From 5aeea4ee13d741fb8b27a290bd05f1dce2c95a50 Mon Sep 17 00:00:00 2001
From: Sridhar Ratnakumar <3998+srid@users.noreply.github.com>
Date: Wed, 5 Nov 2025 19:28:55 -0500
Subject: [PATCH] haskell: relude

---
 flake.lock                                    |  6 +-
 .../home/claude-code/skills/haskell/SKILL.md  | 76 +++++++++++++++++++
 2 files changed, 79 insertions(+), 3 deletions(-)

diff --git a/flake.lock b/flake.lock
index ae00f09..4d660cc 100644
--- a/flake.lock
+++ b/flake.lock
@@ -1137,11 +1137,11 @@
         "warp-tls-simple": "warp-tls-simple"
       },
       "locked": {
-        "lastModified": 1762373149,
-        "narHash": "sha256-cPeMJ+rr3V7PjnNHX10NXeNv/rL7MNy3PkTXyut5sko=",
+        "lastModified": 1762375154,
+        "narHash": "sha256-Kju32XBfrcIqxbsD20xwsjBkGJXCuDVrMLcFwog2hAw=",
         "owner": "juspay",
         "repo": "vira",
-        "rev": "504f7205c6079e8dd04feb5422cb92eba657cb1d",
+        "rev": "8e1aa3ca45f7dfb5981960e7710738d447b7fede",
         "type": "github"
       },
       "original": {
diff --git a/modules/home/claude-code/skills/haskell/SKILL.md b/modules/home/claude-code/skills/haskell/SKILL.md
index 61fbaac..38773d8 100644
--- a/modules/home/claude-code/skills/haskell/SKILL.md
+++ b/modules/home/claude-code/skills/haskell/SKILL.md
@@ -36,6 +36,82 @@ Every error case in generated code must be handled properly.
 - Use `Applicative` and `Monad` appropriately
 - Avoid trivial `let` bindings when inlining keeps code simple and readable
 
+## HLint
+
+**IMPORTANT**: Always check if the project has a `.hlint.yaml` file. If it does:
+1. Read the `.hlint.yaml` file to understand project-specific style rules
+2. Follow all recommendations in that file when writing code
+3. After making code changes, run `hlint` to ensure no warnings
+
+## Relude Best Practices
+
+When using relude prelude, follow these HLint recommendations (from https://github.com/kowainik/relude/blob/main/.hlint.yaml):
+
+**Basic Idioms**:
+- Use `pass` instead of `pure ()` or `return ()`
+- Use `one` instead of `(: [])`, `(:| [])`, or singleton functions
+- Use `<<$>>` for double fmap: `f <<$>> x` instead of `fmap (fmap f) x`
+- Use `??` (flap) operator: `ff ?? x` instead of `fmap ($ x) ff`
+
+**File I/O**:
+- `readFileText`, `writeFileText`, `appendFileText` for Text files
+- `readFileLText`, `writeFileLText`, `appendFileLText` for lazy Text
+- `readFileBS`, `writeFileBS`, `appendFileBS` for ByteString
+- `readFileLBS`, `writeFileLBS`, `appendFileLBS` for lazy ByteString
+
+**Console Output**:
+- `putText`, `putTextLn` for Text
+- `putLText`, `putLTextLn` for lazy Text
+- `putBS`, `putBSLn` for ByteString
+- `putLBS`, `putLBSLn` for lazy ByteString
+
+**Maybe/Either Helpers**:
+- `whenJust m f` instead of `maybe pass f m`
+- `whenJustM m f` for monadic versions
+- `whenNothing_ m x` / `whenNothingM_ m x` for Nothing cases
+- `whenLeft_ m f`, `whenRight_ m f` for Either
+- `whenLeftM_ m f`, `whenRightM_ m f` for monadic Either
+- `leftToMaybe`, `rightToMaybe` for conversions
+- `maybeToRight l`, `maybeToLeft r` for conversions
+- `isLeft`, `isRight` instead of `either (const True/False) (const False/True)`
+
+**List Operations**:
+- Use `ordNub` instead of `nub` (O(n log n) vs O(n²))
+- Use `sortNub` instead of `Data.Set.toList . Data.Set.fromList`
+- Use `sortWith f` instead of `sortBy (comparing f)` for simple cases
+- Use `viaNonEmpty f x` instead of `fmap f (nonEmpty x)`
+- Use `asumMap f xs` instead of `asum (map f xs)`
+- Use `toList` instead of `foldr (:) []`
+
+**Monadic Operations**:
+- `andM s` instead of `and <$> sequence s`
+- `orM s` instead of `or <$> sequence s`
+- `allM f s` instead of `and <$> mapM f s`
+- `anyM f s` instead of `or <$> mapM f s`
+- `guardM f` instead of `f >>= guard`
+- `infinitely` instead of `forever` (better typed)
+- `unlessM (not <$> x)` → use `whenM x` instead
+- `whenM (not <$> x)` → use `unlessM x` instead
+
+**State/Reader Operations**:
+- `usingReaderT` instead of `flip runReaderT`
+- `usingStateT` instead of `flip runStateT`
+- `evaluatingStateT s st` instead of `fst <$> usingStateT s st`
+- `executingStateT s st` instead of `snd <$> usingStateT s st`
+
+**Transformer Lifting**:
+- `hoistMaybe m` instead of `MaybeT (pure m)`
+- `hoistEither m` instead of `ExceptT (pure m)`
+
+**List Pattern Matching**:
+- `whenNotNull m f` for `case m of [] -> pass; (x:xs) -> f (x :| xs)`
+- `whenNotNullM m f` for monadic version
+
+**Text/ByteString Conversions**:
+- Use relude's `toText`, `toString`, `toLText` instead of pack/unpack
+- Use relude's `encodeUtf8`, `decodeUtf8` for UTF-8 encoding
+- `fromStrict`, `toStrict` for lazy/strict conversions
+
 ## Testing
 
 - Use QuickCheck for property-based testing