Re: [Haskell-cafe] Haskell and the Software design process

brad.larsen:

On Sun, May 2, 2010 at 4:10 PM, Don Stewart wrote:

...

I don't believe anyone has written a "Programming Haskell in the Large" book (or any other similar functional language??), but there is lots of experience in this community working on big, long lived code bases.

Some key points: [...]    * picking a good data type (like a zipper) will make hundreds of          unit tests meaningless -- improving productivity.

Don,

What sort of tests were you thinking of that a zipper would render pointless? Could you elaborate?

Well, specifically, zippers statically ensure that you always have a valid index into a set. No need for arr ! 10 out of bounds checks, when the type guarantees that indexing can never be out of bounds. Clever types move invariants from dynamic properties to ones the compiler can prove, saving you effort. -- Don