vendored parslet, deemed stable enough and better without dependency

lib/parslet/atoms/entity.rb

@@ -0,0 +1,41 @@
+# This wraps pieces of parslet definition and gives them a name. The wrapped
+# piece is lazily evaluated and cached. This has two purposes: 
+#     
+# * Avoid infinite recursion during evaluation of the definition
+# * Be able to print things by their name, not by their sometimes
+#   complicated content.
+#
+# You don't normally use this directly, instead you should generated it by
+# using the structuring method Parslet.rule.
+#
+class Parslet::Atoms::Entity < Parslet::Atoms::Base
+  attr_reader :name, :block
+  def initialize(name, &block)
+    super()
+    
+    @name = name
+    @block = block
+  end
+
+  def try(source, context, consume_all)
+    parslet.apply(source, context, consume_all)
+  end
+  
+  def parslet
+    @parslet ||= @block.call.tap { |p| 
+      raise_not_implemented unless p
+    }
+  end
+
+  def to_s_inner(prec)
+    name.to_s.upcase
+  end  
+private 
+  def raise_not_implemented
+    trace = caller.reject {|l| l =~ %r{#{Regexp.escape(__FILE__)}}} # blatantly stolen from dependencies.rb in activesupport
+    exception = NotImplementedError.new("rule(#{name.inspect}) { ... }  returns nil. Still not implemented, but already used?")
+    exception.set_backtrace(trace)
+    
+    raise exception
+  end
+end