[mercury-users] Maths and contexts.

[Julien Fischer]

On Sat, 21 Apr 2012, Mark Brown wrote:

> On 20-Apr-2012, Michael Richter <ttmrichter at gmail.com> wrote:
>> 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.
>
> Julien said it gives you compile-time checking, not that it eliminates
> run-time checking.  You'll still need run-time checks if two contexts
> don't originate from the same call to make_context.

What runtime checks are you performing there?  That the two contexts
are in fact semantically identical?

Cheers,
Julien.
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