[Haskell-cafe] Re: Manual constructor specialization

Johan Tibell wrote:

On 10/9/07, David Benbennick wrote:

...

On 10/9/07, Johan Tibell wrote:

...

data Rope = Empty | Leaf | Node !Rope !Rope The point is that Empty can only appear at the top by construction How about indicating this in your data type? I.e.,

data Rope = Empty | NonEmptyRope data NonEmptyRope = Leaf | Node !NonEmptyRope !NonEmptyRope

That would be an idea. What are the performance effects of this? I'm trying to not have too many layers of indirection (I will spend quite some time reading -ddumpsimpl to optimize this library so anything that makes that simpler is a Good Thing.)

What you might want as a wrapper is a strict version of a maybe type:

data Rope = NoRope | JustRope {-# UNPACK #-} !ARope data ARope = Leaf {- rest of data here -} | Node {-# UNPACK #-} !NonEmptyRope {-# UNPACK #-} !NonEmptyRope

With the "constructor tagging" in the latest GHC the runtime indirection costs for such 2-constructor types should be quite low. -- Chris Kuklewicz