The esqueleto EDSL (embedded domain specific language) for SQL queries which replaces Database.Persist
esqueleto is a bare bones, type-safe EDSL for SQL queries that works with unmodified persistent SQL backends. Its language closely resembles SQL, so (a) you don't have to learn new concepts, just new syntax, and (b) it's fairly easy to predict the generated SQL and optimize it for your backend. Most kinds of errors committed when writing SQL are caught as compile-time errors---although it is possible to write type-checked esqueleto queries that fail at runtime.
persistent is a library for type-safe data serialization. It has many kinds of backends, such as SQL backends (persistent-mysql, persistent-postgresql, persistent-sqlite) and NoSQL backends (persistent-mongoDB).
While persistent is a nice library for storing and retrieving records, currently it has a poor interface for SQL backends compared to SQL itself. For example, it's extremely hard to do a type-safe JOIN on a many-to-one relation, and simply impossible to do any other kinds of JOINs (including for the very common many-to-many relations). Users have the option of writing raw SQL, but that's error prone and not type-checked.
The name of this library means "skeleton" in Portuguese and contains all three SQL letters in the correct order =). It was inspired by Scala's Squeryl but created from scratch.
Taken from the HackageDB site
