Hi I started to check the cs for the closure changes. Here is the list of points for the file-compiler preload. Here are the changes to look at: - Changes in classBuilder computeFormat: type instSize: newInstSize forSuper: newSuper ccIndex: ccIndex superclass: aClass variableByteSubclass: t instanceVariableNames: f classVariableNames: d poolDictionaries: s category: cat - MessageNode checkBlock: node as: nodeName from: encoder maxArgs: maxArgs - MethodNode rawSourceRanges - Parser encoder pattern: fromDoit inContext: ctxt Stef