[m-dev.] Adding Loops to Mercury

[Julien Fischer]

Hi,

On Fri, 3 Jan 2014, Peter Schachte wrote:

> As for the semantics, a generalisation of Mercury's 'all' construct
> that can generate output would fit well with Mercury.  Here's a paper
> I wrote a decade ago doing this for Prolog.  At the time, Fergus
> Henderson told me there was some shortcoming in Mercury's type or mode
> system that would make this difficult to do for Mercury, but I don't
> remember the specifics.

Here's the minutes from the meeting in which the proposal was discussed:

     <http://lists.mercurylang.org/pipermail/developers/2000-December/010812.html>

(There was, I think, a mail from Adrian Pellas-Rice describing the nature
of the brick wall he hit while trying to implement the above, but I
can't seem to find that.  I would guess that's the shortcoming that
Fergus mentioned.)

One other issue with sequence quantification is that in the absence of
constructor classes I think we are restricted to quantifying over lists
(or more generally, a predefined set of types) rather than sequences
in general (i.e. instances of some sequence type class).

Cheers,
Julien.