PragProg Customers

Effective Haskell - inaccurate description of filter example (page 61)

tusktenon

tusktenon

Effective Haskell - inaccurate description of filter example (page 61)

@RebeccaSkinner

On p.61 in Chapter 2, the following is described as finding “the sum of the first ten odd numbers”:

λ (foldr (+) 0 . filter odd) [0..10]
25

In fact, this code sums the odd numbers between 0 and 10 – that is, the first five odd numbers. For the sum of the first ten odd numbers, you’d probably want something like

λ (foldr (+) 0 . map (\x -> 2 * x + 1)) [0..9]
100
2 comments
#errata/book-effective-haskell
1 302 2

Most Liked

tusktenon

tusktenon

It’s actually not a bad example of the differing use cases for map and filter: if the problem is to “sum the odd numbers between m and n,” then filter is perfect; if the problem is to “sum the first n odd numbers,” map is more appropriate.

I’ve only made it to chapter 3 so far, but I’m really enjoying the book!

1
Post #3

Where Next?

View thread on forum
View Effective Haskell's book portal
Post errata for this book
Post a suggestion for this book
Post a question about this book
Post a review about this book
Home PragProg Customers
#errata/book-effective-haskell
1 302 2
Last post

Popular Pragmatic Bookshelf topics Top

jon
PragProg Customers

The Pragmatic Programmer, 20th Anniversary Edition errata
Some minor things in the paper edition that says “3 2020” on the title page verso, not mentioned in the book’s errata online: p. 186 But...
#errata/book-the-pragmatic-programmer-20th-anniversary-edition
10 2628 9
New
sdmoralesma
PragProg Customers

Web Development with Clojure, Third Edition: migrations/create not working: p159
Title: Web Development with Clojure, Third Edition - migrations/create not working: p159 When I execute the command: user=> (create-...
#question/book-web-development-with-clojure-third-edition
5 1083 2
New
lirux
PragProg Customers

The Ray Tracer Challenge: "Computing the normal on a transformed sphere" ebook test
Hi Jamis, I think there’s an issue with a test on chapter 6. I own the ebook, version P1.0 Feb. 2019. This test doesn’t pass for me: ...
#errata/book-the-ray-tracer-challenge
10 1455 5
New
jdufour
PragProg Customers

The Cucumber for Java Book:
Hello! On page xix of the preface, it says there is a community forum "… for help if your’re stuck on one of the exercises in this book… ...
#question/book-the-cucumber-for-java-book
3 1142 1
New
alanq
PragProg Customers

Modern Front-End Development for Rails: Can't get TURBO_STREAM format in some cases
This isn’t directly about the book contents so maybe not the right forum…but in some of the code apps (e.g. turbo/06) it sends a TURBO_ST...
#question/book-modern-front-end-development-for-rails
1 1369 7
New
jeremyhuiskamp
PragProg Customers

Web Development with Clojure, Third Edition (vB17.0): create table syntax invalid
Title: Web Development with Clojure, Third Edition, vB17.0 (p9) The create table guestbook syntax suggested doesn’t seem to be accepted ...
#errata/book-web-development-with-clojure-third-edition
0 1835 1
New
jskubick
PragProg Customers

Kotlin and Android Development featuring Jetpack: $kotlin_version ? (page 8)
I’m running Android Studio “Arctic Fox” 2020.3.1 Patch 2, and I’m embarrassed to admit that I only made it to page 8 before running into ...
#errata/book-kotlin-and-android-development-featuring-jetpack
0 1697 3
New
tkhobbes
PragProg Customers

Modern Front-End Development for Rails - application does not start after run bin/setup (page xviii)
After some hassle, I was able to finally run bin/setup, now I have started the rails server but I get this error message right when I vis...
#errata/book-modern-front-end-development-for-rails
0 1461 5
New
mcpierce
PragProg Customers

Kotlin and Android Development featuring Jetpack: Unique constraint error when running chapter 5 code changes
@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,...
/book-kotlin-and-android-development-featuring-jetpack
0 1165 10
New
SlowburnAZ
PragProg Customers

