Hugs 98 is a functional programming system based on Haskell 98, the
de facto standard for non-strict functional programming languages.

Hugs 98 provides an almost complete implementation of Haskell 98,
including monad and record syntax, newtypes, strictness annotations,
and modules. In addition, it comes packaged with almost all libraries
defined in the most recent version of the Haskell 98 Library Report.

Hugs 98 also supports a number of advanced and experimental extensions
including multi-parameter classes, extensible records, rank-2
polymorphism, existentials, scoped type variables, and restricted
type synonyms.

WWW: http://www.haskell.org/hugs/