introduce the LabeListener to move instructions along when first code position changes

lib/risc/position/instruction_listener.rb

@@ -25,6 +25,7 @@ module Risc
     # Taking into account that BinaryCodes only take 13 instructions,
     # meaning that chain may have to be extended
     def position_changing(position , to)
+      Position.log.debug "Changing #{position} to #{to.to_s(16)}, bin #{Position.get(@binary)}"
       update_index(to)
       instruction = position.object
       return unless instruction.next
@@ -40,7 +41,7 @@ module Risc
 
     def update_index(to)
       index = (to - Position.get(@binary).at) / 4
-      raise "Invalid negative index #{@index} ,  #{Position.get(@binary)}" if index < Parfait::BinaryCode.type_length
+      raise "Invalid negative index #{index} ,  #{Position.get(@binary)}" if index < Parfait::BinaryCode.type_length
       while(index >= (Parfait::BinaryCode.memory_size - 1) )
         @binary = @binary.ensure_next
         index = (to - Position.get(@binary).at) / 4

lib/risc/position/label_listener.rb

@@ -0,0 +1,39 @@
+module Risc
+
+  # LabelListener is the one point that connects the BinaryCode
+  # and Instruction positions.
+  #
+  # LabelListener is instantiated with the first label of a Method
+  # and attached to the first BinaryCode.
+  #
+  # When the code moves, the label position is updated.
+  #
+  # The first code may get pushed by a previous method, and there is otherwise
+  # no way to react to this.
+  class LabelListener
+
+    attr_reader :label
+
+    # initialize with the first label of the method
+    def initialize(label)
+      @label = label
+    end
+
+
+    # The incoming position is the first BinaryCode of the method
+    # We simply position the Label (instance, see initialize) as the
+    # first entry in the BinaryCode, at BinaryCode.byte_offset
+    def position_changed(position)
+      label_pos = Position.get(@label)
+      label_pos.set(position + Parfait::BinaryCode.byte_offset)
+    end
+
+    # don't react to insertion, as the CodeListener will take care
+    def position_inserted(position)
+    end
+
+    # dont react, as we do the work in position_changed
+    def position_changing(position , to)
+    end
+  end
+end

lib/risc/position/position.rb

@@ -190,3 +190,4 @@ end
 require_relative "position_listener"
 require_relative "instruction_listener"
 require_relative "code_listener"
+require_relative "label_listener"