molleweide
Effective Haskell: ch 2 > destructuring lists
- The function I am testing is
handleNumson 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.
-
I sort of understand the err msg but I add this info here so you can see that this can happen to a reader.
-
Did I post this information under the correct category. Is “errata” correct or should I have chose something else?
-
The book is great! I’m chugging along and it feels really good.
First Post!
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.
Popular Pragmatic Bookshelf topics
Many tasks_proj/tests directories exist in chapters 2, 3, 5 that have tests that use the custom markers smoke and get, which are not decl...
New
I can’t setup the Rails source code. This happens in a working directory containing multiple (postgres) Rails apps.
With:
ruby-3.0.0
s...
New
I’m under the impression that when the reader gets to page 136 (“View Data with the Database Inspector”), the code SHOULD be able to buil...
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
Hi, I’ve got a question about the implementation of PubSub when using a Phoenix.Socket.Transport behaviour rather than channels.
Before ...
New
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
@parrt
In the context of Chapter 4.3, the grammar Java.g4, meant to parse Java 6 compilation units, no longer passes ANTLR (currently 4....
New
Hello @herbert ! Trying to get the very first “Hello, Bracket Terminal!" example to run (p. 53). I develop on an Amazon EC2 instance runn...
New
Hello faithful readers! If you have tried to follow along in the book, you are asked to start up the dev environment via dx/build and ar...
New
Getting an error when installing the dependencies at the start of this chapter:
could not compile dependency :exla, "mix compile" failed...
New
Other popular topics
Stop developing web apps with yesterday’s tools. Today, developers are increasingly adopting Clojure as a web-development platform. See f...
New
Design and develop sophisticated 2D games that are as much fun to make as they are to play. From particle effects and pathfinding to soci...
New
We have a thread about the keyboards we have, but what about nice keyboards we come across that we want? If you have seen any that look n...
New
Just done a fresh install of macOS Big Sur and on installing Erlang I am getting:
asdf install erlang 23.1.2
Configure failed.
checking ...
New
Build highly interactive applications without ever leaving Elixir, the way the experts do. Let LiveView take care of performance, scalabi...
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
Dmitry Zinoviev
@aqsaqal
Today we’re putting our spotlight on Dmitry Zinoviev, author of Data Science Essentials in ...
New
Author Spotlight:
Bruce Tate
@redrapids
Programming languages always emerge out of need, and if that’s not always true, they’re defin...
New
If you’re getting errors like this:
psql: error: connection to server on socket “/tmp/.s.PGSQL.5432” failed: No such file or directory ...
New
Use advanced functional programming principles, practical Domain-Driven Design techniques, and production-ready Elixir code to build scal...
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
- /onivim
- /typescript
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /flutter
- /elm
- /vscode
- /ash
- /html
- /opensuse
- /zig
- /centos
- /deepseek
- /php
- /scala
- /react-native
- /lisp
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /django
- /deno
- /kubuntu
- /arch-linux
- /nodejs
- /ubuntu
- /revery
- /manjaro
- /spring
- /julia
- /lua
- /diversity
- /markdown
- /c









