Testing the failure cases of code is often as important as testing the successful paths. The Pandoc filter we worked on in the previous episode returns its result, and throws exceptions with formatted strings, in the IO type. This makes testing the failure cases much harder. In this episode we will introduce a function exposing …
Testing Failure with Either Instead of Exception Read More »
Recently, before implementing a new feature in pandoc-include-code, a Pandoc filter I have written, I needed to make some changes to the code. The program allowed what should’ve been considered conflicting modes of operation. In this episode I’ll perform the same modification, to show you how the right data structure can guide and improve your …
Refactoring and Finding the Right Data Structure Read More »
Some viewers have asked me about validation in Haskell. There are multiple kinds of validation; checking that values have a certain structure, which is deterministic, and things like querying a database to see if a user name is already taken, which is effectful and indeterministic. Today, I’ll focus on simple deterministic validation using smart constructors. …
In the final part of the “Domain Modelling with Haskell” series we factor out recursion from the Project data type, and use Fixplate to traverse the tree and accumulate reports. Although a highly flexible and powerful technique, it should not be employed prematurely due to its more advanced nature. Show Notes Welcome to Haskell at …
Domain Modelling with Haskell: Factoring Out Recursion Read More »
This is the third episode in the short series on Domain Modelling with Haskell. Now our hypothetical customer requires reporting not only at the level of individual projects, but also on the project group level. Our previous solution using Traversable and Foldable won’t help us much, so we use explicit recursion and the WriterT monad …
Domain Modelling with Haskell: Accumulating with WriterT Read More »
This is the second episode in the short series on Domain Modelling with Haskell. In this episode, we will generalize our domain model from the last episode, providing more fine-grained reporting, with less code. Show Notes In the last episode we modelled a basic project management system using Haskell data structures. We had the ability …
Domain Modelling with Haskell: Generalizing with Foldable and Traversable Read More »
Haskell is an amazing language for domain modelling, with its expressive data types and highly reusable abstractions. In this episode we will design the core of a simple project management system, laying the groundwork for later episodes in this small series. Show Notes We will model a basic project management system. This episode lays the …
Test suites with many example-based tests can contain a lot of repetition. While it’s possible to factor out much of the repetition using regular Haskell code, it can be useful to construct test cases from external files, which can be generated from other sources, or constructed by people not doing Haskell programming. In this video …
Dynamic Test Suites in Haskell using Hspec and Tasty Read More »
