Re: [Haskell-cafe] Manual constructor specialization

On Tue, 2007-10-09 at 17:40 +0200, Johan Tibell wrote:

On 10/9/07, David Benbennick wrote:

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On 10/9/07, Johan Tibell wrote:

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

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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.)

Another approach would be to define your invariant as a QuickCheck property. If you run your test suite often enough you will still find errors quickly. W.r.t. performance, note that allocating data on the C-stack might be slow, so make sure you also measure this. / Thomas