[m-dev.] cvs diff: Bug fix for layoutst

[Tyson Richard DOWD]

> 
> Tyson Richard DOWD, you wrote:
> > 
> > However, when I finish the code for `type_of' ...
> 
> What does `type_of' do?
> 
> I have been using the name `type_of' for the following function:
> 
> 	:- type (type).
> 		% `type' is another name for `type_info(T)'.
> 		% ... some low-level magic to implement unification (etc.)
> 		% of values of type `type' omitted ...
> 
> 		% type_of(X) = T iff T is the type of X.
> 	:- func type_of(T::unused) = ((type)::out) is det.
> 	:- pragma c_code(type_of(_X::unused) = (Type::out),
> 			will_not_call_mercury, "Type = TypeInfo_for_T;").

Then you've changed your names slightly from when you asked for this to
be implemented - you used type_info, not type. Otherwise it is much
the same.

:- type type_info == c_pointer.

:- func type_of(T) = type_info.
:- mode type_of(unused) = out is det.

The c_code basically does what you ask, but will also need to check for
`univ' and give an error or something, (you can't do anything with a
univ without some data), and you should also look past any
equivalences at this point, for efficiency.

-- 
       Tyson Dowd           # "Well, let's just say, 'if your VCR is
                            #  still blinking 12:00, you don't
     trd at cs.mu.oz.au        #  want Linux'". 
http://www.cs.mu.oz.au/~trd #  --Bruce Perens, Debian's Fearless Leader