purescript-lua · Unisay · Jun 15, 2026 · Jun 14, 2026
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -24,4 +24,7 @@ jobs:
         run: if [ -f scripts/test ]; then nix develop -c bash ./scripts/test; fi
 
       - name: Luacheck
-        run: nix develop -c luacheck --quiet --std lua51 --no-unused-args src/
+        run: nix develop -c luacheck --quiet --std lua51 --no-unused-args --max-line-length 130 src/
+
+      - name: Format check
+        run: nix fmt && git diff --exit-code
diff --git a/.gitignore b/.gitignore
@@ -1,4 +1,6 @@
 /.*
 !/.gitignore
 !/.github/
+!/.tidyrc.json
+!/.lua-format
 /output/
diff --git a/.lua-format b/.lua-format
@@ -0,0 +1,10 @@
+# LuaFormatter config for the hand-written FFI under src/.
+# 2-space indent. Keep simple functions on one line; column_limit sits a few
+# columns under luacheck's 130 limit because lua-format under-counts the leading
+# indent and trailing comma, so this keeps every emitted line within 130.
+indent_width: 2
+use_tab: false
+column_limit: 126
+continuation_indent_width: 2
+keep_simple_function_one_line: true
+keep_simple_control_block_one_line: true
diff --git a/.tidyrc.json b/.tidyrc.json
@@ -0,0 +1,10 @@
+{
+  "importSort": "source",
+  "importWrap": "source",
+  "indent": 2,
+  "operatorsFile": null,
+  "ribbon": 1,
+  "typeArrowPlacement": "first",
+  "unicode": "source",
+  "width": 80
+}
diff --git a/AGENTS.md b/AGENTS.md
@@ -4,11 +4,21 @@ A PureScript→Lua FFI fork in the [`purescript-lua`](https://github.com/purescr
 
 ## Commands
 
-All commands run inside the nix dev shell:
-
 - Build: `nix develop -c ./scripts/build`
 - Test (only if the fork has `scripts/test`): `nix develop -c bash ./scripts/test`
-- Lint: `nix develop -c luacheck --quiet --std lua51 --no-unused-args src/`
+- Lint: `nix develop -c luacheck --quiet --std lua51 --no-unused-args --max-line-length 130 src/`
+- Format: `nix fmt` (check: `nix fmt && git diff --exit-code`)
+
+## Formatting
+
+`nix fmt` runs treefmt (`treefmt.nix`): nixfmt for Nix, `dhall format`, purs-tidy
+for `*.purs` (config in `.tidyrc.json`), and LuaFormatter for the `*.lua` FFI
+(config in `.lua-format`). LuaFormatter is used over StyLua because it keeps the
+parentheses pslua's foreign-file parser requires. The Lua line budget is 130
+columns, matching the `luacheck --max-line-length` above. The check is
+content-based (`nix fmt && git diff --exit-code`) rather than `treefmt --ci`,
+since the in-place formatters bump mtime even when content is unchanged, which
+trips treefmt's `--fail-on-change`. CI and the pre-commit hook use it.
 
 ## Lua 5.1 target
 

diff --git a/bench/Main.purs b/bench/Main.purs
@@ -54,4 +54,5 @@ benchNonEmptyConversions = do
   bench = benchWith 100000
 
