[2020][ruby][18] refactor

2020/ruby/day_18.rb

@@ -35,18 +35,18 @@ def evaluate(input)
   ss = StringScanner.new(input)
   until ss.eos?
     ss.scan(/\s*/)
-    case
+    stack << case
              when n = ss.scan(/\d+/)
-      stack << stack.pop[n.to_i]
+               stack.pop[n.to_i]
              when ss.scan(/\+/)
-      stack << ->(x) { stack.pop + x }
+               ->(x) { stack.pop + x }
              when ss.scan(/\*/)
-      stack << ->(x) { stack.pop * x }
+               ->(x) { stack.pop * x }
              when ss.scan(/\(/)
-      stack << ->(x) { x }
+               ->(x) { x }
              when ss.scan(/\)/)
                n = stack.pop
-      stack << stack.pop[n]
+               stack.pop[n]
              else
                fail
              end