classy-prelude: A typeclass-based Prelude.

[ control, library, mit, prelude ] [ Propose Tags ]

Modern best practices without name collisions. No partial functions are exposed, but modern data structures are, without requiring import lists. Qualified modules also are not needed: instead operations are based on type-classes from the mono-traversable package.

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Dependencies async, base (>=4 && <5), basic-prelude (>=0.4 && <0.7), bifunctors, bytestring, chunked-data (>=0.3), containers (>=0.4.2), deepseq, dlist (>=0.7), exceptions (>=0.5), ghc-prim, hashable, lifted-async (>=0.3), lifted-base (>=0.2), monad-unlift (>=0.2), mono-traversable (>=1.0), mono-traversable-instances, mtl, mutable-containers (>=0.3 && <0.4), primitive, safe-exceptions (>=0.1.1), say, semigroups, stm (<2.5), stm-chans (>=3), text, time, time-locale-compat, transformers, transformers-base, unordered-containers, vector, vector-instances [details]
License MIT
Author Michael Snoyman
Revised Revision 1 made by HerbertValerioRiedel at 2018-10-05T23:42:20Z
Category Control, Prelude
Home page
Source repo head: git clone
Uploaded by MichaelSnoyman at 2017-01-22T09:30:12Z
Distributions Arch:, Debian:1.5.0, FreeBSD:, LTSHaskell:, NixOS:, Stackage:
Reverse Dependencies 57 direct, 152 indirect [details]
Downloads 80403 total (244 in the last 30 days)
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Status Docs available [build log]
Last success reported on 2017-01-22 [all 1 reports]

Readme for classy-prelude-1.2.0

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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 Haskell's Prelude needs to maintain backwards compatibility and has many aspects that no longer represents best practice.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.


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.


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.


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