Yes, locally-bound uniques change all the time, to maintain scoping hygiene. But top-level things from other modules have uniques that do not change. simon From: ghc-devs-bounces@haskell.org [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Edsko de Vries Sent: 26 March 2013 15:05 To: ghc-devs@haskell.org Subject: Stability of Uniques Hi all, Consider the very simple test module Test2 where f = True When walking the AST after renaming I see that f has unique 1912603236 and True has unique 905969694. However, when walking the typechecked AST f seems to have unique 1627390565 instead. Should I expect that the unique associated with identifiers changes between renaming and typechecking? Or is there something else that I'm missing? Thanks! Edsko