 loremIpsum :: String
-loremIpsum = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut aliquet euismod ligula, vitae lacinia lorem imperdiet nec. Nulla volutpat ullamcorper mollis. Proin interdum quam a sem auctor, id tempus nisl pretium. Suspendisse potenti. Quisque ut libero consequat, suscipit sem a, malesuada nisi. Aliquam dictum odio mi, eu laoreet felis scelerisque non. Ut in odio vehicula, cursus augue sed, tincidunt lorem. Vestibulum consequat lectus eu commodo vulputate. Nam vitae faucibus ipsum. Curabitur sit amet neque sed est sagittis vehicula nec nec risus. Phasellus consectetur cursus malesuada. Vestibulum commodo lorem ut mauris mollis faucibus. Integer ut massa auctor, scelerisque nisi nec, rutrum nisl. Integer vel ex sem. Sed purus felis, molestie eget cursus vel, maximus ut augue. Curabitur nunc ligula, lobortis vitae vehicula a, volutpat nec sem. Phasellus non sapien ipsum. Mauris dolor justo, mollis at elit a, sollicitudin commodo quam. Curabitur posuere felis at nunc pharetra, eu convallis lectus dapibus. Aliquam ullamcorper porta fermentum. Donec at tellus metus. Donec pharetra tempor odio sit amet viverra. Nam vel metus libero. Vivamus maximus quis lacus id pharetra. Duis sed diam molestie, sodales leo id, pulvinar justo. In non augue tempor risus consectetur hendrerit. In libero nulla, elementum non ultrices eu, vehicula non ipsum. Maecenas in hendrerit tellus, sodales dignissim turpis. Ut odio diam, convallis in elit non, consequat gravida nisi. Cras egestas metus eleifend sapien efficitur, vel vulputate est porta. Aliquam posuere, magna nec bibendum luctus, quam risus efficitur sapien, id volutpat metus ex non lorem. Praesent velit eros, efficitur sed tortor quis, lobortis eleifend ligula. Sed tellus quam, aliquet vitae sagittis a, egestas eget massa. Etiam odio elit, hendrerit vel dui vel, fermentum pharetra neque. Curabitur quis mauris id lacus consectetur rhoncus non nec mauris. Mauris blandit tempor pretium. Donec non nisi finibus, lobortis dolor vitae, euismod arcu. Nullam scelerisque lacus in dolor volutpat mollis. Nunc vitae consectetur ligula, quis laoreet quam.Proin sit amet nisi eu orci hendrerit imperdiet vitae sit amet leo. Donec sodales id ante eget viverra. Nullam vitae elit in mauris accumsan feugiat id a velit. Nulla facilisi. Cras in turpis efficitur, consectetur justo quis, suscipit tortor. Sed tincidunt pellentesque sapien, in ultricies eros rhoncus sit amet. Integer blandit ornare lobortis. Duis dictum sit amet mauris sit amet cursus. Nullam nec nisl mauris. Praesent cursus imperdiet mi mattis luctus. Donec in tortor fermentum, efficitur turpis vel, facilisis augue. Integer egestas nisl et magna volutpat ornare. Donec pulvinar risus elit, eget viverra est feugiat in.Ut nec ante vestibulum neque pulvinar pretium sit amet eu nisi. Aliquam erat volutpat. Maecenas egestas nisi et mi congue, sed ultricies nibh posuere. Suspendisse potenti. Donec a nulla et velit elementum pretium. Pellentesque gravida imperdiet sem et varius. Praesent ac diam diam. Donec iaculis risus ex, ac eleifend sapien luctus ut. Fusce aliquet, lacus tincidunt porta malesuada, massa augue commodo nulla, ac malesuada tortor est sed eros. Praesent mattis, nisi eget ullamcorper vestibulum, lacus ante placerat metus, ac ullamcorper ante tellus vel nulla. Praesent vehicula in est sit amet varius. Sed facilisis felis sed sem porttitor rutrum. Etiam sollicitudin erat neque, id gravida metus scelerisque quis. Proin venenatis pharetra lectus ac auctor."
+loremIpsum =
+  "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut aliquet euismod ligula, vitae lacinia lorem imperdiet nec. Nulla volutpat ullamcorper mollis. Proin interdum quam a sem auctor, id tempus nisl pretium. Suspendisse potenti. Quisque ut libero consequat, suscipit sem a, malesuada nisi. Aliquam dictum odio mi, eu laoreet felis scelerisque non. Ut in odio vehicula, cursus augue sed, tincidunt lorem. Vestibulum consequat lectus eu commodo vulputate. Nam vitae faucibus ipsum. Curabitur sit amet neque sed est sagittis vehicula nec nec risus. Phasellus consectetur cursus malesuada. Vestibulum commodo lorem ut mauris mollis faucibus. Integer ut massa auctor, scelerisque nisi nec, rutrum nisl. Integer vel ex sem. Sed purus felis, molestie eget cursus vel, maximus ut augue. Curabitur nunc ligula, lobortis vitae vehicula a, volutpat nec sem. Phasellus non sapien ipsum. Mauris dolor justo, mollis at elit a, sollicitudin commodo quam. Curabitur posuere felis at nunc pharetra, eu convallis lectus dapibus. Aliquam