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Clean (programming language)#Examples

{{Short description|Functional programming language}}

{{Use dmy dates|date=March 2023}}

{{Infobox programming language

| name = Clean

| logo = Clean 3.0 (programming language) logo.svg

| paradigm = functional

| designer = Software Technology Research Group of Radboud University Nijmegen

| released = {{Start date and age|1987}}

| latest release version = 3.1

| latest release date = {{Start date and age|2022|01|05|df=yes}}

| typing = strong, static, dynamic

| operating system = Cross-platform

| license = Simplified BSD{{cite web |title=Download Clean |url=https://clean.cs.ru.nl/Download_Clean#Clean_3.0_License |website=Clean |access-date=23 July 2019}}

| influenced by = [https://foldoc.org/Lean Lean], Miranda, Haskell

| influenced = Haskell, Idris{{cite web|title=Idris - Uniqueness Types|url=http://docs.idris-lang.org/en/latest/reference/uniqueness-types.html|access-date=2018-11-20}}

| file_ext = .icl, .dcl, .abc

| website = {{URL|clean.cs.ru.nl}}

}}

Clean is a general-purpose purely functional programming language. Originally called the Concurrent Clean System{{cite web |url=https://ftp.cs.ru.nl/Clean/old/Clean07/Sun4/README |title=Clean 0.7: Readme |archive-url=https://web.archive.org/web/20190524121044/https://ftp.cs.ru.nl/Clean/old/Clean07/Sun4/README |archive-date=2019-05-24}} or the Clean System,{{cite web |url=https://ftp.cs.ru.nl/Clean/old/Clean10/README |title=Clean 1.0: Readme |archive-url=https://web.archive.org/web/20190505113256/https://ftp.cs.ru.nl/Clean/old/Clean10/README |archive-date=2019-05-05}}{{cite web |url=https://ftp.cs.ru.nl/Clean/Clean13/README |title=Clean 1.3: Readme |archive-url=https://web.archive.org/web/20190427194714/https://ftp.cs.ru.nl/Clean/Clean13/README |archive-date=2019-04-27}} it has been developed by a group of researchers from the Radboud University in Nijmegen since 1987.{{cite web |url=https://www.mbsd.cs.ru.nl/Software |title=Radboud University Nijmegen: Department of Software Science: Software}}{{cite web |url=http://wiki.clean.cs.ru.nl/FAQ |access-date=2021-11-26 |title=FAQ |website=Clean}} Although development of the language has slowed, some researchers are still working in the language.{{cite web |url=https://clean.cs.ru.nl/Publications |access-date=2021-11-26 |title=Publications |website=Clean}} In 2018, a spin-off company was founded that uses Clean.{{cite web |url=https://www.top-software.nl/ |title=Home |website=TOP Software Technology |access-date=26 November 2021}}

Features

Clean shares many properties and syntax with a younger sibling language, Haskell: referential transparency, list comprehension, guards, garbage collection, higher order functions, currying, and lazy evaluation. However, Clean deals with mutable state and input/output (I/O) through a uniqueness type system, in contrast to Haskell's use of monads. The compiler takes advantage of the uniqueness type system to generate more efficient code, because it knows that at any point during the execution of the program, only one reference can exist to a value with a unique type. Therefore, a unique value can be changed in place.ftp://ftp.cs.ru.nl/pub/Clean/papers/2007/achp2007-CleanHaskellQuickGuide.pdf

An integrated development environment (IDE) for Microsoft Windows is included in the Clean distribution.

Examples

Hello world:

Start = "Hello, world!"

Factorial:

valign="bottom"

|

fac :: Int -> Int

fac 0 = 1

fac n = n * fac (n-1)

Start = fac 10

|

fac :: Int -> Int

fac n = prod [1..n] // The product of the numbers 1 to n

Start = fac 10

Fibonacci sequence:

valign="bottom"

|

fib :: Int -> Int

fib 0 = 1

fib 1 = 1

fib n = fib (n - 2) + fib (n - 1)

Start = fib 7

|

fibs :: Int Int -> [Int]

fibs x_2 x_1 = [x_2:fibs x_1 (x_2 + x_1)]

fib :: Int -> Int

fib n = (fibs 1 1) !! n

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 StdEnv, the Clean standard library.

How Clean works

Computing is based on graph rewriting and reduction. Constants such as numbers are graphs and functions are graph rewriting formulas. This, combined with compiling to native code, makes Clean programs which use high abstraction run relatively fast according to The Computer Language Benchmarks Game.{{cite web |title=Which programming languages are fastest? |url=http://shootout.alioth.debian.org/u32/which-programming-languages-are-fastest.php |website=Computer Language Benchmarks Game |url-status=bot: unknown |archive-url=https://web.archive.org/web/20110628185627/http://shootout.alioth.debian.org/u32/which-programming-languages-are-fastest.php |archive-date=28 June 2011}} A 2008 benchmark showed that Clean native code performs similarly to the Glasgow Haskell Compiler (GHC), depending on the benchmark.{{cite journal |last1=Jansen |first1=Jan Martin |last2=Koopman |first2=Pieter |last3=Plasmeijer |first3=Rinus |date=2008 |title=From Interpretation to Compilation |url=ftp://ftp.cs.ru.nl/pub/Clean/papers/2008/janj08-CEFP07-InterpretationToCompilation.pdf |access-date=2016-05-21}}

