Retrie: Haskell refactoring made easy

Introduced Retrie, an open-source Haskell refactoring tool that allows developers to express code rewrites as equations in Haskell syntax, offering a middle ground between string manipulation and AST manipulation tools. Retrie supports rewriting expressions, types, and patterns, scripting rewrites with side conditions, and preserves local scoping and whitespace. It was used to safely migrate Sigma's rules to new APIs and libraries.