ullamcorper porta fermentum. Donec at tellus metus. Donec pharetra tempor odio sit amet viverra. Nam vel metus libero. Vivamus maximus quis lacus id pharetra. Duis sed diam molestie, sodales leo id, pulvinar justo. In non augue tempor risus consectetur hendrerit. In libero nulla, elementum non ultrices eu, vehicula non ipsum. Maecenas in hendrerit tellus, sodales dignissim turpis. Ut odio diam, convallis in elit non, consequat gravida nisi. Cras egestas metus eleifend sapien efficitur, vel vulputate est porta. Aliquam posuere, magna nec bibendum luctus, quam risus efficitur sapien, id volutpat metus ex non lorem. Praesent velit eros, efficitur sed tortor quis, lobortis eleifend ligula. Sed tellus quam, aliquet vitae sagittis a, egestas eget massa. Etiam odio elit, hendrerit vel dui vel, fermentum pharetra neque. Curabitur quis mauris id lacus consectetur rhoncus non nec mauris. Mauris blandit tempor pretium. Donec non nisi finibus, lobortis dolor vitae, euismod arcu. Nullam scelerisque lacus in dolor volutpat mollis. Nunc vitae consectetur ligula, quis laoreet quam.Proin sit amet nisi eu orci hendrerit imperdiet vitae sit amet leo. Donec sodales id ante eget viverra. Nullam vitae elit in mauris accumsan feugiat id a velit. Nulla facilisi. Cras in turpis efficitur, consectetur justo quis, suscipit tortor. Sed tincidunt pellentesque sapien, in ultricies eros rhoncus sit amet. Integer blandit ornare lobortis. Duis dictum sit amet mauris sit amet cursus. Nullam nec nisl mauris. Praesent cursus imperdiet mi mattis luctus. Donec in tortor fermentum, efficitur turpis vel, facilisis augue. Integer egestas nisl et magna volutpat ornare. Donec pulvinar risus elit, eget viverra est feugiat in.Ut nec ante vestibulum neque pulvinar pretium sit amet eu nisi. Aliquam erat volutpat. Maecenas egestas nisi et mi congue, sed ultricies nibh posuere. Suspendisse potenti. Donec a nulla et velit elementum pretium. Pellentesque gravida imperdiet sem et varius. Praesent ac diam diam. Donec iaculis risus ex, ac eleifend sapien luctus ut. Fusce aliquet, lacus tincidunt porta malesuada, massa augue commodo nulla, ac malesuada tortor est sed eros. Praesent mattis, nisi eget ullamcorper vestibulum, lacus ante placerat metus, ac ullamcorper ante tellus vel nulla. Praesent vehicula in est sit amet varius. Sed facilisis felis sed sem porttitor rutrum. Etiam sollicitudin erat neque, id gravida metus scelerisque quis. Proin venenatis pharetra lectus ac auctor."
diff --git a/flake.lock b/flake.lock
diff --git a/flake.nix b/flake.nix
@@ -9,16 +9,33 @@
       inputs.nixpkgs.follows = "nixpkgs";
     };
     pslua.url = "github:purescript-lua/purescript-lua";
+    treefmt-nix = {
+      url = "github:numtide/treefmt-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
-  outputs = { self, nixpkgs, flake-utils, purescript-overlay, pslua }:
-    flake-utils.lib.eachDefaultSystem (system:
+  outputs =
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+      purescript-overlay,
+      pslua,
+      treefmt-nix,
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
       let
         pkgs = import nixpkgs {
           inherit system;
           overlays = [ purescript-overlay.overlays.default ];
         };
-      in {
+        treefmtEval = treefmt-nix.lib.evalModule pkgs ./treefmt.nix;
+      in
+      {
+        formatter = treefmtEval.config.build.wrapper;
+        checks.formatting = treefmtEval.config.build.check self;
         devShell = pkgs.mkShell {
           buildInputs = with pkgs; [
             dhall
@@ -31,8 +48,26 @@
             spago-bin.spago-0_21_0
             treefmt
           ];
+          # Install a content-based pre-commit hook. It compares the working
+          # tree diff before and after `nix fmt`, so it only objects to changes
+          # the formatter itself introduces (not the developer's existing
+          # unstaged work) and is not fooled by formatters that only bump mtime.
+          # Rewritten each shell entry to stay in sync with this flake.
+          shellHook = ''
+            hook=.git/hooks/pre-commit
+            if [ -d .git ]; then
+              printf '%s\n' \
+                '#!/usr/bin/env bash' \
+                'before=$(git diff)' \
+                'nix fmt >/dev/null 2>&1 || exit 0' \
+                '[ "$before" = "$(git diff)" ] || { echo "nix fmt changed files; re-stage them, then commit." >&2; exit 1; }' \
+                > "$hook"
+              chmod +x "$hook"
+            fi
+          '';
         };
-      });
+      }
+    );
 
