RE: [Caml-list] is there a more concise way to write this?

[David Allsopp <dra-news@metastack.com>]

Edgar Friendly wrote:
> On 01/20/2012 03:37 AM, David Allsopp wrote:
> > Actually, it's possible that with more cases it might be faster - it's
> > eliminating the allocation (at some point) of all the tuples needed
> > for the match case,
> 
> Doesn't the ocaml compiler not allocate the unnecessary tuples?
> https://ocaml.janestreet.com/?q=node/90
> 
> > it potentially eliminates a lot of linear comparisons to find the
> > correct match case (I don't think that the compiler would be able to
> > optimise that to a hash-based or index-based lookup)
> 
> Isn't the compiler's compilation strategy for match cases able to build an
> optimized tree of comparisons in cases like this?  I agree there's no easy
> index or hash strategy for this, but I'd expect it to turn this pattern
> matching into the equivalent of:
> 
> if a then if b then [a;b] else [a]
> else if b then [b] else []

Maybe for this case with two variables, yes - but it can't do that indefinitely: as the number of variables increases, the code size increases exponentially.


David