[m-dev.] generic result types

[Julien Fischer]

On Wed, 18 Feb 2009, Peter Ross wrote:

> On Wed, Feb 18, 2009 at 2:39 PM, Julien Fischer
> <juliensf at csse.unimelb.edu.au> wrote:
>>
>> On Wed, 18 Feb 2009, Peter Ross wrote:
>>
>>> On Wed, Feb 18, 2009 at 2:12 PM, Julien Fischer
>>> <juliensf at csse.unimelb.edu.au> wrote:
>>>>
>>>> On Wed, 18 Feb 2009, Peter Ross wrote:
>>>>
>>>>> On Wed, Feb 18, 2009 at 1:47 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)
>>>>>>>  .
>>>>>>>
>>>>>>> Then the various io and stream types could be redefined in terms of
>>>>>>> these
>>>>>>> types.
>>>>>>>
>>>>>>> I ask because we have written a lot of code at MC which should use
>>>>>>> these
>>>>>>> generic
>>>>>>> result types, so I was going to add this to our library but ian
>>>>>>> suggested we should
>>>>>>> see first if it goes better in the mercury standard library.
>>>>>>
>>>>>> In which module would they be defined?
>>>>>>
>>>>> I was thinking result.m, just like maybe.m and cohorts.
>>>>
>>>> Are you proposing that there be generic result types for all the types
>>>> duplicated in the io and stream modules?  The above doesn't cover the
>>>> case where they have an eof functor.
>>>>
>>> No only the types with two functors, ok and error.
>>
>> In which case the names you have chosen above clash with the 3-functor
>> versions in the io and stream modules.
>>
> I'm more interested in whether or not this is a sufficently useful
> module for standard library inclusion.

Yes, IMO - but see my post about the maybe_error types.  (We pretty
much already have it in the stdlib.)

Julien.
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