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

abtin
page 20: … protoc command… I had to additionally run the following go get commands in order to be able to compile protobuf code using go...
New
jimmykiang
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:...
New
New
johnp
Running the examples in chapter 5 c under pytest 5.4.1 causes an AttributeError: ‘module’ object has no attribute ‘config’. In particula...
New
AleksandrKudashkin
On the page xv there is an instruction to run bin/setup from the main folder. I downloaded the source code today (12/03/21) and can’t see...
New
brian-m-ops
#book-python-testing-with-pytest-second-edition Hi. Thanks for writing the book. I am just learning so this might just of been an issue ...
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
Keton
When running the program in chapter 8, “Implementing Combat”, the printout Health before attack was never printed so I assumed something ...
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
New

Other popular topics Top

PragmaticBookshelf
Machine learning can be intimidating, with its reliance on math and algorithms that most programmers don't encounter in their regular wor...
New
PragmaticBookshelf
Brace yourself for a fun challenge: build a photorealistic 3D renderer from scratch! In just a couple of weeks, build a ray tracer that r...
New
Exadra37
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...
New
PragmaticBookshelf
Rust is an exciting new programming language combining the power of C with memory safety, fearless concurrency, and productivity boosters...
New
AstonJ
This looks like a stunning keycap set :orange_heart: A LEGENDARY KEYBOARD LIVES ON When you bought an Apple Macintosh computer in the e...
New
mafinar
This is going to be a long an frequently posted thread. While talking to a friend of mine who has taken data structure and algorithm cou...
New
PragmaticBookshelf
Build efficient applications that exploit the unique benefits of a pure functional language, learning from an engineer who uses Haskell t...
New
PragmaticBookshelf
Author Spotlight Rebecca Skinner @RebeccaSkinner Welcome to our latest author spotlight, where we sit down with Rebecca Skinner, auth...
New
DevotionGeo
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...
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: