The release notes for ghc 5.02.1 say:

1.4.4. New experimental features

Partial support for hierarchical module names.

- but I could not find a document describing how to use this feature.

Is it possible to use hierarchical module names with ghc at present, and if so, how does one write and use a hierarchically-named module ?

Module names may include the '.' character with -fglsagow-exts on. Searching for interfaces to include is extended as follows: if our search path contains directories D1...Dn, then a module A.B.C is searched for in D1/A/B/C.hi ... Dn/A/B/C.hi. You must give the full module name in the header, eg. module A.B.C where This support *is* experimental though, so it is subject to change. Also note that certain parts of the hierarchy are reserved for system-supplied libraries - see the current proposal at http://www.haskell.org/~simonmar/libraries/libraries.html Cheers, Simon