Compiling

Compilation of Clean to machine code is performed as follows:

  1. Source files (.icl) and definition files (.dcl) are translated into Core Clean, a basic variant of Clean, by the compiler frontend written in Clean.
  2. Core clean is converted into Clean's platform-independent intermediate language (.abc), by the compiler backend written in Clean and C.
  3. Intermediate ABC code is converted to object code (.o) by the code generator written in C.
  4. Object code is linked with other files in the module and the runtime system and converted into a normal executable using the system linker (when available) or a dedicated linker written in Clean on Windows.

Earlier versions of the Clean compiler were written completely in C, thus avoiding bootstrapping issues.

= The ABC machine =

The ABC code mentioned above is an intermediate representation for an abstract machine. Because machine code generation for ABC code is relatively straightforward, it is easy to support new architectures. The ABC machine is an imperative abstract graph rewriting machine.{{cite thesis|type=PhD|last1=Koopman|first1=Pieter|title=Functional Programs as Executable Specifications|date=10 December 1990|publisher=Katholieke Universiteit Nijmegen|isbn=90-9003689-X|page=35}} It consists of a graph store to hold the Clean graph that is being rewritten and three stacks:

  • The A(rgument)-stack holds arguments that refer to nodes in the graph store.
  • The B(asic value)-stack holds basic values (integers, characters, reals, etc.). Although these values could be nodes in the graph store, a separate stack is used for efficiency.
  • The C(ontrol)-stack holds return addresses for flow control.

The runtime system, which is linked into every executable, builds a Start node in the graph store and pushes it on the A-stack. It then begins printing it, evaluating it as needed.

= Running Clean in the browser =

Although Clean is typically used to generate native executables, several projects have enabled applications in web browsers.

The now abandoned [https://clean.cs.ru.nl/SAPL SAPL] project compiled Core Clean to JavaScript and did not use ABC code. Since 2019, an interpreter for ABC code, written in WebAssembly, is used instead.{{cite web |title=Clean and iTasks / ABC Interpreter · GitLab |url=https://gitlab.com/clean-and-itasks/abc-interpreter |website=Clean and iTasks on GitLab |access-date=13 April 2023 |language=en}}{{cite book |last1=Staps |first1=Camil |last2=van Groningen |first2=John |last3=Plasmeijer |first3=Rinus |title=Proceedings of the 31st Symposium on Implementation and Application of Functional Languages |chapter=Lazy interworking of compiled and interpreted code for sandboxing and distributed systems |date=15 July 2021 |pages=1–12 |doi=10.1145/3412932.3412941|isbn=9781450375627 |s2cid=202751977 }}

Platforms

Clean is available for Microsoft Windows (IA-32 and X86-64), macOS (X86-64), and Linux (IA-32, X86-64, and AArch64).{{citation needed|date=September 2023}}

Some libraries are not available on all platforms, like ObjectIO which is only available on Windows. Also the feature to write dynamics to files is only available on Windows.{{citation needed|date=September 2023}}

The availability of Clean per platform varies with each version:{{cite web |title=Release history |url=https://clean.cs.ru.nl/Release_history |website=Clean |access-date=7 January 2022}}{{cite web |title=Index of /Clean |url=https://ftp.cs.ru.nl/Clean/ |access-date=7 January 2022}}

class="wikitable sortable"
rowspan=2 | Version

! rowspan=2 | Date

! colspan=3 | Linux

! colspan=3 | macOS

! Oracle Solaris

! colspan=2 | Windows

! rowspan=2 | Miscellaneous

IA-32

! x86-64

! AArch64

! Motorola 68040

! PowerPC

! x86-64

! SPARC

! IA-32

! x86-64

3.1{{Date table sorting|5 January 2022}}

| {{Yes}}

{{Yes}}{{Yes}}

| {{No}}

{{No}}{{Yes}}

| {{No}}

| {{Yes}}

{{Yes}}

|

3.0{{Date table sorting|2 October 2018}}

| {{Yes}}

{{Yes}}{{No}}

| {{No}}

{{No}}{{Yes}}

| {{No}}

| {{Yes}}

{{Yes}}

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2.4{{Date table sorting|23 December 2011}}

| {{Yes}}

{{Yes}}{{No}}

| {{No}}

{{No}}{{Yes}}

| {{No}}

| {{Yes}}

{{Yes}}

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2.3{{Date table sorting|22 December 2010}}

| {{Yes}}

{{Yes}}{{No}}

| {{No}}

{{No}}{{No}}

| {{No}}

| {{Yes}}

{{Yes}}

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2.2{{Date table sorting|19 December 2006}}

| {{Yes}}

{{Yes}}{{No}}

| {{No}}

{{Yes}}{{No}}

| {{Yes}}

| {{Yes}}

{{Yes}}

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2.1.1{{Date table sorting|31 May 2005}}

