bit of code docs

lib/mom/instruction/label.rb

@@ -0,0 +1,33 @@
+module Mom
+
+  # A Label is the only legal target for a branch (this is true in Mom and Risc)
+  #
+  # In the dynamic view (runtime) where the instructions form a graph,
+  # branches fan out, Labels collect. In other words a branch is the place where
+  # several roads lead off, and a Label where several roads arrive.
+  #
+  # A Label has a name which is mainly used for debugging.
+  #
+  class Label < Instruction
+    attr_reader :name
+    def initialize(name)
+      @name = name
+    end
+
+    # A Mom::Label converts one2one to a Risc::Label. So in a way it could not be more
+    # simple.
+    # Alas, since almost by definition several roads lead to this label, all those
+    # several converted instructions must also point to the identical label on the
+    # risc level.
+    #
+    # This is achieved by caching the created Risc::Label in an instance variable.
+    # All branches that lead to this label can thus safely call the to_risc and
+    # whoever calls first triggers the labels creation, but all get the same label.
+    #
+    # Off course some specific place still has to be responsible for actually
+    # adding the label to the instruction list (usually an if/while)
+    def to_risc(compiler)
+      @risc_label ||= Risc::Label.new(self,name)
+    end
+  end
+end