[m-dev.] switching on constant functions

[Ian MacLarty]

On Mon, Dec 22, 2008 at 03:14:13PM +1100, Julien Fischer wrote:
>
> On Mon, 22 Dec 2008, Ian MacLarty wrote:
>
>> On Mon, Dec 22, 2008 at 12:25:17PM +1100, Julien Fischer wrote:
>>>
>>> On Mon, 22 Dec 2008, Julien Fischer wrote:
>>>
>>>>
>>>> On Mon, 22 Dec 2008, Ian MacLarty wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> I'd like to be able to switch on the values of constant functions.
>>>>> For example suppose I have the functions:
>>>>>
>>>>>    :- func a = (string::(out(bound("a")))).
>>>>>    :- func b = (string::(out(bound("b")))).
>>>>>
>>>>> then I'd like to be able to write a switch like:
>>>>>
>>>>>    % X has inst bound("a" ; "b") before the switch.
>>>>>    (
>>>>>        X = a,
>>>>>        ...
>>>>>    ;
>>>>>        X = b,
>>>>>        ...
>>>>>    )
>>>>>
>>>>> Would there be any objections to extending the language to handle this?
>>>>> If not what would be the best way to implement it?  I was thinking of
>>>>> replacing constant functions, whose output is an inst with a single
>>>>> value, by that value before or in the switch detection pass.
>>>>
>>>> What if the type involved is abstract and imported from another module?
>>>
>>> Obviously the second follows from the first there ;-)
>>>
>>
>> That wouldn't be allowed.
>
> I think you need to make a stronger case for it than this.  (A better
> description of change, e.g. the proposed change to the reference manual,
> would help.)
>
> As it stands, I don't think this is a good idea since it complicates
> switch detection, its description of that in the reference manaual,
> and consequently makes it harder for users to understand.
>

Okay.
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