rename also get_slot, to slot_to_reg

makes source and target clear

lib/register/instructions/slot_to_reg.rb

@@ -0,0 +1,34 @@
+module Register
+
+  # SlotToReg moves data into a register from memory.
+  # RegToSlot moves data into memory from a register.
+  # Both use a base memory (a register)
+
+  # This is because that is what cpu's can do. In programming terms this would be accessing
+  #  an element in an array, in the case of SlotToReg setting the value in the array.
+
+  # btw: to move data between registers, use RegisterTransfer
+
+  class SlotToReg < Getter
+
+    # If you had a c array and index offset
+    # the instruction would do register = array[index]
+    # The arguments are in the order that makes sense for the Instruction name
+    # So SlotToReg means the slot (array and index) moves to the register (last argument)
+    # def initialize source , array , index , register
+    #   super
+    # end
+    # attr_accessor :array , :index , :register
+
+  end
+
+  # Produce a SlotToReg instruction.
+  # Array and to are registers or symbols that can be transformed to a register by resolve_to_register
+  # index resolves with resolve_index.
+  def self.slot_to_reg source , array , index , to
+    index = resolve_index( array , index)
+    array = resolve_to_register array
+    to = resolve_to_register to
+    SlotToReg.new( source , array , index , to)
+  end
+end