Pure, lazy, statically typed functional language (1990). Every expression is referentially transparent; effects are confined to the type system via monads. The premier industrial vehicle for type-system research.
Key facts
Year: 1990; committee design from FPCA community.
Paradigm: pure functional, lazy.
Typing: static, strong, Hindley-Milner + type classes (System Fω under GHC).
Memory: garbage-collected; closures and thunks heap-allocated.