slightly better messages for unsupported ruby

Very slightly unfortunately, just just enought to find the error.
Also testing what is unsupported, so it's documented.

lib/ruby/ruby_compiler.rb

@@ -1,4 +1,19 @@
 module Ruby
+  class ProcessError < Exception
+    attr_reader :node
+
+    def initialize(msg , node)
+      super(msg)
+      @node = node
+    end
+    def message
+      super + node_tos
+    end
+    def node_tos
+      return "" unless @node
+      @node.to_s[0 ... 200]
+    end
+  end
   # This RubyCompiler compiles incoming ruby (string) into a typed
   # version of theast, with the help of the parser gem.
   # The parser outputs an abstract ast (nodes)
@@ -10,16 +25,22 @@ module Ruby
   # simpler, and then finally to compile
   # to the next level down, MOM (Minimal Object Machine)
   class RubyCompiler < AST::Processor
-  include AST::Sexp
+    include AST::Sexp
 
     def self.compile(input)
       ast = Parser::Ruby22.parse( input )
       self.new.process(ast)
     end
 
+    # raise a ProcessError. This means ruby-x doesn't know how to handle it.
+    # Parser itself throws SyntaxError
+    def not_implemented(node)
+      raise ProcessError.new("Not implemented #{node.type}", node)
+    end
+
     # default to error, so non implemented stuff shows early
     def handler_missing(node)
-      raise "Not implemented #{node.type} #{node}"
+      not_implemented(node)
     end
 
     def on_class( statement )
@@ -83,8 +104,8 @@ module Ruby
     end
     alias  :on_string :on_str
 
-    def on_dstr expression
+    def on_dstr( expression )
-      raise "Not implemented dynamic strings (with interpolation)"
+      not_implemented(expression)
     end
     alias  :on_xstr :on_dstr
 
@@ -93,8 +114,8 @@ module Ruby
     end
     alias  :on_string :on_str
 
-    def on_dsym
+    def on_dsym(expression)
-      raise "Not implemented dynamix symbols (with interpolation)"
+      not_implemented(expression)
     end
     def on_kwbegin statement
       ScopeStatement.new process_all( statement.children )
@@ -131,7 +152,7 @@ module Ruby
     def on_const expression
       scope = expression.children.first
       if scope
-        raise "Only unscoped Names implemented #{scope}" unless scope.type == :cbase
+        not_implemented(expression) unless scope.type == :cbase
       end
       ModuleName.new(expression.children[1])
     end
@@ -213,7 +234,7 @@ module Ruby
     end
 
     def handler_missing(node)
-      raise "Handler missing #{node}"
+      not_implemented(node)
     end
 
     private

test/ruby/test_basic_values.rb

@@ -33,8 +33,8 @@ module Ruby
       assert_equal SymbolConstant , lst.class , lst.inspect
     end
     def test_dstr
-      assert_raises RuntimeError do
+      assert_raises Ruby::ProcessError do
-        compile( '"dstr#{self}"')
+        compile( '"interpolate #{self}"')
       end
     end
 

test/ruby/test_not_implemented.rb

@@ -0,0 +1,20 @@
+require_relative "helper"
+
+module Ruby
+  class NotImplemented < Minitest::Test
+    include RubyTests
+
+    def assert_handler_missing(input)
+      assert_raises(Ruby::ProcessError){ compile(input) }
+    end
+
+    def test_module
+      assert_handler_missing "module Name ; end"
+    end
+
+    def test_module_module_scoped
+      assert_handler_missing( "M::Module" )
+    end
+
+  end
+end

test/ruby/test_variables.rb

@@ -51,9 +51,6 @@ module Ruby
       assert_equal ModuleName , lst.class
       assert_equal :Module , lst.name
     end
-    def test_module_module_scoped
-      assert_raises {compile( "M::Module" ) }
-    end
   end
   class TestVariablesVool < MiniTest::Test
     include RubyTests