Question 1

How to ignore a specific hint in HLint?

Accepted Answer

You can use pragmas like {-# HLINT ignore "Eta reduce" #-} in your code or add ignore directives in .hlint.yaml, such as - ignore: {name: "Eta reduce"}, to suppress hints globally or per-module.

Question 2

HLint vs GHC's -Wall: which is better for code style?

Accepted Answer

HLint focuses on stylistic improvements and idiomatic patterns, suggesting simplifications like using concatMap, while GHC's -Wall catches compiler warnings like unused imports. They complement each other, with HLint being more opinionated on style.

Question 3

How to add custom hints to HLint?

Accepted Answer

Define new hints in a .hlint.yaml file using YAML syntax, e.g., - warn: {lhs: concat (map f x), rhs: concatMap f x}. You can also use --find to generate hints from existing code.

Question 4

Why does HLint not parse my code with QuasiQuotes?

Accepted Answer

HLint enables many extensions by default but may need explicit flags. Add - arguments: [-XQuasiQuotes] to your .hlint.yaml to enable specific extensions, as parsing can fail otherwise.

Question 5

How to run HLint automatically in continuous integration?

Accepted Answer

Use provided scripts like curl -sSL https://raw.github.com/ndmitchell/hlint/master/misc/run.sh | sh -s . for Travis, or integrate with GitHub Actions using haskell-actions/hlint-scan, as detailed in the CI section.

Question 6

Can HLint refactor code automatically?

Accepted Answer

Yes, with the --refactor flag and the apply-refact tool installed, HLint can automatically apply some suggestions, but not all hints support refactoring—check hints.md for limitations.

HLint

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