th-to-exp is a package that provides a way to persist data from compile-time to runtime by producing Template Haskell expressions that evaluate to particular values. For example, if you have a value Just 1, then toExp (Just 1) will produce the expression [e| Just 1 |], which can be used in a splice. For a more direct example, here’s what that looks like without the quasiquote notation:
> toExp (Just 1)
AppE (ConE GHC.Base.Just) (LitE (IntegerL 1))This is done by using a typeclass, ToExp, that can be automatically derived for types that have a Generic instance.