Paul Chiusano

Functional programming, UX, tech, econ


Consulting services

I offer Scala and FP consulting services. If you're interested in working together, please contact me.

About my book

My book, Functional Programming in Scala, uses Scala as a vehicle for teaching FP. Read what people are saying about it.

Popular links

What is FP? (book intro)
The future of software
Type systems and UX: an example
CSS is unnecessary

When is it NOT preferable to specify your types first?

Very often when functional programming we specify the types first. Then once that’s done, we implement the term. Writing some tricky code? First, write out the type! By announcing (some) aspect of our intent to the compiler, we get an “accountability partner” that will verify we’ve remained true to our declared intent. That’s one part of it. But as Conor McBride likes to emphasize, types aren’t just about policing errors or checking:


How Twitter could easily address its rampant abuse problem

Twitter has a problem with abuse. Everyone knows this. I’ll explain the core issue, and then explain one way to fix it.


Unison now open source and has its own site

I finally wrapped up most of the housecleaning I wanted to do before releasing the code. It’s now public on GitHub and there’s also a dedicated project site and blog at and Twitter account. Going forward, I’ll be posting about Unison from, and any contributors to the project will also be able to use that space for Unison-related posts.


Unison update 7: structured refactoring sessions

As I mentioned in update 6, I’ve been spending the last few weeks doing some much-needed refactoring. Here’s an update on the progress:


Unison update 6: refactoring, technical debt, and motivation

No new screencasts to show this week. I’m in the middle of doing some much-needed refactoring. What happened? As of the last update, I had a decent expression editor. The missing final piece was adding a declaration layer to the editor, allowing a Unison panel to be edited much like a module in a regular programming language.