implement [] for RiscValue for the dsl

lib/mom/instruction/message_setup.rb

@@ -60,8 +60,11 @@ module Mom
     def get_message_to( compiler , message)
       Risc.build(compiler) do
         space << Parfait.object_space
+        #message << space[:first_message]
+        #risc << Risc.slot_to_reg(source + "get next message" , space , :first_message , message)
       end
-
+    end
+    def nnop
       space = compiler.use_reg(:Space)
       risc = Risc.load_constant("message setup move method" , Parfait.object_space ,space)
       risc << Risc.slot_to_reg(source + "get next message" , space , :first_message , message)

lib/risc/builder.rb

@@ -22,17 +22,14 @@ module Risc
       return built
     end
     def add_instruction(ins)
-      if(built)
+      if(@built)
-        built << ins
+        @built << ins
       else
         @built = ins
       end
     end
   end
 
-  class RValue
-  end
-
   def self.build(compiler, &block)
     Builder.new(compiler).build( &block )
   end

lib/risc/risc_value.rb

@@ -58,6 +58,12 @@ module Risc
       @symbol
     end
 
+    # can't overload "=" , so use shift for it.
+    # move the right side to the left. Left (this) is a RiscValue
+    # right value may be
+    # - constant (Parfait object) , resulting in a LoadConstant
+    # - another RiscValue, resulting in a Transfer instruction
+    # - an RValue, which gets procuced by the [] below
     def <<( load )
       puts "LOAD #{load}"
       case load
@@ -73,6 +79,22 @@ module Risc
       builder.add_instruction(ins) if builder
       return ins
     end
+
+    # just capture the values in an intermediary object (RValue)
+    # The RValue then gets used in a RegToSlot ot SlotToReg, where
+    # the values are unpacked to call Risc.reg_to_slot or Risc.slot_to_reg
+    def []( index )
+      RValue.new( self , index)
+    end
+  end
+
+  # Just a struct, see comment for [] of RiscValue
+  #
+  class RValue
+    attr_reader :register , :index
+    def initialize(register, index)
+      @register , @index = register , index
+    end
   end
 
   # The register we use to store the current message object is :r0

test/risc/test_risc_value.rb

@@ -33,5 +33,12 @@ module Risc
       @r0 << @r1
       assert_equal Transfer , builder.built.class
     end
+    def test_index_op
+      message = @r0[:first_message]
+      assert_equal RValue , message.class
+      assert_equal :first_message , message.index
+      assert_equal @r0 , message.register
+    end
+    #message << space[:first_message]
   end
 end