I recently gave a talk at BayHac about some of the things I've learned in building production Reflex applications. If you're interested, you can find it here:
video slides github
Recently there has been a lot of discussion and questions about the differences between the big three Haskell web frameworks: Happstack, Yesod, and Snap. Different pieces of the answer have been discussed in a number of places. In this post, I'd like to try to give a more complete comparison. Hopefully it will be relatively unbiased, but without being so watered down that it is useless. I've succeeded if you can't tell which framework I'm a major contributor to based solely on the text of this post. Happstack First, up is Happstack , the oldest of the three with original commit history as early as February, 2005. Happstack used to be called HAppS . It was primarily composed of a web server based on lazy IO, a fairly radical (for the time) in-memory persistence approach for storing and versioning native Haskell data types, and a library called IxSet for making it easier to use this state system with relational data access patterns. I've heard a number of pe...
I recently went through the process of setting up a private Nix binary cache. It was not obvious to me how to go about it at first, so I thought I would document what I did here. There are a few different ways of going about this that might be appropriate in one situation or another, but I’ll just describe the one I ended up using. I need to serve a cache for proprietary code, so I ended up using a cache served via SSH. Setting up the server For my cache server I’m using an Amazon EC2 instance with NixOS. It’s pretty easy to create these using the public NixOS 18.03 AMI. I ended up using a t2.medium with 1 TB of storage, but the jury is still out on the ideal tradeoff of specs and cost for our purposes. YMMV. The NixOS AMI puts the SSH credentials in the root user, so log in like this: ssh -i /path/to/your/key.pem root@nixcache.example.com To get your new NixOS machine working as an SSH binary cache there are two things you need to do: generate a signing key and turn on cache serv...
Awhile back I was discussing dependent types with someone and we ended up concluding that dependent types can always be replaced by a runtime Maybe. This seemed to me then (and still does today) as a fairly surprising and provocative conclusion. So I thought I'd put the idea out there and see what people think. Let's look at a few examples that are commonly used to illustrate dependent types: Vectors of length N Matrices of size m x n Sorted lists Height-balanced trees (trees where the height of subtrees differ by at most one) The argument is roughly as follows. All of these examples ultimately boil down to enforcing some kind of constraint on some data types. The more powerful your dependent type system, the more rich and expressive will be the constraints that you can enforce. If we take this thought experiment to its logical conclusion, we end up with a dependent type system that allows us to enforce any constraint that can be computed. The important rea...
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