[clean-list] local functions as CAF

[Martin Wierich]

Hi Paul,

Paul de Mast wrote:
> Start = filter f [1..10]
> where
>         f x = x > y
>         where
>                 y =  2*3  // or a complex calculation
> 
> If we put y on the same level as f y is evaluated only once:
> 
> Start = filter f [1..10]
> where
>         f x = x > y
> 
>         y =  2*3  // or a complex calculation
> 
> Is it possible that the compiler optimises the first situation by lifting y
> to the same level as f?

In principle yes, of course. It would somehow be different from pure graph
rewriting semantics but I wouldn't care about that as long as the outcome of the
program stays the same. One had to take care with uniqueness: imagine y would
deliver a unique array...

cheers
  Martin Wierich