Prevent optimization from tempering with unsafePerformIO

[Bernd Brassel]

> May I suggest a third route that has the advantages of both your
> approaches. The backside is of course that it takes a bit of work. My
> suggestion is to do an effect analysis of your curry programs to
> identify the purely functional parts and compile them directly to pure
> Haskell. The rest of the programs can run in a monad. This approach
> should be more robust than relying on unsafePerformIO. It is also very
> much in the spirit of your slogan.

Thank you for the suggestion. We were thinking along the lines of
identifying "the purely functional parts and compile them directly to
pure Haskell" as a possibility of optimization (with some code
duplication).  But if the "rest of the programs can run in a monad" the
question is: How much of the example program I submitted would you
classify as "purely functional"? Actually, most of it is purely
functional apart from the (?) - operator. But I do not see a way to make
use of this. If, however, the whole program is classified as
"non-functional" then this is definitely not in the spirit of the
slogan. One effect we like very much about our implementation is that
all expressions which do not depend on non-deterministic values are
shared across the whole search. Note, that this dependence is a dynamic
property. If the code of programs like the example was monadic, I do not
see how not to loose this property.

Thanks again!
Bernd