[m-dev.] switching on constant functions

[Julien Fischer]

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.

Julien.
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