Prevent optimization from tempering with unsafePerformIO

[Josef Svenningsson]

On 10/17/07, Bernd Brassel <bbr at informatik.uni-kiel.de> wrote:
> > why do you want to do this unsafely,
> > instead of just using 'length'?  unsafePerformIO is a very slow
> > function, remember)
>
> The big picture is that we generate programs like this example in order
> to compile the functional logic language Curry down to Haskell.
> Basically, there are two ways to do this:
>
> a) write an interpreter for Curry in Haskell, e.g., by employing
> non-determinism monads
> b) extend Haskell by employing side effects
>
> Alternative a) is not really an issue for us. Doing it this way, all
> Curry programs will suffer in performance in such a magnitude that - in
> comparison - unsafePerformIO is super-fast. In addition, we already have
> interpreters for Curry which I do not assume a Haskell interpreter to
> outperform without 5 years worth of tuning.
>
> Alternative b) is the choice, because doing it this way, all
> deterministic, i.e., purely functional parts of Curry programs would
> take advantage of Haskell being a functional language. If then the logic
> parts are not so fast, e.g., because unsafePerformIO is slow, this does
> not matter so much. In comparison to other approaches (like Alternative
> a) and many other implementations of Curry) our slogan is: "make
> functions fast and logic possible". Fast functions will outweigh the
> slowdown for logics. But to get "functions fast" employing optimization
> sounds like a good idea to me. But even without any optimization, our
> system can compare well to most other implementations for many
> applications.
>
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.

Just my 2 cents,

/Josef