Source-to-source compiler
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A source-to-source compiler, transcompiler or transpiler is a type of compiler that takes the source code of a program written in one programming language as its input and produces the equivalent source code in another programming language. A source-to-source compiler translates between programming languages that operate at approximately the same level of abstraction, while a traditional compiler translates from a higher level programming language to a lower level programming language. For example, a source-to-source compiler may perform a translation of a program from Pascal to C. An automatic parallelizing compiler will frequently take in a high level language program as an input and then transform the code and annotate it with parallel code annotations (e.g., OpenMP) or language constructs (e.g. Fortran's forall statements).[1]
Another purpose of source-to-source-compiling is translating legacy code to use the next version of the underlying programming language or an API that breaks backward compatibility. It will perform automatic code refactoring which is useful when the programs to refactor are outside the control of the original implementer (for example, converting programs from Python 2 to Python 3, or converting programs from an old API to the new API) or when the size of the program makes it impractical or time consuming to refactor it by hand.
Transcompilers may either keep translated code as close to the source code as possible to ease development and debugging of the original source code, or else they may change the structure of the original code so much, that the translated code does not look like the source code.[2] There are also debugging utilities that map the transpiled source code back to the original code; for example, JavaScript source maps allow mapping of the JavaScript code executed by a web browser back to the original source in a transpiled-to-JavaScript language.[3]
Contents
History
One of the earliest programs of this kind was Digital Research's XLT86 in 1981, a program written by Gary Kildall, which translated .ASM source code for the Intel 8080 processor into .A86 source code for the Intel 8086. Using global data flow analysis on 8080 register usage, the translator would also optimize the output for code size and take care of calling conventions, so that CP/M-80 and MP/M-80 programs could be ported to the CP/M-86 and MP/M-86 platforms automatically. XLT86 itself was written in PL/I-80 and was available for CP/M-80 platforms as well as for DEC VMS (for VAX 11/750 or 11/780).[4]
A similar, but much less sophisticated program was TRANS.COM, written by Tim Paterson in 1980 as part of 86-DOS. It could translate some Z80 assembly source code into .ASM source code for the 8086, but supported only a subset of opcodes, registers and modes, often still requiring significant manual correction and rework afterwards. Also it did not carry out any register and jump optimizations.[5][6]
Programming language implementations
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The first implementations of some programming languages started as transcompilers, and the default implementation for some of those languages are still transcompilers. In addition to the table below, a CoffeeScript maintainer provides a list of languages that compile to JavaScript.[7]
| Source language | Target language | Comment |
|---|---|---|
| C++ (originally known as "C with classes") |
C | The cfront transcompiler was doing the conversion |
| BCX | C | |
| Eiffel | C | |
| Lisaac | C | |
| Vala | C, with additional libraries such as GObject | |
| Julia | C | Julia generates native code and works well without C (or with), but a modified implementation of the Julia's implementation can compile individual functions or whole programs to C.[8][9] |
| CoffeeScript | JavaScript | |
| ClojureScript | JavaScript | |
| TypeScript | JavaScript | |
| ECMAScript 6 | JavaScript | Transcompiled using 6to5[10] or traceur-compiler[11] |
| Nim | C, C++, Objective-C, JavaScript | |
| Haxe | JavaScript, PHP, C++, C#, Python, and Java. Also compiling to bytecode such as ActionScript bytecode |
|
| C# | JavaScript | Transcompiled using ScriptSharp[12] |
| Dart | JavaScript | |
| Delphi Web Script / Object Pascal | JavaScript | Transcompiled using Smart Mobile Studio[13] |
| Mirah | Java | |
| Xtend[14] | Java | |
| PHP | C++ | Transcompiled using HipHop for PHP |
| Sass[15] | CSS | |
| LESS | CSS | |
| Java | Objective-C | Transcompiled using J2ObjC[16] |
| Ratfor | Fortran | |
| X10 | C++ and Java | |
| Chapel | C | |
| BASIC | C | Transcompiled using BaCon[17] |
| COBOL | C | Transcompiled using OpenCOBOL |
| COBOL | Java | Transcompiled using P3COBOL |
| OCaml bytecode | JavaScript | Transcompiled using js_of_ocaml from the Ocsigen project |
| Python | C++ | Transcompiled using ShedSkin[18] |
| Groovy | JavaScript | grooscript |
| Java | JavaScript | grooscript |
| Python | JavaScript | Brython |
| Ruby | JavaScript | Opal |
| Scheme | C | Stalin compiler |
| Java | C | java2c-transcompiler[19] |
Porting a codebase
When developers want to switch to a different language while retaining most of an existing codebase, it might be better to use a transcompiler compared to rewriting the whole software by hand. In this case, the code often needs manual correction because the automated translation might not work in all cases.
| Tool | Source language | Target language | Comments |
|---|---|---|---|
| 2to3 script | Python 2 | Python 3 | Even though 2to3 does its best at automating the translation process, further manual corrections are often needed. |
| Emscripten | LLVM bytecode | ECMAScript | This allows running C/C++ codebases in a browser for example |
| Google Web Toolkit | Java program that uses a specific API | JavaScript | The Java code is a little bit constrained compared to normal Java code. |
| Js_of_ocaml[20] of Ocsigen | OCaml | JavaScript | | |
| J2Eif[21] | Java | Eiffel | The resulting Eiffel code has classes and structures similar to the Java program but following Eiffel syntax and conventions. |
| C2Eif[22] | C | Eiffel | The resulting Eiffel code has classes and structures that try to be as clean as possible. The tool is complete and relies on embedding the C and assembly code if it cannot translate it properly. |
Examples
See also
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- Language interoperability
- Binary recompiler
- Code generation (compiler)
- Program transformation
- ROSE compiler framework – a source-to-source compiler framework
- Compiler-compiler
- Translation (computing)
- Language binding
- Language-independent specification
- Monkey (programming language)
- Intermediate language
References
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Digital Research (1981): XLT86 - 8080 to 8086 Assembly Language Translator - User's Guide. Digital Research Inc, Pacific Grove ([1]).
- ↑ Seattle Computer Products (1980): 86-DOS - Disk Operating System for the 8086. User's manual, version 0.3 - Preliminary. Seattle Computer Products, Seattle ([2]).
- ↑ Lua error in package.lua at line 80: module 'strict' not found. (NB. While the publishers claim this would be MS-DOS 1.1 and 2.0, it actually is SCP MS-DOS 1.25 and TeleVideo PC DOS 2.11.)
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
