[m-dev.] How to add another grade (target language)

[Julien Fischer]

Hi,

On Mon, 15 Jun 2015, Charles Shuller wrote:

> Hello,
> 
> I'm interested in compiling mercury to JavaScript, as is already done for C and JavaScript.

Presumably, you meant "and Java" there?

> Can someone point me at some docs for the general compiler structure, and maybe some code that emits the C and Java grades??

The main document describing the compiler's structure is in
compiler/notes/compiler_design.html.

The code that emits C is in compiler/llds_out.m and its submodules
(low-level C backend) and compiler/mlds_to_c.m (high-level C backend).
The code that emits Java is in compiler/mlds_to_java.m and that for C#
in in compiler/mlds_to_csharp.m.  That said, those files are not the
best starting place IMO.  For example, the compiler's high-level C,
Java and C# backends are all variants of what is variously referred to
as the ml_backend or MLDS backend.  In its original form it is described
in the paper:

     Compiling Mercury to high-level C code
     Fergus Henderson and Zoltan Somogyi
     Proceedings of the 2002 International Conference on Compiler
     Construction Grenoble, France, April 2002.

Understanding the compilation scheme therein is the key to understanding
how those three backends above work.  Likewise, the design of the
low-level C backend is covered in:

     The execution algorithm of Mercury: an efficient purely declarative logic
     programming language
     Zoltan Somogyi, Fergus Henderson and Thomas Conway.
     Journal of Logic Programming, volume 29, number 1-3, October-December
     1996, pages 17-64.

(Both papers are available for download via tha papers page.)

For generating Javascript an alternative to adding a new backend may be
to use Emscripten to compile the C code generated by the Mercury
compiler.

Cheers,
Julien.