clean programming language

Clean is a general-purpose purely functional programming language. Functional languages stress application of functions, as opposed to execution of commands, as in imperative languages.

Features

Referential transparency - a function, given the same inputs, must give the same outputs.
Uniqueness typing system - easily and functionally deal with unduplicatable resources such as input and output without monads
List comprehension - compact, powerful list generation syntax
Guard statements for clear, concise conditionals
Easy-to-use Clean IDE.
Portability is almost always a simple recompile to support another platform, due to the high level of abstraction.
Automatic garbage collection - one less thing to worry about
Higher order functions and Currying
Delayed evaluation support allows infinate data structures

Examples

Hello world(Store as hello.icl):

  module hello
  Start = "Hello, world!"

Factorial:

   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 equivelent 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.

Compiling

Source files (.icl) and project files (.dcl) are converted into Clean's platform independent bytecode (.abc), implemented in C and Clean.
Bytecode is converted to object code (.obj) using C.
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.