diff --git a/src/objects.cr b/src/objects.cr
index aec05b2..4e22b60 100644
--- a/src/objects.cr
+++ b/src/objects.cr
@@ -53,23 +53,11 @@ module Objects
     abstract def inspect : String
 
     def if_not_error(& : MObject -> MObject?) : MObject?
-      case self
-      when MError
-        return self
-      else
-        return yield self
-      end
+      yield self
     end
 
     def is_truthy? : Bool
-      case self
-      when MBoolean
-        return self.value
-      when MNull
-        return false
-      else
-        return true
-      end
+      true
     end
   end
 
@@ -149,6 +137,10 @@ module Objects
     def initialize(@message : String)
     end
 
+    def if_not_error(& : MObject -> MObject?) : MObject?
+      self
+    end
+
     def inspect : String
       return "ERROR: #{@message}"
     end
@@ -162,20 +154,23 @@ module Objects
     def inspect : String
       return "null"
     end
+
+    def is_truthy? : Bool
+      false
+    end
   end
 
   class MBoolean < MValue(Bool)
     def hash_type : HashType
-      return HashType::Boolean
+      HashType::Boolean
+    end
+
+    def same?(other : self)
+      other.value == @value
     end
 
     def same?(other)
-      case other
-      when MBoolean
-        return other.value == @value
-      else
-        return false
-      end
+      false
     end
 
     # def object_id
@@ -185,6 +180,10 @@ module Objects
     def hash_key : HashKey
       return HashKey.new(hash_type, (@value ? 1 : 0).to_u64)
     end
+
+    def is_truthy? : Bool
+      value
+    end
   end
 
   class MString < MValue(String)
diff --git a/src/vm.cr b/src/vm.cr
index 3a0c6bf..58099a4 100644
--- a/src/vm.cr
+++ b/src/vm.cr
@@ -4,7 +4,7 @@ require "./objects"
 
 macro execute_build_and_push(col)
   num_elements = Code.read_int(ins, ip + 1)
-  current_frame.ip += 2
+  current_frame.ip &+= 2
   {{col}} = build_{{col}}(@sp - num_elements, @sp)
   @sp -= num_elements
   push({{col}})
@@ -41,6 +41,9 @@ module Vm
     @frames = Array(Vm::Frame?).new(MAX_FRAME_SIZE) { nil }
     @frame_index = 1
     @globals = [] of MObject
+    private getter current_frame : Frame do
+      @frames[@frame_index - 1].not_nil!
+    end
 
     def initialize(@bytecode : Bytecode)
       @constants = @bytecode.constants
@@ -60,14 +63,14 @@ module Vm
       ins : Instructions
       op : Opcode
       while current_frame.ip < current_frame.instructions.size - 1
-        current_frame.ip += 1
+        current_frame.ip &+= 1
         ip = current_frame.ip
         ins = current_frame.instructions
         op = Opcode.new(ins[ip].to_i)
         case op
         when Opcode::OpConstant
           const_index = Code.read_int(ins, ip + 1)
-          current_frame.ip += 2
+          current_frame.ip &+= 2
           push(@constants[const_index])
         when Opcode::OpPop
           pop
@@ -85,7 +88,7 @@ module Vm
           execute_bang_operator
         when Opcode::OpJumpNotTruthy
           pos = Code.read_int(ins, ip + 1)
-          current_frame.ip += 2
+          current_frame.ip &+= 2
           condition = pop
           if !condition.is_truthy?
             current_frame.ip = pos - 1
@@ -97,7 +100,7 @@ module Vm
           current_frame.ip = pos - 1
         when Opcode::OpSetGlobal
           global_index = Code.read_int(ins, ip + 1)
-          current_frame.ip += 2
+          current_frame.ip &+= 2
           if global_index == @globals.size
             @globals << pop.not_nil!
           else
@@ -105,7 +108,7 @@ module Vm
           end
         when Opcode::OpGetGlobal
           global_index = Code.read_int(ins, ip + 1)
-          current_frame.ip += 2
+          current_frame.ip &+= 2
           push(@globals[global_index])
         when Opcode::OpArray
           execute_build_and_push array
@@ -118,11 +121,11 @@ module Vm
         when Opcode::OpClosure
           const_index = Code.read_int(ins, ip + 1)
           num_free = Code.read_byte(ins, ip + 3)
-          current_frame.ip += 3
+          current_frame.ip &+= 3
           push_closure(const_index, num_free.to_i)
         when Opcode::OpCall
           num_args = Code.read_byte(ins, ip + 1)
-          current_frame.ip += 1
+          current_frame.ip &+= 1
           execute_call(num_args.to_i)
         when Opcode::OpReturnValue
           return_value = pop
@@ -135,21 +138,21 @@ module Vm
           push(VM_NULL)
         when Opcode::OpSetLocal
           local_index = Code.read_byte(ins, ip + 1)
-          current_frame.ip += 1
+          current_frame.ip &+= 1
           frame = current_frame
           @stack[frame.base_pointer + local_index.to_i] = pop
         when Opcode::OpGetLocal
           local_index = Code.read_byte(ins, ip + 1)
-          current_frame.ip += 1
+          current_frame.ip &+= 1
           frame = current_frame
           push(@stack[frame.base_pointer + local_index.to_i].not_nil!)
         when Opcode::OpGetBuiltin
           built_index = Code.read_byte(ins, ip + 1)
-          current_frame.ip += 1
+          current_frame.ip &+= 1
           push(Objects::BUILTINS[built_index.to_i][1])
         when Opcode::OpGetFree
           free_index = Code.read_byte(ins, ip + 1)
-          current_frame.ip += 1
+          current_frame.ip &+= 1
           current_closure = current_frame.cl
           push(current_closure.free[free_index.to_i])
         when Opcode::OpCurrentClosure
@@ -164,16 +167,12 @@ module Vm
       return @stack[@sp]?
     end
 
-    private def current_frame : Vm::Frame
-      return @frames[@frame_index - 1].not_nil!
-    end
-
     private def push(obj : MObject)
       if @sp > STACK_SIZE
         raise VMException.new("stack overflow")
       end
       @stack[@sp] = obj
-      @sp += 1
+      @sp &+= 1
     end
 
     private def pop : MObject?
@@ -282,7 +281,7 @@ module Vm
       i = start_index
       while i < end_index
         elements[i - start_index] = @stack[i]
-        i += 1
+        i &+= 1
       end
       return MArray.new(elements)
     end
@@ -385,12 +384,14 @@ module Vm
 
     private def push_frame(frame : Frame)
       @frames[@frame_index] = frame
-      @frame_index += 1
+      @current_frame = nil
+      @frame_index &+= 1
     end
 
     private def pop_frame : Frame
       @frame_index -= 1
-      return @frames[@frame_index].not_nil!
+      @current_frame = nil
+      @frames[@frame_index].not_nil!
     end
   end