Brief introduction to Opaleye

Opaleye is a Haskell library which provides an SQL-generating embedded domain specific language for targeting Postgres. You need Opaleye if you want to use Haskell to write typesafe and composable code to query a Postgres database.

“Opaleye really is great. You’ve managed to bring what is so wonderful about relational databases and give it type safety and composition (i.e. what is wonderful about Haskell)” – Daniel Patterson, Position Development

Opaleye allows you to define your database tables and write queries against them in Haskell code, and aims to be typesafe in the sense that if your code compiles then the generated SQL query will not fail at runtime. A wide range of SQL functionality is supported including inner and outer joins, restriction, aggregation, distinct, sorting and limiting, unions and differences. Facilities to insert to, update and delete from tables are also provided. Code written using Opaleye is composable at a very fine level of granularity, promoting code reuse and high levels of abstraction.


Please get started with Opaleye by referring to these two tutorials


Contact the author

The main author of Opaleye is Tom Ellis. He can be contacted via email.

File bugs

Please file bugs on the Opaleye GitHub issue tracking page.

Mailing list

Please join the opaleye-users mailing list.

Internal modules

Opaleye exports a number of modules named Opaleye.Internal..... They are provided in case of urgent need for access to the internals, but they are not intended to be used by API consumers and if you find yourself repeatedly accessing them this is a sign that either you or Opaleye are doing something wrong. In such a case please file a bug.

The interface of Internal modules does not follow the PVP and may break between minor releases, so be careful.

Commercial support

Commercial support for Opaleye is provided by Purely Agile.


The Opaleye Project was founded by Tom Ellis, inspired by theoretical work on databases by David Spivak. Much of the implementation was based on ideas and code from the HaskellDB project by Daan Leijen, Conny Andersson, Martin Andersson, Mary Bergman, Victor Blomqvist, Bjorn Bringert, Anders Hockersten, Torbjorn Martin, Jeremy Shaw and Justin Bailey.

Silk (Erik Hesselink, Adam Bergmark), Karamaan (Christopher Lewis), Fynder (Renzo Carbonara, Oliver Charles) and Daniel Patterson contributed code to the project.

Joseph Abrahamson, Alfredo Di Napoli and Mietek Bak performed useful reviews of early versions which helped improve the codebase.


  • Use time >= 1.4 and time-locale-compat

  • Bump time to >= 1.5


  • SQL code generator escapes column names, so table column names can be the same as SQL keywords.
  • Add like operator
  • Add the types PGCitext, PGArray, PGBytea


  • Replace Default QueryRunner with a new class DefaultQueryRunnerColumn, migrate with s/Default QueryRunner/DefaultQueryRunnerColumn and s/def/queryRunnerColumnDefault/
  • Remove ShowConstant, use the monomorphic functions defined in the new module Opaleye.PGTypes instead. You will need to replace Column Bool with Column PGBool et.c. in query signatures
  • Re-export more modules from Opaleye
  • Add boolAnd, boolOr, max, and min aggregators
  • Add lower and upper
  • Add operator fixities
  • Add maybeToNullable
  • Add column instances for Bool, UUID, Text, and UTCTime
  • Expose fieldQueryRunnerColumn from Opaleye.RunQuery
  • Add unsafeCast
  • Re-export Unpackspec from Opaleye.Manipulation