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Clean is a general purpose, state-of-the-art, pure and lazy functional 
programming language designed for making real-world applications.
Here is a list of the most notable language features:

* Clean is a lazy, pure, and higher-order functional programming language with explicit graph-rewriting semantics. 

* Although Clean is by default a lazy language, one can smoothly turn it into a strict language to obtain optimal time/space behavior: functions can be defined lazy as well as (partially) strict in their arguments; any (recursive) data structure can be defined lazy as well as (partially) strict in any of its arguments.

* Clean is a strongly typed language based on an extension of the well-known Milner/Hindley/Mycroft type inferencing/checking scheme including the common higher-order types, polymorphic types, abstract types, algebraic types, type synonyms, and existentially quantified types.

* Clean has pattern matching, guards, list comprehensions, array comprehensions and a lay-out sensitive mode.

* Clean supports type classes and type constructor classes to make overloaded use of functions and operators possible.

* The uniqueness typing system of Clean makes it possible to develop efficient applications. In particular, it allows a refined control over the single-threaded use of objects which can influence the time and space behavior of programs. Uniqueness typing can also be used to incorporate destructive updates of objects within a pure functional framework. It allows destructive transformation of state information and enables efficient interfacing to the nonfunctional world (to C but also to I/O systems like X-Windows) offering direct access to file systems and operating systems.

* Clean offers records and (destructively updateable) arrays and files.

* The Clean type system supports dynamic types, allowing values of arbitrary types to be wrapped in a uniform package and unwrapped via a type annotation at run time. Using dynamics, code and data can be exchanged between Clean applications in a flexible and type-safe way.

* Clean provides a built-in mechanism for generic functions.

* There is a Clean IDE and there are many [[libraries]] available offering additional functionality.