lens

This package comes "Batteries Included" with many useful lenses for the types commonly used from the Haskell Platform, and with tools for au

Official docs outline

Extra Credit builds an outline of lens's docs the first time your work uses it. Until then, start at the official documentation.

mtl MTL is a collection of monad classes, extending the transformers package, using functional dependencies for generic lifting of monadic actio
unordered-containers
attoparsec A fast parser combinator library, aimed particularly at dealing efficiently with network protocols and complicated text/binary file formats.
conduit conduit is a solution to the streaming data problem, allowing for production, transformation, and consumption of streams of data in constant
QuickCheck QuickCheck is a library for random testing of program properties. The programmer provides a specification of the program, in the form of pro
random This package provides basic pseudo-random number generation, including the ability to split random number generators. In pure code, use Sys
vector . An efficient implementation of Int-indexed arrays (both mutable and immutable), with a powerful loop optimisation framework . . It is stru
dlist List-like types supporting O(1) append and snoc operations.
scientific
parsec Parsec is designed from scratch as an industrial-strength parser library. It is simple, safe, well documented (on the package homepage), ha
ansi-terminal ANSI terminal support for Haskell: allows cursor movement, screen clearing, color output, showing or hiding the cursor, and changing the tit
transformers-compat This package includes backported versions of types that were added to transformers in transformers-0.5 for users who need strict transformer