BSD-3-Clause licensed by Ralf Lammel, Simon Peyton Jones, Jose Pedro Magalhaes
Maintained by Sergey Vinokurov
This version can be pinned in stack with:syb-,3872

syb: Scrap Your Boilerplate!

Scrap Your Boilerplate (SYB) is a library for generic programming in Haskell. It is supported since the GHC >= 6.0 implementation of Haskell. Using this approach, you can write generic functions such as traversal schemes (e.g., everywhere and everything), as well as generic read, generic show and generic equality (i.e., gread, gshow, and geq). This approach is based on just a few primitives for type-safe cast and processing constructor applications.

It was originally developed by Ralf Lämmel and Simon Peyton Jones. Since then, many people have contributed with research relating to SYB or its applications.

More information is available on the webpage:


  • Easy generic programming with combinators
  • GHC can derive Data and Typeable instances for your datatypes
  • Comes with many useful generic functions


  • GHC 6.10.1 or later
  • Cabal 1.6 or later

Bugs & Support

Please report issues or request features at the bug tracker:

For discussion about the library with the authors, maintainers, and other interested persons use the mailing list:


  • Improved documentation (thanks to @BinderDavid)
  • Export ext2 function which was already defined but not exported

  • Compatibility with mtl 2.3 and GHC 9.6

  • Compatibility with GHC 9.4

  • Update cabal version


  • Add compatibility with GHC 9, switch to tasty for tests, fix tests on GHCJS


  • Define recursive traversals in two parts, non-recursive wrapper and recursive local helper to facilitate inlining and avoid passing the same argument to all recursive calls