Haskell Hierarchical Libraries

The libraries are divided into several packages. NOTE: there is not always a clean division between packages in the hierarchy, which means a node and its children might be in different packages. If you're looking for a specific module, try all the packages below.

base: the Prelude, and a large collection of useful libraries.
haskell98: Haskell 98 and FFI Standard Libraries.
haskell-src: manipulating Haskell source code.
network: networking support libraries.
parsec: monadic parser combinators.
QuickCheck: automatic specification-based testing.
readline: a library for interactively reading input from the console.
unix: supplies POSIX functionality.
OpenGL: 3D rendering.
GLUT: the OpenGL utility toolkit.
ObjectIO: GUI library.

Implementation-specific notes

GHC/GHCi: Most of the time, all the packages are available without the need to use any additional command-line options. The only time when this is not the case is when linking a program on the command line, without using the --make option: in this case you must list all the packages to link to by adding the -package P flag (where P is the package name) to the command line for each package. See the User's Guide for more details.
Hugs 98: Hugs provides almost all of the modules in the base package and all the modules in the haskell98, haskell-src, network, parsec and QuickCheck packages. @unixHTMLStart@ Most of the modules in the unix package are supported, too. @unixHTMLEnd@ @HOpenGLHTMLStart@ If the target platform supports OpenGL, the OpenGL and GLUT packages are supported too. @HOpenGLHTMLEnd@ All those modules are always available, as a single hierarchy; Hugs does not use the package subdivision.
Nhc98: The modules of the haskell98 package are available without the need to use any additional compile-time options. To use modules from some other package P with Nhc98, add the compile-time option -package P. Nhc98 currently provides many of the modules in the base package (see the Nhc98 libraries page for a list).