count cars with [partner != nobody] output-type " Cars sold for $" output-type price output-type " each."  stop]
  
  ;if buyers and cars are angry, and they are willing to adjust prices, make them adjust their prices
  if any? buyers with [shape = "buyermad"] and price-adjusting [raiseprice]
  if any? cars with [shape = "carmad"] and price-adjusting [lowerprice]
  
  ;if buyers and cars are angry, but they are not willing to adjust prices, stop and announced they are angry
  if any? buyers with [shape = "buyermad"] and not price-adjusting [output-print "Buyers are angry!" stop]
  if any? cars with [shape = "carmad"] and not price-adjusting [output-print "Sellers are angry!" stop]
end 

to findseller
  ;if there are cars who want to buy, but can't, make them mad
  ask buyers [if willingtopay >= price and partner = nobody and not any? cars with [shape = "carlooking"] [set shape "buyermad"]]
  
  ;if there are sellers who want to sell, but can't, make them mad
  ask cars [if willingtosellfor <= price and partner = nobody and not any? buyers with [shape = "buyerlooking"] [set shape "carmad"]]
  
  ;if there are cars left who want to be sold, wander around and look for them
  if any? cars with [shape = "carlooking"] and partner = nobody [lt random 40 rt random 40 fd 1 checkseller]
end 

to checkseller
  ;if there is an unsold car who wants to sell on this spot, buy it and make both of you happy.
  if any? other turtles-here with [(partner = nobody) and (shape = "carlooking")]
       [set partner one-of other turtles-here with [partner = nobody and shape = "carlooking"] 
       set shape "buyerhappy"
       ask partner [set partner myself set shape "carhappy"]]
  update-plot
  
  ;if there's not car here, look somewhere else
  if not any? other turtles-here with [shape = "carlooking"][findseller]
end 

to raiseprice
  ;annoucne your are raising the price, then raise the price
  Output-print "Angry Buyers with no cars offer to pay more." output-type "Price rises to $" output-type price + 1 output-print "." 
         output-print " "
  set price (price + 1)
  ;wait 2
  go
end 

to lowerprice
  ;announce you are lowering the price, then lower the price
  Output-print "Sellers angry nobody will buy their car offer lower prices." output-type "Price drops to $" output-type price - 1
       output-print "." output-print " "
  set price (price - 1)
 ; wait 2
  go
end 

to update-plot
set-current-plot "Change in Price"
set-current-plot-pen "Price"
plot price
set-current-plot "Change in Quantity"
set-current-plot-pen "cars sold"
plot count cars with [partner != nobody]
end