| {{Yes}}

{{No}}{{No}}

| {{No}}

{{Yes}}{{No}}

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| {{Yes}}

{{No}}

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2.1.0{{Date table sorting|31 October 2003}}

| {{Yes}}

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2.0.2{{Date table sorting|12 December 2002}}

| {{Yes}}

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2.0.1{{Date table sorting|4 July 2002}}

| {{Yes}}

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2.0{{Date table sorting|21 December 2001}}

| {{No}}

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1.3.3{{Date table sorting|13 September 2000}}

| {{Yes}}

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1.3.2{{Date table sorting|1 July 1999}}

| {{No}}

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1.3.1{{Date table sorting|January 1999}}

| {{Yes}}

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| {{No}}

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1.3{{Date table sorting|22 May 1998}}

| {{Yes}}

{{No}}{{No}}

| {{No}}

{{Yes}}{{No}}

| {{Yes}}

| {{Yes}}

{{No}}

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1.2.4{{Date table sorting|June 1997}}

| {{No}}

{{No}}{{No}}

| {{Yes}}

{{Yes}}{{No}}

| {{No}}

| {{Yes}}

{{No}}

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1.2.3{{Date table sorting|May 1997}}

| {{No}}

{{No}}{{No}}

| {{Yes}}

{{Yes}}{{No}}

| {{No}}

| {{Yes}}

{{No}}

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1.2{{Date table sorting|13 January 1997}}

| {{No}}

{{No}}{{No}}

| {{Yes}}

{{Yes}}{{No}}

| {{No}}

| {{No}}

{{No}}

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1.1.3{{Date table sorting|October 1996}}

| {{No}}

{{No}}{{No}}

| {{No}}

{{No}}{{No}}

| {{Yes}}

| {{No}}

{{No}}

| OS/2 (i80386)

1.1.2{{Date table sorting|September 1996}}

| {{Yes}}

{{No}}{{No}}

| {{No}}

{{No}}{{No}}

| {{Yes}}

| {{No}}

{{No}}

| SunOS 4 (SPARC)

1.1{{Date table sorting|March 1996}}

| {{Yes}}

{{No}}{{No}}

| {{Yes}}

{{No}}{{No}}

| {{No}}

| {{No}}

{{No}}

|

1.0.2{{Date table sorting|September 1995}}

| {{Yes}}

{{No}}{{No}}

| {{Yes}}

{{No}}{{No}}

| {{Yes}}

| {{No}}

{{No}}

| OS/2 (i80386); SunOS 4 (SPARC)

1.0{{Date table sorting|May 1995}}

| {{No}}

{{No}}{{No}}

| {{Yes}}

{{No}}{{No}}

| {{No}}

| {{No}}

{{No}}

| OS/2 (i80386)

0.8.4{{Date table sorting|11 May 1993}}

| {{Yes}}

{{No}}{{No}}

| {{Yes}}

{{No}}{{No}}

| {{No}}

| {{No}}

{{No}}

| Experimental T800 transputer release

0.8.3{{Date table sorting|26 February 1993}}

| {{No}}

{{No}}{{No}}

| {{Yes}}

{{No}}{{No}}

| {{No}}

| {{No}}

{{No}}

|

0.8.1{{Date table sorting|19 October 1992}}

| {{No}}

{{No}}{{No}}

| {{Yes}}

{{No}}{{No}}

| {{No}}

| {{No}}

{{No}}

|

0.8{{Date table sorting|13 July 1992}}

| {{No}}

{{No}}{{No}}

| {{Yes}}

{{No}}{{No}}

| {{No}}

| {{No}}

{{No}}

| OS/2 (i80386); SunOS 3–4 (SPARC)

0.7{{Date table sorting|May 1991}}

| {{No}}

{{No}}{{No}}

| {{Yes}}

{{No}}{{No}}

| {{No}}

| {{No}}

{{No}}

| SunOS 3–4 (SPARC)

Comparison to Haskell

The syntax of Clean is very similar to that of Haskell, with some notable differences. In general, Haskell has introduced more syntactic sugar than Clean:

class="wikitable" border="1"
Haskell

! Clean

! Remarks

[ x | x <- [1..10] , isOdd x]

| [ x \\ x <- [1..10] | isOdd x]

| list comprehension

x:xs

| [x:xs]

| cons operator

data Tree a

= Empty

| Node (Tree a) a (Tree a)

|

:: Tree a

= Empty

| Node (Tree a) a (Tree a)

| algebraic data type

(Eq a, Eq b) => ...

| ... | Eq a & Eq b

| class assertions and contexts

fun t@(Node l x r) = ...

| fun t=:(Node l x r) = ...

| as-patterns

if x > 10 then 10 else x

| if (x > 10) 10 x

| if

References

{{Reflist}}

External links

  • [http://wiki.clean.cs.ru.nl/ Clean Wiki]
  • [https://clean-lang.org clean-lang.org]: public registry with Clean packages
  • [https://cloogle.org cloogle.org]: a search engine to search in Clean packages

{{Programming languages}}

Category:Functional languages

Category:Term-rewriting programming languages

Category:Free and open source compilers

Category:Cross-platform free software

Category:Programming languages created in 1987

Category:Statically typed programming languages