[m-dev.] for review: type_info/X switcheroo.

[Fergus Henderson]

On 02-Aug-1998, Tyson Dowd <trd at cs.mu.OZ.AU> wrote:
> Estimated hours taken: 3
> 
> Allow private_builtin:type_info/1 to be printed using io__write.
> 
> library/io.m:
> 	Use another horrible hack to find private_builtin:type_info/1
> 	to be detected and handled as if it were std_util:type_info/0
> 	for printing.
> 
> library/private_builtin.m:
> 	Add a hand-written type defintion for
> 	private_builtin:type_info/1.  (Much the same definition that
> 	was previously used for std_util:type_info/0.
> 
> library/std_util.m:
> 	Define std_util:type_info/0 as an abstract equivalence to
> 	private_builtin:type_info/1.
> 	Remove the old type defintions for std_util:type_info/0.

I'd like to see a test case.

> Index: library/io.m
> ===================================================================
> RCS file: /home/staff/zs/imp/mercury/library/io.m,v
> retrieving revision 1.159
> diff -u -r1.159 io.m
> --- io.m	1998/07/22 07:41:32	1.159
> +++ io.m	1998/07/31 00:37:33
> @@ -1708,6 +1708,12 @@
>  		io__write_univ_as_univ(OrigUniv)
>  	; { univ_to_type(Univ, C_Pointer) } ->
>  		io__write_c_pointer(C_Pointer)
> +	; { type_ctor_name(type_ctor(univ_type(Univ))) = "type_info" },
> +	  { type_ctor_module_name(type_ctor(univ_type(Univ))) =
> +			"private_builtin" } ->
> +	  	% XXX Horrible hack!
> +		{ TypeInfo = unsafe_cast(univ_value_as_type_any(Univ)) },
> +		io__write_string(type_name(TypeInfo))

It would be better if the comment explained why that hack was
necessary, rather than just exclaiming about how horrible it is.

> +	% XXX These two functions and the type definition 
> +	% are just temporary, they are used for the
> +	% horrible hack above.

If they are temporary, what is the planned replacement?

> +/* Ensure that the initialization code for the above module gets run. */
> +/*
> +INIT sys_init_type_info_module
> +*/
> +extern ModuleFunc unify_univ_module;
> +void sys_init_type_info_module(void); /* suppress gcc -Wmissing-decl warning */
> +void sys_init_type_info_module(void) {
> +	extern ModuleFunc type_info_module;
> +	type_info_module();
> +}

Please don't use nested extern declarations.

Why is the declaration for `unify_univ_module' there?

> +	% We define type_info as the same as the private_builtin
> +	% defintion of type_info.  `unit' is just used as a placeholder.

s/defintion/definition/

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>  |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3        |     -- the last words of T. S. Garp.