ndmitchell / ndmitchell/hlint

Can't annotate data type

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Dominant language
Haskell
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Description

I want to ignore the "Use newtype instead of data" rule for a single line, like

{-# ANN Person "HLint: ignore Use newtype instead of data" #-}
data Person
  = Employee Int
  -- TODO: add Boss

But then GHC errors with Not in scope: data constructor 'Person'. If I try annotating the Employee constructor, then the hlint annotation doesn't suppress the rule anymore.

Workaround for now is to just ignore the rule in the entire module. Is there a better solution for this?

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the ANN Person example and its GHC “Not in scope” error, then compare it with annotating the Employee constructor. Investigate how HLint interprets these annotations and define a solution that suppresses only the Use newtype instead of data rule for the declaration without requiring a module-wide ignore.

Written by the indexing model from the issue text.

Assessment

Tech stack
haskell
Domain
tooling
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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