DSH-0.10.0.1: README.md

# Database-Supported Haskell (DSH)

This is a Haskell library for database-supported program execution. Using
this library a relational database management system (RDBMS) can be used as
a coprocessor for the Haskell programming language, especially for those
program fragments that carry out data-intensive and data-parallel
computations.

Database executable program fragments can be written using the monad
comprehension notation [2] and list processing combinators from the Haskell
list prelude. Note that rather than embedding a relational language into
Haskell, we turn idiomatic Haskell programs into SQL queries.

DSH faithfully represents list order and nesting, and compiles the list
processing combinators into relational queries. The implementation avoids
unnecessary data transfer and context switching between the database
coprocessor and the Haskell runtime by ensuring that the number of generated
relational queries is only determined by the program fragment's type and not
by the database size.

DSH can be used to allow existing Haskell programs to operate on large scale
data (e.g., larger than the available heap) or query existing database
resident data with Haskell.

Note that this package is flagged experimental and therefore is not suited
for production use. This is a proof of concept implementation only. To learn
more about DSH, our paper entitled as "Haskell Boards the Ferry: Database-
Supported Program Execution for Haskell" [1] is a recommended reading. The
package includes a couple of examples that demonstrate how to use DSH.

In contrast to the DSH version described in [1], the current release
does not rely anymore on the loop-lifting compilation technique
together with the Pathfinder optimizer. Instead, it brings a
completely rewritten query compiler based on Guy Blelloch's flattening
transformation. This approach leads to a more robust compilation and
produces more efficient query code.

1. [http://db.inf.uni-tuebingen.de/staticfiles/publications/ferryhaskell.pdf](Grust
   et al. Haskell Boards the Ferry. Database-Supported Program
   Execution for Haskell. IFL 2010)
2. [http://db.inf.uni-tuebingen.de/staticfiles/publications/haskell2011.pdf](Grust
   et al. Bringing Back Monad Comprehensions. Haskell Symposium 2011).

# Release Notes

* This is an experimental proof-of-concept implementation that most
  likely contains bugs. You have been warned. We are happy to receive
  bug reports.
* For documentation, have a look at the examples included in directory
  'examples' in the source distribution.
* DSH works with a HDBC PostgreSQL connection. Other databases (*e.g.*
  MySQL, Sqlite) are unlikely to work.
* Support for general algebraic data types is currently broken. Flat
  record types do work.
* Comprehension syntax for DSH queries is currently implemented using
  monad comprehensions and the `RebindableSyntax` extension. This
  means that any module that contains DSH queries and makes use of
  comprehension syntax has to enable the extension. Additionally,
  `do`-notation and comprehensions over other monads (*e.g.* lists)
  can not be used in such a module. This limitation is an
  implementation artifact that we hope to get rid of soon.