Clean (programming language)

Clean (programming language)

In computer science, Clean is a general-purpose purely functional computer programming language.



Hello world (Store as hello.icl):

module hello
Start = "Hello, world!"


 module factorial
 fac 0 = 1
 fac n = n * fac (n-1)

 // find the factorial of 10
 Start = fac 10

Fibonacci sequence:

 module fibonacci
 fib 0 = 0
 fib 1 = 1
 fib n = fib (n - 2) + fib (n - 1) 
 Start = fib 7

Infix operator:

 (^) infixr 8 :: Int Int -> Int
 (^) x 0 = 1
 (^) x n = x * x ^ (n-1)

The type declaration states that the function is a right associative infix operator with priority 8: this states that x*x^(n-1) is equivalent to x*(x^(n-1)) as opposed to (x*x)^(n-1); this operator is pre-defined in the Clean standard environment.

How Clean works

Computation is based on graph rewriting and reduction. Constants such as numbers are graphs and functions are graph rewriting formulas. This, combined with compilation to native code, makes Clean programs relatively fast, even with high abstraction.


  1. Source files (.icl) and project files (.dcl) are converted into Clean's platform-independent bytecode (.abc), implemented in C and Clean.
  2. Bytecode is converted to object code (.obj) using C.
  3. object code is linked with other files in the module and the runtime system and converted into a normal executable in Clean.

Earlier Clean system versions were written completely in C, thus avoiding bootstrapping issues.


Clean is available for Microsoft Windows. It is also available with limited input/output capabilities and without the "Dynamics" feature for Apple Macintosh, Solaris and Linux.


Clean is dual licensed: it is available under the terms of the GNU LGPL, and also under a proprietary license.


See also

External links

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