Add :add keyword and implementation

compile_arithmetic.rb

@@ -0,0 +1,15 @@
+
+# Method to compile arithmetic
+class Compiler
+
+  def compile_add(scope, left, right)
+    @e.with_register do |reg|
+      src = compile_eval_arg(scope,left)
+      @e.movl(src,reg)
+      @e.save_result(compile_eval_arg(scope,right))
+      @e.addl(reg, :eax)
+    end
+    [:subexpr]
+  end
+
+end

compiler.rb

@@ -10,6 +10,8 @@
 require 'set'
 require 'print_sexp'
 
+require 'compile_arithmetic'
+
 class Compiler
   attr_reader :global_functions
   attr_accessor :trace
@@ -21,7 +23,7 @@ class Compiler
                    :do, :class, :defun, :defm, :if, :lambda,
                    :assign, :while, :index, :let, :case, :ternif,
                    :hash, :return,:sexp, :module, :rescue, :incr, :block,
-                   :required
+                   :required, :add
                   ]
 
   Keywords = @@keywords