[m-rev.] diff: fix bugs in smart recompilation

[Fergus Henderson]

On 24-Jul-2001, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> 
> +:- func item_is_unchanged(item, item) = bool.
> +
> +	% We don't need to compare the varsets. What matters is that
> +	% the variable numbers in the arguments and body are the same,
> +	% the names are irrelevant.

Hmm, that looks wrong to me.  Maybe you're not aware of the following sentence
from the Mercury language reference manual:

 | The scope of type variables in a predicate or function's type
 | declaration extends over any explicit type qualifications in the
 | clauses for that predicate or function, so explicit type qualifications
 | can refer to those type variables.

So if, for example, you write

	:- module example.
	:- interface.
	:- import_module io.

	:- pred main(io__state::di, io__state::uo) is det.

	:- implementation.

	main --> foo(0, "").

	:- pred foo(T1, T2, io__state, io__state).
	:- mode foo(in, in, di, uo) is det.

	foo(_, _) -->
		io__read(R `with_type` io__read_result(T1)),
		io__print(R),
		io__nl.

and then you change the pred declaration for `foo' to

	:- pred foo(T2, T1, io__state, io__state).

then the resulting program will behave differently.


Could you please add this one as a test case?
I think the code for smart recompilation will also need to be
changed to make it work...

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  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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