shaolang
Real-World Event Sourcing: `handle_command` for subtract doesn't make sense (pg 8)
The book implements handle_command/2 for :sub as follows:
def handle_command(%{value: val}, %{cmd: :sub, value: v}) do
%{event_type: :value_subtracted, max(@min_state_value, val - v)
end
The value in the created event is the result expected after subtraction, i.e., it is not the subtrahend. It can be reimplemented as follows instead:
def handle_command(%{value: val}, %{cmd: :sub, value: v) do
subtrahend = if(val >= v, do: v, else: val)
%{event_type: :value_subtracted, value: subtrahend}
end
First Post!
dmitrykleymenov
I’ve found the same issue, but think the code should be like:
def handle_command(%{value: val}, %{cmd: :sub, value: v}) do
%{event_type: :value_subtracted, value: min(val - @min_state_value, v)}
end
In this case we can use @min_state_value correctly(not only 0)
Popular Pragmatic Bookshelf topics
This test is broken right out of the box…
— FAIL: TestAgent (7.82s)
agent_test.go:77:
Error Trace: agent_test.go:77
agent_test.go:...
New
Title: Hands-on Rust: question about get_component (page 295)
(feel free to respond. “You dug you’re own hole… good luck”)
I have somet...
New
Hi Travis! Thank you for the cool book! :slight_smile:
I made a list of issues and thought I could post them chapter by chapter. I’m rev...
New
I am working on the “Your Turn” for chapter one and building out the restart button talked about on page 27. It recommends looking into ...
New
Title: Web Development with Clojure, Third Edition, vB17.0 (p9)
The create table guestbook syntax suggested doesn’t seem to be accepted ...
New
I’m new to Rust and am using this book to learn more as well as to feed my interest in game dev. I’ve just finished the flappy dragon exa...
New
The test is as follows:
Scenario: Intersecting a scaled sphere with a ray
Given r ← ray(point(0, 0, -5), vector(0, 0, 1))
And s ← sphere...
New
In general, the book isn’t yet updated for Phoenix version 1.6. On page 18 of the book, the authors indicate that an auto generated of ro...
New
When trying to run tox in parallel as explained on page 151, I got the following error:
tox: error: argument -p/–parallel: expected one...
New
@mfazio23
Android Studio will not accept anything I do when trying to use the Transformations class, as described on pp. 140-141. Googl...
New
Other popular topics
Reading something? Working on something? Planning something? Changing jobs even!?
If you’re up for sharing, please let us know what you’...
New
Free and open source software is the default choice for the technologies that run our world, and it’s built and maintained by people like...
New
I’m thinking of buying a monitor that I can rotate to use as a vertical monitor?
Also, I want to know if someone is using it for program...
New
Oh just spent so much time on this to discover now that RancherOS is in end of life but Rancher is refusing to mark the Github repo as su...
New
Learn different ways of writing concurrent code in Elixir and increase your application's performance, without sacrificing scalability or...
New
Continuing the discussion from Thinking about learning Crystal, let’s discuss - I was wondering which languages don’t GC - maybe we can c...
New
Author Spotlight
Rebecca Skinner
@RebeccaSkinner
Welcome to our latest author spotlight, where we sit down with Rebecca Skinner, auth...
New
Author Spotlight:
VM Brasseur
@vmbrasseur
We have a treat for you today! We turn the spotlight onto Open Source as we sit down with V...
New
Explore the power of Ash Framework by modeling and building the domain for a real-world web application.
Rebecca Le @sevenseacat and ...
New
This is a very quick guide, you just need to:
Download LM Studio: https://lmstudio.ai/
Click on search
Type DeepSeek, then select the o...
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /wasm
- /ruby
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /clojure
- /java
- /emacs
- /haskell
- /svelte
- /typescript
- /onivim
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /elm
- /flutter
- /vscode
- /ash
- /html
- /opensuse
- /deepseek
- /zig
- /centos
- /php
- /scala
- /react-native
- /lisp
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /django
- /deno
- /kubuntu
- /arch-linux
- /nodejs
- /spring
- /ubuntu
- /revery
- /manjaro
- /julia
- /lua
- /diversity
- /markdown
- /slackware









