classy-prelude

A better Prelude. Haskell’s Prelude needs to maintain backwards compatibility and has many aspects that no longer represents best practice. The goals of classy-prelude are:

• remove all partial functions
• modernize data structures
  • generally use Text instead of String
  • encourage the use of appropriate data structures such as Vectors or HashMaps instead of always using lists and associated lists
• reduce import lists and the need for qualified imports

classy-prelude should only be used by application developers. Library authors should consider using mono-traversable, which classy-prelude builds upon.

It is worth noting that classy-prelude largely front-ran changes that the community made to the base Prelude in GHC 7.10.

mono-traversable

Most of this functionality is provided by mono-traversable. Please read the README over there. classy-prelude gets rid of the o prefix from mono-traversable functions.

Text

Lots of things use Text instead of String. Note that show returns a String. To get back Text, use tshow.

other functionality

• exceptions package
• system-filepath convenience functions
• whenM, unlessM
• hashNub and ordNub (efficient nub implementations).

Using classy-prelude

• use the NoImplicitPrelude extension (you can place this in your cabal file) and import ClassyPrelude
• use base-noprelude in your project and define a Prelude module that re-exports ClassyPrelude.

Appendix

• The mono-traversable README.
• The transition to the modern design of classy-prelude.

These blog posts contain some out-dated information but might be helpful

• So many preludes! (January 2013)
• ClassyPrelude: The good, the bad, and the ugly (August 2012)