   # --- Flake Local Nix Configuration ----------------------------
   nixConfig = {

diff --git a/spago-test.dhall b/spago-test.dhall
@@ -2,8 +2,7 @@ let conf = ./spago.dhall
 
 in      conf
     //  { sources = conf.sources # [ "test/**/*.purs" ]
-        , dependencies =
-            conf.dependencies # [ "assert", "console", "effect" ]
+        , dependencies = conf.dependencies # [ "assert", "console", "effect" ]
         , backend =
             ''
             pslua \

diff --git a/src/Data/Char/Gen.purs b/src/Data/Char/Gen.purs
@@ -24,7 +24,7 @@ genDigitChar = toEnumWithDefaults bottom top <$> chooseInt 48 57
 
 -- | Generates a character from the basic latin alphabet.
 genAlpha :: forall m. MonadGen m => m Char
-genAlpha = oneOf (genAlphaLowercase :| [genAlphaUppercase])
+genAlpha = oneOf (genAlphaLowercase :| [ genAlphaUppercase ])
 
 -- | Generates a lowercase character from the basic latin alphabet.
 genAlphaLowercase :: forall m. MonadGen m => m Char

diff --git a/src/Data/String/CodePoints.lua b/src/Data/String/CodePoints.lua
@@ -4,7 +4,6 @@
 -- under this representation; every export ignores them.
 --
 -- Lua 5.1: no utf8 library, no bit operators - plain arithmetic only.
-
 -- Decodes the code point starting at byte position i.
 -- Returns the code point and the position of the next one.
 -- An invalid leading byte is returned as-is (one byte consumed).
@@ -13,22 +12,16 @@ local function decode(s, i)
   if b1 < 0x80 then return b1, i + 1 end
   if b1 >= 0xC2 and b1 <= 0xDF then
     local b2 = s:byte(i + 1)
-    if b2 and b2 >= 0x80 and b2 <= 0xBF then
-      return (b1 - 0xC0) * 0x40 + (b2 - 0x80), i + 2
-    end
+    if b2 and b2 >= 0x80 and b2 <= 0xBF then return (b1 - 0xC0) * 0x40 + (b2 - 0x80), i + 2 end
   elseif b1 >= 0xE0 and b1 <= 0xEF then
     local b2, b3 = s:byte(i + 1, i + 2)
-    if b2 and b2 >= 0x80 and b2 <= 0xBF
-      and b3 and b3 >= 0x80 and b3 <= 0xBF then
+    if b2 and b2 >= 0x80 and b2 <= 0xBF and b3 and b3 >= 0x80 and b3 <= 0xBF then
       return (b1 - 0xE0) * 0x1000 + (b2 - 0x80) * 0x40 + (b3 - 0x80), i + 3
     end
   elseif b1 >= 0xF0 and b1 <= 0xF4 then
     local b2, b3, b4 = s:byte(i + 1, i + 3)
-    if b2 and b2 >= 0x80 and b2 <= 0xBF
-      and b3 and b3 >= 0x80 and b3 <= 0xBF
-      and b4 and b4 >= 0x80 and b4 <= 0xBF then
-      return (b1 - 0xF0) * 0x40000 + (b2 - 0x80) * 0x1000
-        + (b3 - 0x80) * 0x40 + (b4 - 0x80), i + 4
+    if b2 and b2 >= 0x80 and b2 <= 0xBF and b3 and b3 >= 0x80 and b3 <= 0xBF and b4 and b4 >= 0x80 and b4 <= 0xBF then