Machine Learning in Elixir:Error installing EXLA dependency - Page 25
Getting an error when installing the dependencies at the start of this chapter: could not compile dependency :exla, "mix compile" failed...
#errata/book-machine-learning-in-elixir
1 1133 10
New

Other popular topics Top

DevotionGeo
Backend>Chat

What is the reason behind Rust’s web framework, Rocket, not performing as well as expected in the Techempower benchmarks?
I know that these benchmarks might not be the exact picture of real-world scenario, but still I expect a Rust web framework performing a ...
#web-frameworks/rust
36 7115 11
New
Exadra37
General Dev>Hardware

What monitor(s) do you have for programming?
Please tell us what is your preferred monitor setup for programming(not gaming) and why you have chosen it. Does your monitor have eye p...
#monitors#coding#programming#development
227 10159 88
New
DevotionGeo
Backend>Chat

Would you use Erlang now when there is Elixir?
Why, if your answer is yes?
/elixir/erlang
167 4700 52
New
AstonJ
General Dev>Dev Chat

How fast do you type? Check your WPM here!
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...
typing-speed-test.aoeu.eu
/keyboards
82 7310 31
New
Exadra37
Linux>Questions

What is the most minimalist Linux server distro?
I am asking for any distro that only has the bare-bones to be able to get a shell in the server and then just install the packages as we ...
#linux#servers
66 23964 24
New
AstonJ
Backend>Chat

Rails console using 100% CPU in dev (fix)
If you are experiencing Rails console using 100% CPU on your dev machine, then updating your development and test gems might fix the issu...
/ruby/rails
3 3971 3
New
DevotionGeo
General Dev>Dev Chat

The V Programming Language
The V Programming Language Simple language for building maintainable programs V is already mentioned couple of times in the forum, but I...
#programminguages/v
21 12589 7
New
Margaret
General Dev>Dev Chat

PragProg’s Medium Posts
Hello everyone! This thread is to tell you about what authors from The Pragmatic Bookshelf are writing on Medium.
#pragprog#blog-post
1147 28379 760
New
PragmaticBookshelf
Backend>Learning Resources

Effective Haskell
Build efficient applications that exploit the unique benefits of a pure functional language, learning from an engineer who uses Haskell t...
pragprog.com
#pragprog/haskell#published-book/book-effective-haskell
15 7817 1
New
DevotionGeo
General Dev>Questions

Do you prefer regular mechanical keyboards or low profile mechanical keyboards and why?
I have always used antique keyboards like Cherry MX 1800 or Cherry MX 8100 and almost always have modified the switches in some way, like...
/keyboards#mechanical-keyboards
27 3339 9
New
Back to top

Latest in Effective Haskell

Effective Haskell Portal ❯

PragProg Customers

Pragmatic Bookshelf PragProg Customers ❯

Latest on Devtalk

Devtalk ❯

We ❤️ helpful members!

We reward our most helpful members via our MOTM scheme - by giving away a whopping 25 books per year!

Member of the Month

Devtalk Sponsors

Pragmatic Bookshelf

Practical resources that improve the lives of professional developers.

Erlang Solutions

We build trusted fault-tolerant systems that scale to billions of users.

Honeybadger

Real-time error tracking, performance insights, and observability for devs.

Manning Publications

Develop your skills with books, videos, and courses.

AppSignal

Catch errors, track performance, monitor hosts and more.

WyeWorks

Enabling companies to succeed by building software people love.

Pragmatic Studio

Courses that move you from confusion to "Aha, now I get it!"

View all our sponsors ❯

Categories:

Sub Categories:

Popular Portals

Devtalk Sponsors

Pragmatic Bookshelf

Practical resources that improve the lives of professional developers.

Erlang Solutions

We build trusted fault-tolerant systems that scale to billions of users.

Honeybadger

Real-time error tracking, performance insights, and observability for devs.

Manning Publications

Develop your skills with books, videos, and courses.

AppSignal

Catch errors, track performance, monitor hosts and more.

WyeWorks

Enabling companies to succeed by building software people love.

Pragmatic Studio

Courses that move you from confusion to "Aha, now I get it!"

View all our sponsors ❯

We're in Beta

About us Mission Statement See our Roadmap