ruby - Raise Undefined local variable or method -

ok understand local variable , global variable, got exercise 40 on learnrubythehardway credit ask each method on hash.

$cities = {"ca" => "san francisco",           "mi" => "detroit",           "fl" => "jacksonville"}  #adding new kay new value $cities["ny"] = "new york" $cities["or"] = "portland"   def loop(map,state)     $cities.each |map,state|          if map.include? state             return map[state]           else             return "not found."          end    end end  $cities[:find] = method(:loop)      while true         print "state? (enter quit) "        state = gets.chomp         break if state.empty?         #this line important ever! study!        puts $cities[:find].call(cities,state)     end 

the error giving me undefined local variable or method 'cities'

anyway understand local variable can access in main file, when comes global variable, can assign $ , access method inside itself.

i have research on other undefined variable or method, theirs pretty straight forward.

this line problem:

puts $cities[:find].call(cities,state) 

there no local variable cities in scope, hence error.

to honest find whole example extremely contrived , pretty horrible. times needed global variables in last 10+ years of writing ruby can counted on fingers of 1 hand spare.

since seem confused global , local variables, have @ this:

$foo = "foo" defined?($foo) #=> "global-variable" defined?(foo) #=> nil 

this what's happening in example $cities , cities (note missing $).