[m-dev.] switching on constant functions

[Ian MacLarty]

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.

Ian.
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