molleweide

molleweide

Effective Haskell: ch 2 > destructuring lists

  1. The function I am testing is handleNums on page 68.

It returns this error message:

    λ: :reload
    [1 of 1] Compiling Main             ( Chapter2.hs, interpreted )

    Chapter2.hs:306:1: error:
        • Non type-variable argument
            in the constraint: Show ((a -> Bool) -> Bool)
          (Use FlexibleContexts to permit this)
        • When checking the inferred type
            handleNums :: forall a.
                          (Integral a, Show ((a -> Bool) -> Bool), Num ((a -> Bool) -> Bool),
                           Eq ((a -> Bool) -> Bool)) =>
                          [(a -> Bool) -> Bool] -> [Char]
        |
    306 | handleNums l =
        | ^^^^^^^^^^^^^^...
    Failed, no modules loaded.
  1. I sort of understand the err msg but I add this info here so you can see that this can happen to a reader.

  2. Did I post this information under the correct category. Is “errata” correct or should I have chose something else?

  3. The book is great! I’m chugging along and it feels really good.

First Post!

RebeccaSkinner

RebeccaSkinner

Author of Effective Haskell

Hi! Can you share the code that you are trying to load. I can’t reproduce this error from the example locally.

Where Next?

Popular Pragmatic Bookshelf topics Top

oaklandgit
Hi, I completed chapter 6 but am getting the following error when running: thread 'main' panicked at 'Failed to load texture: IoError(O...
New
dsmith42
Hey there, I’m enjoying this book and have learned a few things alredayd. However, in Chapter 4 I believe we are meant to see the “>...
New
taguniversalmachine
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
Henrai
Hi, I’m working on the Chapter 8 of the book. After I add add the point_offset, I’m still able to see acne: In the image above, I re...
New
redconfetti
Docker-Machine became part of the Docker Toolbox, which was deprecated in 2020, long after Docker Desktop supported Docker Engine nativel...
New
gorkaio
root_layout: {PentoWeb.LayoutView, :root}, This results in the following following error: no “root” html template defined for PentoWeb...
New
mcpierce
@mfazio23 I’ve applied the changes from Chapter 5 of the book and everything builds correctly and runs. But, when I try to start a game,...
New
SlowburnAZ
Getting an error when installing the dependencies at the start of this chapter: could not compile dependency :exla, "mix compile" failed...
New
dachristenson
I just bought this book to learn about Android development, and I’m already running into a major issue in Ch. 1, p. 20: “Update activity...
New
roadbike
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 Top

Devtalk
Reading something? Working on something? Planning something? Changing jobs even!? If you’re up for sharing, please let us know what you’...
1052 22283 402
New
PragmaticBookshelf
Take your Go skills to the next level by learning how to design, develop, and deploy a distributed service. Start from the bare essential...
New
AstonJ
Do the test and post your score :nerd_face: :keyboard: If possible, please add info such as the keyboard you’re using, the layout (Qw...
New
PragmaticBookshelf
Learn different ways of writing concurrent code in Elixir and increase your application's performance, without sacrificing scalability or...
New
PragmaticBookshelf
Build highly interactive applications without ever leaving Elixir, the way the experts do. Let LiveView take care of performance, scalabi...
New
DevotionGeo
The V Programming Language Simple language for building maintainable programs V is already mentioned couple of times in the forum, but I...
New
PragmaticBookshelf
Author Spotlight: Peter Ullrich @PJUllrich Data is at the core of every business, but it is useless if nobody can access and analyze ...
New
First poster: bot
zig/http.zig at 7cf2cbb33ef34c1d211135f56d30fe23b6cacd42 · ziglang/zig. General-purpose programming language and toolchain for maintaini...
New
PragmaticBookshelf
Get the comprehensive, insider information you need for Rails 8 with the new edition of this award-winning classic. Sam Ruby @rubys ...
New
xiji2646-netizen
Woke up to this today: Claude Code’s complete source code exposed via npm source map. Not a snippet. All 512,000 lines. 1,900 TypeScript ...
New

Sub Categories: