Fun with GHC's optimiser
Manuel M. T. Chakravarty
chak@cse.unsw.edu.au
Fri, 22 Dec 2000 17:13:07 +1100
Simon,
> But I think the way to handle
> it is this. Suppose we have
>
> f x y = ....(f ex (C a b))...
>
> where C is a constructor, and where y is scrutinised by a
> case expression somewhere in f's body. Then, in this recursive
> call to f, we know what y will be, and we could save the case in
> the recursive call. So make a specialised version of f, thus:
>
> fs x a b = let y = C a b in (...original body of f...)
>
> Now add a RULE to f, saying
>
> f x (C a b) ===> fs x a b
>
> This is very much the way type specialisation works. Now every
> call to f that has a (C a b) argument will benefit. Including
> the recursive call to f in fs's RHS, so fs will become the self-recursive
> tight loop you want, leaving f as a sort of 'impedence matcher' for
> callers elsewhere.
Sounds like a good idea to me :-)
Cheers,
Manuel