[m-dev.] for review: automatic header file inclusion guards.

[Fergus Henderson]

On 24-Jan-2001, Tyson Dowd <trd at cs.mu.OZ.AU> wrote:
> Implement automatic header file multiple inclusion guards.
> 
> Note that this should not affect the LLDS backend because it doesn't
> use header files to implement foreign_decls, so there is no chance of
> multiple inclusions.
> 
> compiler/intermod.m:
> 	Output 
> 		:- pragma source_file("...").
> 		#linenum
> 	before :- pragma foreign_decl(...).
> 
> 	This gives us the original context for foreign_decls, which is
> 	unique.

That fails if there is more than one `:- pragma foreign_decl'
on the same line.

Also that has the problem that Simon Taylor mentioned -- his memory is
clearly better than mine! -- about this forcing unnecessary compilation,
due to the `.opt' files changing if you add stuff (e.g. comments)
which changes the line numbers.

So I don't think this change is a good idea.

> +++ compiler/mercury_to_mercury.m	2001/01/23 21:42:47
> @@ -227,6 +227,10 @@
>  	io__state).
>  :- mode mercury_output_instance_methods(in, di, uo) is det.
>  
> +	% Output the given context 
> +:- pred mercury_output_prog_context(prog_context, io__state, io__state).
> +:- mode mercury_output_prog_context(in, di, uo) is det.

The comment here should explain that it outputs a
`:- pragma source_file' and `#<LINE>' directive.

> -mlds_output_c_hdr_decl(_Indent, foreign_decl_code(Lang, Code, Context)) -->
> +mlds_output_c_hdr_decl(Indent, foreign_decl_code(Lang, Code, Context)) -->
>  		% only output C code in the C header file.
>  	( { Lang = c } ->
> +		{ Context = context(File, Line) },

I'd suggest s/context/term__context/

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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