+      return (b1 - 0xF0) * 0x40000 + (b2 - 0x80) * 0x1000 + (b3 - 0x80) * 0x40 + (b4 - 0x80), i + 4
     end
   end
   return b1, i + 1
@@ -37,28 +30,16 @@ end
 -- Encodes a code point as a UTF-8 byte string.
 local function encode(cp)
   if cp < 0x80 then return string.char(cp) end
-  if cp < 0x800 then
-    return string.char(0xC0 + math.floor(cp / 0x40), 0x80 + cp % 0x40)
-  end
+  if cp < 0x800 then return string.char(0xC0 + math.floor(cp / 0x40), 0x80 + cp % 0x40) end
   if cp < 0x10000 then
-    return string.char(
-      0xE0 + math.floor(cp / 0x1000),
-      0x80 + math.floor(cp / 0x40) % 0x40,
-      0x80 + cp % 0x40
-    )
+    return string.char(0xE0 + math.floor(cp / 0x1000), 0x80 + math.floor(cp / 0x40) % 0x40, 0x80 + cp % 0x40)
   end
-  return string.char(
-    0xF0 + math.floor(cp / 0x40000),
-    0x80 + math.floor(cp / 0x1000) % 0x40,
-    0x80 + math.floor(cp / 0x40) % 0x40,
-    0x80 + cp % 0x40
-  )
+  return string.char(0xF0 + math.floor(cp / 0x40000), 0x80 + math.floor(cp / 0x1000) % 0x40,
+                     0x80 + math.floor(cp / 0x40) % 0x40, 0x80 + cp % 0x40)
 end
 
 return {
-  _singleton = (function(_)
-    return function(cp) return encode(cp) end
-  end),
+  _singleton = (function(_) return function(cp) return encode(cp) end end),
   _fromCodePointArray = (function(_)
     return function(cps)
       local t = {}
@@ -136,5 +117,5 @@ return {
       local cp = decode(s, 1)
       return cp
     end
-  end),
+  end)
 }
diff --git a/src/Data/String/CodePoints.purs b/src/Data/String/CodePoints.purs
@@ -50,7 +50,8 @@ derive instance eqCodePoint :: Eq CodePoint
 derive instance ordCodePoint :: Ord CodePoint
 
 instance showCodePoint :: Show CodePoint where
-  show (CodePoint i) = "(CodePoint 0x" <> toUpper (toStringAs hexadecimal i) <> ")"
+  show (CodePoint i) = "(CodePoint 0x" <> toUpper (toStringAs hexadecimal i) <>
+    ")"
 
 instance boundedCodePoint :: Bounded CodePoint where
   bottom = CodePoint 0
@@ -96,9 +97,13 @@ foreign import _singleton
 singletonFallback :: CodePoint -> String
 singletonFallback (CodePoint cp) | cp <= 0xFFFF = fromCharCode cp
 singletonFallback (CodePoint cp) =
-  let lead = ((cp - 0x10000) / 0x400) + 0xD800 in
-  let trail = (cp - 0x10000) `mod` 0x400 + 0xDC00 in
-  fromCharCode lead <> fromCharCode trail
+  let
+    lead = ((cp - 0x10000) / 0x400) + 0xD800
+  in
+    let
+      trail = (cp - 0x10000) `mod` 0x400 + 0xDC00
+    in
+      fromCharCode lead <> fromCharCode trail
 
