外部依赖关系，Haskell，堆栈：我是否应该修改某些东西或“导入”以备足够？

Question

I am pretty new to Haskell as well as stack.

import Data.Set
import Data.Stack

The statements above trigger compilation error: Could not find module 'Data.Set'. Perhaps you meant 'Data.Int' Could not find module 'Data.Set'. Perhaps you meant 'Data.Int' . I tried to google and found nothing similar.

Hence, my question is: do I need to specify external dependencies manually or just my stack build command somewhy fails to grab appropriate modules from somewhat cache or repository?

In case I have to specify my dependencies manually, should I prefer .cabal or .yaml ? What's the correct way to deal with versioning?

Answer 1

[Do] I need to specify external dependencies manually [...]?

Yes.

Since you are using Stack, it is easy to specify the dependent packages you import in your code. Depend on your Stack version, the default configuration might be a little bit different:

1. If you created your project with the latest version of Stack, you will see package.yaml in the root of your project ( hpack is used in this case to specify the configurations). You need to add package dependencies there, eg, containers for Data.Set . Here's an example of a dependencies section in one of my projects:

    dependencies: - base >= 4.7 && < 5 - containers - time - network - bytestring 

2. If you are using an older version of stack and do not see package.yaml , you need to edit your-project-name.cabal to add the dependencies. Here's the complete document telling you how to do it: https://docs.haskellstack.org/en/stable/GUIDE/#adding-dependencies

Personally, I prefer the new system with hpack ( package.yaml ). Basically, it is simpler, and it saves you time declaring all modules you have (not about dependency). If you have package.yaml , do not edit .cabal , which is automatically generated by hpack .