Types and Testing in Haskell

Daniel Patterson explores the relationship between static types and testing in Haskell, discussing where to strengthen types and where to write tests.

New York Haskell Users Group, November 13, 2014 Types and Testing in Haskell by Daniel Patterson How should you test code in Haskell? What do tests give that types don't, and vice versa? This talk will start with a quick introduction to techniques for testing in Haskell. After, we'll deal with the following questions: Where (and how) should we strengthen types? Where should we have more (or fewer) tests? And how should we be thinking about testing in a language with a type system as expressive as what Haskell has? Our goal is to end up with a more nuanced view of correctness than just "it type checked, so it's (probably) right", and to think about what it means to be (reasonably) sure that code is correct. Daniel Patterson has been writing web code in Haskell since late 2007, and more recently started Position Development, a software consultancy building web based applications primarily in Haskell. He's interested in whatever can make writing correct software easier, whether it be expressive static types (with Haskell being a great example), or figuring out how to make testing easier. As an example of the latter, he was central in developing syntactically convenient testing blocks in the education oriented language Pyret at Brown University.