Hey! :) I've just released the first major bump of esqueleto in a long time. This was needed in order to change the signatures of all functions that took IsString arguments to the new SqlString type class. Now you can make your newtypes instances of SqlString without bothering with IsString. And, finally, Maybe is an instance of SqlString, so string-related functions will work with nullable types out-of-the-box. If you had a custom IsString instance previously, you may now need to make it an instance of SqlString as well: instance SqlString FooBar where -- This is not a typo, there are no class methods. If you had generic functions that took a data type that implements IsString, you may need to change them to SqlString. Your code should otherwise work fine without any changes. Cheers, PS: Shhhh, just ignore esqueleto-2.3.0. :) -- Felipe.