PragProg Customers

Effective Haskell: ch2 combineLists (page 66)

juhp

juhp

Effective Haskell: ch2 combineLists (page 66)

On p66 of B9.0 chapter 2:

combineLists as bs = 
  let a = head as
      b = head bs
      as' = tail as
      bs' = tail bs
  in if null as || null bs
     then []
     else (a,b) : combineLists as' bs'

I find this let clause a bit of an eyesore given that head and tail are not safe.

How about moving the let clause into the else branch (or possibly a where)? Or is it better just to drop those local variables completely?

1 comment
#errata/book-effective-haskell
0 421 1

First Post!

RebeccaSkinner

RebeccaSkinner

Author of Effective Haskell

Thanks. It’s sometimes hard to figure out how to format these early examples. I think being verbosely explicit here helps people build an intuition up.

Post #2

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
0 421 1
Last post

Popular Pragmatic Bookshelf topics Top

jimmykiang
PragProg Customers

Distributed Services With Go - Agent_test.go error line 77
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:...
#errata/book-distributed-services-with-go
4 1559 7
New
edruder
PragProg Customers

Docker for Rails Developers: Notes for Rails 6.1, Ruby 2.7.2
I thought that there might be interest in using the book with Rails 6.1 and Ruby 2.7.2. I’ll note what I needed to do differently here. ...
/book-docker-for-rails-developers
9 1177 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 1386 7
New
patoncrispy
PragProg Customers

Hands-on Rust: Adequate docs for bracket_lib
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...
#question/book-hands-on-rust
5 1516 3
New
jskubick
PragProg Customers

Kotlin and Android Development featuring Jetpack: SwitchCompat's thumbTint and trackTint being ignored (page 76)
I think I might have found a problem involving SwitchCompat, thumbTint, and trackTint. As entered, the SwitchCompat changes color to hol...
#errata/book-kotlin-and-android-development-featuring-jetpack
0 2749 2
New
digitalbias
PragProg Customers

Build a Weather Station with Elixir and Nerves: Problem connecting to Postgres with Grafana
Title: Build a Weather Station with Elixir and Nerves: Problem connecting to Postgres with Grafana on (page 64) If you follow the defau...
#errata/book-build-a-weather-station-with-elixir-and-nerves
0 1962 4
New
brunogirin
PragProg Customers

Python Testing with pytest, Second Edition: error when installing editable package (page 178)
When installing Cards as an editable package, I get the following error: ERROR: File “setup.py” not found. Directory cannot be installe...
#errata/book-python-testing-with-pytest-second-edition
0 1739 1
New
kolossal
PragProg Customers

Hands on Rust: Need help with error - thread 'main' panicked at 'Failed to load texture
Hi, I need some help, I’m new to rust and was learning through your book. but I got stuck at the last stage of distribution. Whenever I t...
#question/book-hands-on-rust
3 1989 5
New
ggerico
PragProg Customers

Programming Machine Learning: some plot files are throwing error
I got this error when executing the plot files on macOS Ventura 13.0.1 with Python 3.10.8 and matplotlib 3.6.1: programming_ML/code/03_...
#question/book-programming-machine-learning
1 3055 5
New
gorkaio
PragProg Customers

Programming Phoenix LiveView: PentoWeb.LayoutView errata (56)
root_layout: {PentoWeb.LayoutView, :root}, This results in the following following error: no “root” html template defined for PentoWeb...
#errata/book-programming-phoenix-liveview
8 1094 4
New

Other popular topics Top

PragmaticBookshelf
General Dev>Learning Resources

Forge Your Future with Open Source
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...
pragprog.com
#pragprog#published-book/book-forge-your-future-with-open-source
3 5654 0
New
PragmaticBookshelf
Data Science

Genetic Algorithms in Elixir
From finance to artificial intelligence, genetic algorithms are a powerful tool with a wide array of applications. But you don't need an ...
#pragprog#ai/elixir#published-book/book-genetic-algorithms-in-elixir
25 5243 6
New
dimitarvp
macOS>Chat

My thoughts on macOS vs Linux
Small essay with thoughts on macOS vs. Linux: I know @Exadra37 is just waiting around the corner to scream at me “I TOLD YOU SO!!!” but I...
#macos#linux
166 9730 69
New
Exadra37
Linux>Chat

RancherOS is in end of life
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...
#linux#rancheros
10 6358 6
New
PragmaticBookshelf
Community>In The Spotlight

Spotlight: Jamis Buck (Author) Interview and AMA!
Author Spotlight Jamis Buck @jamis This month, we have the pleasure of spotlighting author Jamis Buck, who has written Mazes for Prog...
#author-spotlight/ruby/book-the-ray-tracer-challenge/book-mazes-for-programmers
21 6352 9
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 3877 9
New
PragmaticBookshelf
General Dev>Learning Resources

A Common-Sense Guide to Data Structures and Algorithms in Python, Volume 1
Big O Notation can make your code faster by orders of magnitude. Get the hands-on info you need to master data structures and algorithms ...
pragprog.com
#pragprog/python#published-book/book-a-common-sense-guide-to-data-structures-and-algorithms-in-python-volume-1
24 5988 11
New
PragmaticBookshelf
Backend>Learning Resources

MySQL 9 Essentials
A concise guide to MySQL 9 database administration, covering fundamental concepts, techniques, and best practices. Neil Smyth MySQL...
pragprog.com
#pragprog#published-book/mysql/book-mysql-9-essentials
2 4162 0
New
mindriot
General Dev>Reviews

Keyboard Review: UHK60V2 vs Defy vs Voyager vs Glove80 vs Svalboard
Ok, well here are some thoughts and opinions on some of the ergonomic keyboards I have, I guess like mini review of each that I use enoug...
/keyboards#uhk60v2#defy#voyager#glove80#svalboard
5 5681 7
New
PragmaticBookshelf
Backend>Learning Resources

Risk-First Software Development, Second Edition
As digital systems increasingly run the world, mastery of the recurring patterns of software development risk is the key to fast and effe...
pragprog.com
#pragprog#published-book/book-risk-first-software-development-second-edition
12 4217 8
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.

EEF

Supporting innovation across the BEAM ecosystem.

coders51

We build reliable cloud platforms for business-critical systems.

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!"

Linux New Media

Publishing Linux Magazine, ADMIN, and MakerSpace for 25+ years.

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.

EEF

Supporting innovation across the BEAM ecosystem.

coders51

We build reliable cloud platforms for business-critical systems.

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!"

Linux New Media

Publishing Linux Magazine, ADMIN, and MakerSpace for 25+ years.

View all our sponsors ❯

We're in Beta

About us Mission Statement See our Roadmap