 -- | Creates a string from an array of code points. Operates in space and time
 -- | linear to the length of the array.
@@ -161,7 +166,10 @@ codePointAt :: Int -> String -> Maybe CodePoint
 codePointAt n _ | n < 0 = Nothing
 codePointAt 0 "" = Nothing
 codePointAt 0 s = Just (unsafeCodePointAt0 s)
-codePointAt n s = _codePointAt codePointAtFallback Just Nothing unsafeCodePointAt0 n s
+codePointAt n s = _codePointAt codePointAtFallback Just Nothing
+  unsafeCodePointAt0
+  n
+  s
 
 foreign import _codePointAt
   :: (Int -> String -> Maybe CodePoint)
@@ -174,7 +182,8 @@ foreign import _codePointAt
 
 codePointAtFallback :: Int -> String -> Maybe CodePoint
 codePointAtFallback n s = case uncons s of
-  Just { head, tail } -> if n == 0 then Just head else codePointAtFallback (n - 1) tail
+  Just { head, tail } ->
+    if n == 0 then Just head else codePointAtFallback (n - 1) tail
   _ -> Nothing
 
 -- | Returns a record with the first code point and the remaining code points
@@ -266,8 +275,10 @@ indexOf p s = (\i -> length (CU.take i s)) <$> CU.indexOf p s
 -- |
 indexOf' :: Pattern -> Int -> String -> Maybe Int
 indexOf' p i s =
-  let s' = drop i s in
-  (\k -> i + length (CU.take k s')) <$> CU.indexOf p s'
+  let
+    s' = drop i s
+  in
+    (\k -> i + length (CU.take k s')) <$> CU.indexOf p s'
 
 -- | Returns the number of code points preceding the last match of the given
 -- | pattern in the string. Returns `Nothing` when no matches are found.
@@ -307,8 +318,10 @@ lastIndexOf p s = (\i -> length (CU.take i s)) <$> CU.lastIndexOf p s
 -- |
 lastIndexOf' :: Pattern -> Int -> String -> Maybe Int
 lastIndexOf' p i s =
-  let i' = CU.length (take i s) in
-  (\k -> length (CU.take k s)) <$> CU.lastIndexOf' p i' s
+  let
+    i' = CU.length (take i s)
+  in
+    (\k -> length (CU.take k s)) <$> CU.lastIndexOf' p i' s
 
 -- | Returns a string containing the given number of code points from the
 -- | beginning of the given string. If the string does not have that many code
@@ -398,14 +411,17 @@ dropWhile p s = drop (countPrefix p s) s
 -- | ```
 splitAt :: Int -> String -> { before :: String, after :: String }
 splitAt i s =
-  let before = take i s in
-  { before
-  -- inline drop i s to reuse the result of take i s
-  , after: CU.drop (CU.length before) s
-  }
+  let
+    before = take i s
+  in
+    { before
+    -- inline drop i s to reuse the result of take i s
+    , after: CU.drop (CU.length before) s
+    }
 
 unsurrogate :: Int -> Int -> CodePoint
-unsurrogate lead trail = CodePoint ((lead - 0xD800) * 0x400 + (trail - 0xDC00) + 0x10000)
+unsurrogate lead trail = CodePoint
+  ((lead - 0xD800) * 0x400 + (trail - 0xDC00) + 0x10000)
 
 isLead :: Int -> Boolean
 isLead cu = 0xD800 <= cu && cu <= 0xDBFF
@@ -430,9 +446,10 @@ unsafeCodePointAt0Fallback s =
   let
     cu0 = fromEnum (Unsafe.charAt 0 s)
   in
-    if isLead cu0 && CU.length s > 1
-       then
-         let cu1 = fromEnum (Unsafe.charAt 1 s) in
-         if isTrail cu1 then unsurrogate cu0 cu1 else CodePoint cu0
-       else
-         CodePoint cu0
+    if isLead cu0 && CU.length s > 1 then
+      let
+        cu1 = fromEnum (Unsafe.charAt 1 s)
+      in
+        if isTrail cu1 then unsurrogate cu0 cu1 else CodePoint cu0
+    else
+      CodePoint cu0