billboswell
Effective Haskell: Chapter 9 - Monad instance error (page 357)
Creating the instance of Monad Outlaw described in the text results in error:
• No instance for (Applicative Outlaw)
arising from the superclasses of an instance declaration
• In the instance declaration for ‘Monad Outlaw’
Resolved by adding Applicative instance:
Instance Applicative Outlaw where
pure = return
First Post!
RebeccaSkinner
Author of Effective Haskell
Good catch, thanks. I’ll add an errata item about this.
Popular Pragmatic Bookshelf topics
Following the steps described in Chapter 6 of the book, I’m stuck with running the migration as described on page 84:
bundle exec sequel...
New
On the page xv there is an instruction to run bin/setup from the main folder. I downloaded the source code today (12/03/21) and can’t see...
New
The generated iex result below should list products instead of product for the metadata. (page 67)
iex> product = %Product{}
%Pento....
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
The book has the same “Problem space/Solution space” diagram on page 18 as is on page 17. The correct Problem/Solution space diagrams ar...
New
Hi,
I am getting an error I cannot figure out on my test.
I have what I think is the exact code from the book, other than I changed “us...
New
Hi all,
currently I wonder how the Tailwind colours work (or don’t work).
For example, in app/views/layouts/application.html.erb I have...
New
Hi, I’ve got a question about the implementation of PubSub when using a Phoenix.Socket.Transport behaviour rather than channels.
Before ...
New
Book: Programming Phoenix LiveView, page 142 (157/378), file lib/pento_web/live/product_live/form_component.ex, in the function below:
d...
New
From page 13:
On Python 3.7, you can install the libraries with pip by running these commands inside a Python venv using Visual Studio ...
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
If it’s a mechanical keyboard, which switches do you have?
Would you recommend it? Why?
What will your next keyboard be?
Pics always w...
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
You might be thinking we should just ask who’s not using VSCode :joy: however there are some new additions in the space that might give V...
New
Build highly interactive applications without ever leaving Elixir, the way the experts do. Let LiveView take care of performance, scalabi...
New
This is going to be a long an frequently posted thread.
While talking to a friend of mine who has taken data structure and algorithm cou...
New
Was just curious to see if any were around, found this one:
I got 51/100:
Not sure if it was meant to buy I am sure at times the b...
New
Author Spotlight
Erin Dees
@undees
Welcome to our new author spotlight! We had the pleasure of chatting with Erin Dees, co-author of ...
New
A Brief Review of the Minisforum V3 AMD Tablet.
Update: I have created an awesome-minisforum-v3 GitHub repository to list information fo...
New
Node.js v22.14.0 has been released.
Link: Release 2025-02-11, Version 22.14.0 'Jod' (LTS), @aduh95 · nodejs/node · GitHub
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /ruby
- /wasm
- /erlang
- /phoenix
- /keyboards
- /rails
- /python
- /js
- /security
- /go
- /swift
- /vim
- /clojure
- /haskell
- /emacs
- /java
- /svelte
- /onivim
- /typescript
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /elm
- /flutter
- /vscode
- /ash
- /opensuse
- /html
- /centos
- /php
- /deepseek
- /zig
- /scala
- /lisp
- /textmate
- /sublime-text
- /react-native
- /nixos
- /debian
- /agda
- /kubuntu
- /arch-linux
- /django
- /revery
- /ubuntu
- /deno
- /manjaro
- /spring
- /nodejs
- /diversity
- /lua
- /julia
- /slackware
- /c
Devtalk Sponsors
Practical resources that improve the lives of professional developers.
We build trusted fault-tolerant systems that scale to billions of users.
Real-time error tracking, performance insights, and observability for devs.
Develop your skills with books, videos, and courses.
Catch errors, track performance, monitor hosts and more.
Enabling companies to succeed by building software people love.
Courses that move you from confusion to "Aha, now I get it!"