[Haskell-cafe] Haskell and the Software design process

[Gregory Crosswhite]

On May 9, 2010, at 1:04 AM, wren ng thornton wrote:

> If you're structuring your code with that invariant, then why aren't you using the correct type?

I do try to use the type system as much as possible to enforce constraints.  However. it is not always so simple as making sure that a list always has two elements;  you might be working with some kind of complicated data structure such that if you see that it satisfies some property then if you preserved the invariant correctly then you know that a given list must have at least two elements.

> If your response is that you use too many of the standard list functions, then write a module with ALT versions (because evidently you need one)


While, again, I do agree that it is smart to use the type system as much as possible to enforce constraints in order to avoid refutable pattern matches, I would argue that when you start creating duplicates of entire pre-existing modules towards this end then the cure may be starting to become worse that the disease.

Cheers,
Greg