Skip to content

Blog

Foldr and Foldl in Haskell

This blog introduces how foldr and foldl work for a better usage them. Understanding the accumulation and association support from them is crucial.

foldr: Right-associative fold of a structure, lazy in the accumulator.

foldl: Left-associative fold of a structure, lazy in the accumulator.

In short, it helps you to construct a left/right associative structure. One of the real cases is you want to construct a left associative structure inside a parser , but you parse it in a right recursive way.

Note that this is a simple note, which has been already covered by documentation, and I wrote it because at the beginning I misunderstand its feature, so I wrote some code to try.

YAML Time Duration Support in Go

Last time, when one of users asked me "could I set up a 100d in his yaml file for Go time.Duration", my first action is why he cannot search the documentation by himself. But then, another problem overwhelmed my mind because actually I'm not sure about it. I don't know it as well.

After seeing the source code, I got the answer. However, the important inspiration here is: "how to make knowledge cohesive", hence the blog comes. In short, you should understand several concepts here:

  • whether the time duration is a standard specification?
  • does Go implementation allow to parse a string into different type?
  • how could it parse?

By enquiring these questions progressively, you can easily recognize how yaml works in a cohesive way instead of remembering some scattered knowledge about it.

Go: log.Fatalf is Bad for Framework Maintainers

In the open source framework, as long as maintainers can ensure the issues are caused by users instead of the framework, usually they could provide some suggestive guides and prevent themselves from delving into users code.

However, as a company scope framework maintainer, things differ greatly. As you claimed your framework helps them to write better code based on the company platforms, they're likely to rely on the maintainers to figure out some weird issues once it's related with the framework.

This blog records how I help to trouble shoot the weird issue of keeping restarting and failed to deploying caused by the log.Fatalf for our framework users, and my opinion why the log.Fatalf is bad.

Why Traversable Requires Applicative at Least

At the beginning, the blog name is why traversable requires applicative. However, later I feel like it is nonsense and just repeating the sentence to describe the traversable. It requires applicative of course because it uses that. As a result, I changed blog name because in this blog, we will learn about how the traversable uses applicative and why it requires applicative at least.

You should be familiar with Foldable before reading this blog, and I recommend you to read my previous blog why foldable requires monoid at least

In short, applicative is needed as we need to lift the chosen operator, pure the default value and keep applying by Foldable function foldr.