[mercury-users] Maths and contexts.

[Michael Richter]

On 20 April 2012 23:33, Julien Fischer <juliensf at csse.unimelb.edu.au> wrote:

>   :- module test.
>   :- interface.
>   :- import_module io.
>   :- pred main(io::di, io::uo) is det.
>   :- implementation.
>   :- import_module decimal2.
>   :- import_module bool, integer.
>
>   main(!IO) :-
>      Context1 = make_context(integer(30), round_floor, signal(no, no)),
>      Context2 = make_context(integer(40), round_up, signal(no, no)),
>      X = to_number(Context1, "1000000"),
>      Y = to_number(Context2, "2900000"),
>      Z = X `add` Y,
>      io.write_string(to_scientific_**string(Z), !IO),
>      io.nl(!IO).
>
> Attempting to compile the above will result in the following compilation
> error:
>
>   Making Mercury/cs/test.c
>   test.m:013: In clause for predicate `main'/2:
>   test.m:013:   in unification of variable `Z'
>   test.m:013:   and term `add(X, Y)':
>   test.m:013:   type error in argument(s) of functor `add/2'.
>   test.m:013:   Argument 1 (X) has type `(some [C] decimal2.decimal(C))',
>   test.m:013:   expected type was `decimal2.decimal(C)';
>   test.m:013:   argument 2 (Y) has type `(some [C] decimal2.decimal(C))',
>   test.m:013:   expected type was `decimal2.decimal(C)'.
>   ** Error making `Mercury/cs/test.c'.
>

OK, thanks, Julien.  That's looking like a very promising line of inquiry.
 Adding the context to the creation of a number was the line I was going to
originally investigate but I was concerned at the need for run-time
checking.  Your solution eliminates that problem for me.

-- 
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of entering China our focus has really been what's best for the Chinese
people. It's not been about our revenue or profit or whatnot."
--Sergey Brin, demonstrating the emptiness of the "don't be evil" mantra.
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