pennychase

pennychase

Effective Haskell (Chapter 2 - pp. 51 and 54 in ePub)

In the “Filtering List Elements” section, the party budget function is first called “foodBudget” and all subsequent reference are “partyBudget”.

I filled in the implementation of the list comprehension version of partyBudget and was surprised at the result when two people in the guest list had the same food, but willEat for one person was false: the result was twice the food. Duh, of course that’s because of the non-determinism of list comprehensions (the permutations from peeling off the fst and snd elements of the tuples). The Roman Numeral example touches on this, but I wonder if there could be a bit more explicit discussion of what’s going on when there are multiple lists as generators in list comprehensions.

First Post!

RebeccaSkinner

RebeccaSkinner

Author of Effective Haskell

Thanks for bringing this to my attention, I’ll see if I can make that a bit more clear!

Where Next?

Popular Pragmatic Bookshelf topics Top

simonpeter
When I try the command to create a pair of migration files I get an error. user=> (create-migration "guestbook") Execution error (Ill...
New
jdufour
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… ...
New
curtosis
Running mix deps.get in the sensor_hub directory fails with the following error: ** (Mix) No SSH public keys found in ~/.ssh. An ssh aut...
New
Charles
In general, the book isn’t yet updated for Phoenix version 1.6. On page 18 of the book, the authors indicate that an auto generated of ro...
New
brunogirin
When trying to run tox in parallel as explained on page 151, I got the following error: tox: error: argument -p/–parallel: expected one...
New
hazardco
On page 78 the following code appears: <%= link_to ‘Destroy’, product, class: ‘hover:underline’, method: :delete, data: { confirm...
New
s2k
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
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
a.zampa
@mfazio23 I’m following the indications of the book and arriver ad chapter 10, but the app cannot be compiled due to an error in the Bas...
New
bjnord
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

Other popular topics Top

New
AstonJ
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
Margaret
Hello content creators! Happy new year. What tech topics do you think will be the focus of 2021? My vote for one topic is ethics in tech...
New
PragmaticBookshelf
Learn different ways of writing concurrent code in Elixir and increase your application's performance, without sacrificing scalability or...
New
wmnnd
Here’s the story how one of the world’s first production deployments of LiveView came to be - and how trying to improve it almost caused ...
New
foxtrottwist
A few weeks ago I started using Warp a terminal written in rust. Though in it’s current state of development there are a few caveats (tab...
New
AstonJ
We’ve talked about his book briefly here but it is quickly becoming obsolete - so he’s decided to create a series of 7 podcasts, the firs...
New
First poster: bot
Large Language Models like ChatGPT say The Darnedest Things. The Errors They MakeWhy We Need to Document Them, and What We Have Decided ...
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
AnfaengerAlex
Hello, I’m a beginner in Android development and I’m facing an issue with my project setup. In my build.gradle.kts file, I have the foll...
New

Sub Categories: