Editing Clean (programming language) (section)

==Compiling==
Compilation of Clean to [[machine code]] is performed as follows:

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

Earlier versions of the Clean compiler were written completely in [[C (programming language)|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 programming|imperative]] abstract [[graph rewriting]] machine.<ref>{{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}}</ref> 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 <code>Start</code> 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 browser]]s.
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.<ref>{{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}}</ref><ref>{{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 }}</ref>