[m-dev.] generic result types

[Peter Ross]

On Wed, Feb 18, 2009 at 3:11 PM, Julien Fischer
<juliensf at csse.unimelb.edu.au> wrote:
>
> On Wed, 18 Feb 2009, Peter Ross wrote:
>
>> On Wed, Feb 18, 2009 at 2:44 PM, Julien Fischer
>> <juliensf at csse.unimelb.edu.au> wrote:
>>>
>>> On Wed, 18 Feb 2009, Peter Ross wrote:
>>>
>>>> Hi,
>>>>
>>>> Do people think it would be useful to add the following generic types
>>>> to the standard library?
>>>>
>>>> :- type result(T, E)
>>>>  --->    ok(T)
>>>>  ;       error(E)
>>>>  .
>>>>
>>>> :- type partial_result(T, E) == partial_result(T, T, E).
>>>>
>>>> :- type partial_result(T, P, E)
>>>>  --->    ok(T)
>>>>  ;       error(P, E)
>>>>
>>>> :- type result(E)
>>>>  --->    ok
>>>>  ;       error(E)
>>>>  .
>>>
>>> result/2 and result/1 almost already exist in the form of the
>>> maybe_error/[01] types.  Making them polymoprhic in the error type would
>>> give you the above.  Maybe, maybe_partial_result/3 could be added to the
>>> maybe module?
>>>
>> Good find, you are right they are essentially the same types.
>
> So, I propose that we make them the same types by making them
> polymorphic in the error type and the redefining the existing ones
> as equivlance types, for example:
>
>        :- type maybe_error(T) == maybe_error(T, string).
>
> and the same for the relevant ones in the I/O and stream modules.
> (This shouldn't break backwards compatability in such a huge way since
> most non-trivial Mercury modules already import the maybe module
> anyway.)
>
I agree with this proposal

>> I prefer the name result though, mainly because this is the name io
>> uses and so it seems more "natural" to me.
>
> Also maybe_partial_error doesn't make a great deal of sense!
>
True as well.
--------------------------------------------------------------------------
mercury-developers mailing list
Post messages to:       mercury-developers at csse.unimelb.edu.au
Administrative Queries: owner-mercury-developers at csse.unimelb.edu.au
Subscriptions:          mercury-developers-request at csse.unimelb.edu.au
--------------------------------------------------------------------------