I have data objects where each component is a labelled field through which I access or modify it. I have a hierarchy of these - many of the fields are themselves such data objects, so I may need to apply a few selector functions to get down to what I want (call these "deep"). For fairly flat things, the updates using field labels are okay. However, when I have a function that needs to tweak various bits of various "deep" fields, based on various conditions, then it gets really ugly, not least because of the conditions: foo { bar = baz } becomes, let old = bar foo in foo { bar = if cond then f old else old } or whatever. Do I need such a let for each component and sub-component of the object that has a child that may be modified, or will foo { bar = if cond then f (bar foo) else bar foo } be suitably optimised? (The if's inside the {} because there may be multiple fields (or children thereof) being modified based on different conditions.) -- Mark