move compiler into virtual

and associated changes in code, requires tests etc

lib/virtual/compiler.rb

@@ -0,0 +1,44 @@
+module Virtual
+  module Compiler
+
+    # Compiling is the conversion of the AST into 2 things:
+    # - code (ie sequences of Instructions inside Blocks) carried by CompiledMethods
+    # - an object graph containing all the Methods, their classes and Constants
+    #
+    # Some compile methods just add code, some may add structure (ie Blocks) while
+    # others instantiate Class and Method objects
+    #
+    # Everything in ruby is an expression, ie returns a value. So the effect of every compile
+    # is that a value is put into the ReturnSlot of the current Message.
+    # The compile method (so every compile method) returns the value that it deposits which
+    # may be unknown Mystery value.
+    #
+    # The Compiler.compile uses a visitor patter to dispatch according to the class name of
+    # the expression. So a NameExpression is delegated to compile_name etc.
+    # This makes the dispatch extensible, ie Expressions may be added by external code,
+    # as long as matching compile methods are supplied too.
+    #
+    def self.compile expression , method
+      exp_name = expression.class.name.split("::").last.sub("Expression","").downcase
+      #puts "Expression #{exp_name}"
+      begin
+        self.send "compile_#{exp_name}".to_sym , expression, method
+      rescue NoMethodError => e
+        puts "No compile method found for " + exp_name
+        raise e
+      end
+    end
+
+  end
+end
+
+require_relative "compiler/basic_expressions"
+require_relative "compiler/callsite_expression"
+require_relative "compiler/compound_expressions"
+require_relative "compiler/if_expression"
+require_relative "compiler/function_expression"
+require_relative "compiler/module_expression"
+require_relative "compiler/operator_expressions"
+require_relative "compiler/return_expression"
+require_relative "compiler/while_expression"
+require_relative "compiler/expression_list"