[m-dev.] proposal: drop automatic initialisation of solver types

[Mark Brown]

On 26-Oct-2007, Julien Fischer <juliensf at csse.unimelb.edu.au> wrote:
>
> There has been an on-and-off discussion about removing support for 
> automatic
> initialisation for solver types.
>
> Automatic initialisation is problematic because:
>
> * it prevents solver types from being properly polymorphic, e.g.
>   you cannot have the type foo(bar) where:
>
> 	:- solver type foo(T).
> 	:- solver type bar.
>
> * the introduction of calls to the initialisation predicates complicates
>   mode analysis.  Also, the compiler doesn't do a very good job of
>   introducing them anyway: the introduction of the calls can change det
>   code into semidet code etc.
>
> * we don't use automatic intialisation in practice anyway.  The solver
>   types in G12 all require (or we recommend) using explicit
>   initialisation predicates.
>
> * mode error messages are often poor or misleading because of
>   interactions between automatic initialisation and impure code.

* Sometimes you don't want to provide =/2, but provide some other mechanism
  for constraining variables to be equal.  In this case, it would be very
  useful for the compiler to detect implicit attempts to use =/2, and report
  them as a mode error.

>
> In light of this, I propose that we drop support for automatic
> initialisation.
>
> Objections?

Not at all.

Cheers,
Mark.

--------------------------------------------------------------------------
mercury-developers mailing list
Post messages to:       mercury-developers at csse.unimelb.edu.au
Administrative Queries: owner-mercury-developers at csse.unimelb.edu.au
Subscriptions:          mercury-developers-request at csse.unimelb.edu.au
--------------------------------------------------------------------------