Haskell is the world's leading lazy functional programming language, widely used for teaching, research, and applications. The language continues to develop rapidly, but in 1998 the community decided to capture a stable snapshot of the language: Haskell 98. All Haskell compilers support Haskell 98, so practitioners and educators alike have a stable base for their work.This book constitutes the agreed definition of Haskell 98, both the language itself and its supporting libraries, and should be a standard reference work for anyone involved in research, teaching, or application of Haskell.