Hello Haskell-Café, I am happy to announce the [Express] library for Haskell. https://github.com/rudymatela/express Express allows manipulation of dynamically typed Haskell expressions. It is similar to Data.Dynamic but with support for encoding applications and variables. It provides an Expr type and over a hundred functions for building, evaluating, comparing, folding, canonicalizing and matching Exprs. [Express' Haddock documentation] is pretty comprehensive. The project [README] has a few examples showing how to use Express to: * create heterogeneous lists; * list valid applications between expressions; * generalize counterexamples; * automatically generate test properties. This library has its origins as an internal module of [Speculate] and [Extrapolate], I am now releasing it separetely hoping that it could be used for other purposes. To install it, just: $ cabal update $ cabal install express Then you're ready to use it: $ ghci > import Data.Express > let true = val True > :t true true :: Expr > print true True :: Bool > eval False true True -- Rudy [Express]: https://github.com/rudymatela/express [Express' Haddock documentation]: https://hackage.haskell.org/package/express/docs/Data-Express.html [README]: https://github.com/rudymatela/express#readme [Speculate]: https://github.com/rudymatela/speculate [Extrapolate]: https://github.com/rudymatela/extrapolate