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Haskell programmers spend a lot of time talking about type safety. The Haskell school of program construction advocates “capturing invariants in the type system” and “making illegal states unrepresentable,” both of which sound like compelling goals, but are rather vague on the techniques used to achieve them. Almost exactly one year ago, I published Parse, Don’t Validate as an initial stab towards

Just what exactly is a type? A common perspective is that types are restrictions. Static types restrict the set of values a variable may contain, capturing some subset of the space of “all possible values.” Under this worldview, a typechecker is sort of like an oracle, predicting which values will end up where when the program runs and making sure they satisfy the constraints the programmer wrote

Historically, I’ve struggled to find a concise, simple way to explain what it means to practice type-driven design. Too often, when someone asks me “How did you come up with this approach?” I find I can’t give them a satisfying answer. I know it didn’t just come to me in a vision—I have an iterative design process that doesn’t require plucking the “right” approach out of thin air—yet I haven’t bee

Currently, npm is the package manager for the frontend world. Sure, there are alternatives, but for the time being, npm seems to have won. Even tools like Bower are being pushed to the wayside in favor of the One True Package Manager, but what’s most interesting to me is npm’s relatively novel approach to dependency management. Unfortunately, in my experience, it is actually not particularly well

For me, this month marks the end of an era in my life: as of February 2018, I am no longer employed writing Haskell. It’s been a fascinating two years, and while I am excitedly looking forward to what I’ll be doing next, it’s likely I will continue to write Haskell in my spare time. I’ll probably even write it again professionally in the future. In the meantime, in the interest of both sharing wit

Nearly eight months ago, I wrote a blog post about unit testing effectful Haskell code using a library called test-fixture. That library has served us well, but it wasn’t as easy to use as I would have liked, and it worked better with certain patterns than others. Since then, I’ve learned more about Haskell and more about testing, and I’m pleased to announce that I am releasing an entirely new tes

Almost five months ago, I wrote a blog post about my new programming language, Hackett, a fanciful sketch of a programming language from a far-off land with Haskell’s type system and Racket’s macros. At that point in time, I had a little prototype that barely worked, that I barely understood, and was a little bit of a technical dead-end. People saw the post, they got excited, but development sort

Perhaps the most important abstraction a Haskell programmer must understand to effectively write modern Haskell code, beyond the level of the monad, is the monad transformer, a way to compose monads together in a limited fashion. One frustrating downside to monad transformers is a proliferation of lifts, which explicitly indicate which monad in a transformer “stack” a particular computation should

At the end of January of this year, I switched to a new job, almost exclusively because I was enticed by the idea of being able to write Haskell. The concept of using such an interesting programming language every day instead of what I’d been doing before (mostly Rails and JavaScript) was very exciting, and I’m pleased to say that the switch seems to have been well worth it. Haskell was a language

This documents my foray into Haskell programming. My functional programming language of choice is, for the moment, Racket (specifically Typed Racket), and while I’ve always been interested in Haskell, I’ve never taken the time to learn it properly. This is heavily inspired by Learning Racket, a fun series which is, in pretty much all respects, the direct reversal of this. I’m not sure how long I’l

This documents my foray into Haskell programming. My functional programming language of choice is, for the moment, Racket (specifically Typed Racket), and while I’ve always been interested in Haskell, I’ve never taken the time to learn it properly. This is heavily inspired by Learning Racket, a fun series which is, in pretty much all respects, the direct reversal of this. I’m not sure how long I’l