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

[Ralph Becket]

Julien Fischer, Friday, 26 October 2007:
> 
> 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.
> 
> In light of this, I propose that we drop support for automatic
> initialisation.
> 
> Objections?

I wholeheartedly endorse this change.
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