repeat until no more exception

move class to where it is used

lib/risc/assembler.rb

@@ -1,6 +1,4 @@
 module Risc
-  class LinkException < Exception
-  end
   # Assemble the object machine into a binary.
   # Assemble first to get positions, then write
 

lib/risc/binary_writer.rb

@@ -12,14 +12,25 @@ module Risc
     end
 
     # write into the given BinaryCode instance
+    # LinkException may be thrown, possibly several times
+    # So repeat until it works
     def assemble( instruction )
+      ok = false
+      until(ok)
+        begin
+          assemble_all(instruction)
+          ok = true
+        rescue LinkException
+        end
+      end
+    end
+
+    # Go through and assemble all instructions.
+    # Assembly may cause LinkException, which is caught by caller
+    def assemble_all( instruction )
       @index = 1
       while(instruction)
-        begin
+        instruction.assemble(self)
-          instruction.assemble(self)
-        rescue LinkException
-          instruction.assemble(self)
-        end
         instruction = instruction.next
       end
     end
@@ -30,4 +41,19 @@ module Risc
     end
   end
 
+  # A LinkException is raised when the arm code can't fit a constant into _one_
+  # instruction. This is kind of unavoidable with arm.
+  #
+  # Off course the problem could be fixed without the exception, but the exception
+  # means all subsequent Instructions, including labels/jump targets move.
+  # Thus changing jump instructions to those labels.
+  # So the whole method has to be reassembled and (at least) the instructions beyond
+  # repositioned. Ie a non-local problem, and so the Exception.
+  #
+  # Note: In the future i hope to have a more flexible system, possibly with position
+  # listeners and change events. Because positions chaning is normal, not exceptional.
+  #
+  class LinkException < Exception
+  end
+
 end