diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d624d2e..4dc2d20 100644
--- 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
index db67e9a..e070528 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,6 @@
 /.*
 !/.gitignore
 !/.github/
+!/.tidyrc.json
+!/.lua-format
 /output/
diff --git a/.lua-format b/.lua-format
new file mode 100644
index 0000000..2945014
--- /dev/null
+++ 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
new file mode 100644
index 0000000..8636af8
--- /dev/null
+++ 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
index dde531a..a312901 100644
--- 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/flake.lock b/flake.lock
index 6b6c417..c47b792 100644
--- a/flake.lock
+++ b/flake.lock
@@ -740,7 +740,8 @@
         "flake-utils": "flake-utils",
         "nixpkgs": "nixpkgs",
         "pslua": "pslua",
-        "purescript-overlay": "purescript-overlay"
+        "purescript-overlay": "purescript-overlay",
+        "treefmt-nix": "treefmt-nix"
       }
     },
     "stackage": {
@@ -803,6 +804,26 @@
         "repo": "default",
         "type": "github"
       }
+    },
+    "treefmt-nix": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1780220602,
+        "narHash": "sha256-eynAfOmbmxJnkp7YewvCEbShNnnYJ9gLLqkzsYtBPeM=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "db947814a175b7ca6ded66e21383d938df01c227",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
     }
   },
   "root": "root",
diff --git a/flake.nix b/flake.nix
index 5198865..4d86c4b 100644
--- 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.dhall b/spago.dhall
index 63bbe49..454a951 100644
--- a/spago.dhall
+++ b/spago.dhall
@@ -1,5 +1,5 @@
 { name = "purescript-lua-effect"
-, dependencies = [ "prelude" ] 
+, dependencies = [ "prelude" ]
 , packages = ./packages.dhall
 , sources = [ "src/**/*.purs" ]
 , backend =
diff --git a/src/Effect.lua b/src/Effect.lua
index 3f06cf7..9d2736a 100644
--- a/src/Effect.lua
+++ b/src/Effect.lua
@@ -1,49 +1,8 @@
 return {
-  pureE = (function(a)
-    return function()
-      return a
-    end
-  end),
-  bindE = (function(a)
-    return function(f)
-      return function()
-        return f(a())()
-      end
-    end
-  end),
-  untilE = (function(f)
-    return function()
-      while not f() do
-      end
-    end
-  end),
-  whileE = (function(f)
-    return function(a)
-      return function()
-        while f() do
-          a()
-        end
-      end
-    end
-  end),
-  forE = (function(lo)
-    return function(hi)
-      return function(f)
-        return function()
-          for i = lo, hi do
-            f(i)()
-          end
-        end
-      end
-    end
-  end),
-  foreachE = (function(as)
-    return function(f)
-      return function()
-        for i = 1, #as do
-          f(as[i])()
-        end
-      end
-    end
-  end)
+  pureE = (function(a) return function() return a end end),
+  bindE = (function(a) return function(f) return function() return f(a())() end end end),
+  untilE = (function(f) return function() while not f() do end end end),
+  whileE = (function(f) return function(a) return function() while f() do a() end end end end),
+  forE = (function(lo) return function(hi) return function(f) return function() for i = lo, hi do f(i)() end end end end end),
+  foreachE = (function(as) return function(f) return function() for i = 1, #as do f(as[i])() end end end end)
 }
diff --git a/src/Effect.purs b/src/Effect.purs
index 32ea342..cbae24c 100644
--- a/src/Effect.purs
+++ b/src/Effect.purs
@@ -3,7 +3,10 @@
 -- | computations, while at the same time generating efficient JavaScript.
 module Effect
   ( Effect
-  , untilE, whileE, forE, foreachE
+  , untilE
+  , whileE
+  , forE
+  , foreachE
   ) where
 
 import Prelude
@@ -69,4 +72,5 @@ foreign import forE :: Int -> Int -> (Int -> Effect Unit) -> Effect Unit
 -- |
 -- | `foreachE xs f` runs the computation returned by the function `f` for each
 -- | of the inputs `xs`.
-foreign import foreachE :: forall a. Array a -> (a -> Effect Unit) -> Effect Unit
+foreign import foreachE
+  :: forall a. Array a -> (a -> Effect Unit) -> Effect Unit
diff --git a/src/Effect/Uncurried.lua b/src/Effect/Uncurried.lua
index 01acec5..b1cf78b 100644
--- a/src/Effect/Uncurried.lua
+++ b/src/Effect/Uncurried.lua
@@ -1,106 +1,28 @@
 return {
-  mkEffectFn1 = (function(fn)
-    return function(a)
-      return fn(a)()
-    end
-  end),
-  mkEffectFn2 = (function(fn)
-    return function(a, b)
-      return fn(a)(b)()
-    end
-  end),
-  mkEffectFn3 = (function(fn)
-    return function(a, b, c)
-      return fn(a)(b)(c)()
-    end
-  end),
-  mkEffectFn4 = (function(fn)
-    return function(a, b, c, d)
-      return fn(a)(b)(c)(d)()
-    end
-  end),
-  mkEffectFn5 = (function(fn)
-    return function(a, b, c, d, e)
-      return fn(a)(b)(c)(d)(e)()
-    end
-  end),
-  mkEffectFn6 = (function(fn)
-    return function(a, b, c, d, e, f)
-      return fn(a)(b)(c)(d)(e)(f)()
-    end
-  end),
-  mkEffectFn7 = (function(fn)
-    return function(a, b, c, d, e, f, g)
-      return fn(a)(b)(c)(d)(e)(f)(g)()
-    end
-  end),
-  mkEffectFn8 = (function(fn)
-    return function(a, b, c, d, e, f, g, h)
-      return fn(a)(b)(c)(d)(e)(f)(g)(h)()
-    end
-  end),
-  mkEffectFn9 = (function(fn)
-    return function(a, b, c, d, e, f, g, h, i)
-      return fn(a)(b)(c)(d)(e)(f)(g)(h)(i)()
-    end
-  end),
-  mkEffectFn10 = (function(fn)
-    return function(a, b, c, d, e, f, g, h, i, j)
-      return fn(a)(b)(c)(d)(e)(f)(g)(h)(i)(j)()
-    end
-  end),
-  runEffectFn1 = (function(fn)
-    return function(a)
-      return function()
-        return fn(a)
-      end
-    end
-  end),
-  runEffectFn2 = (function(fn)
-    return function(a)
-      return function(b)
-        return function()
-          return fn(a, b)
-        end
-      end
-    end
-  end),
+  mkEffectFn1 = (function(fn) return function(a) return fn(a)() end end),
+  mkEffectFn2 = (function(fn) return function(a, b) return fn(a)(b)() end end),
+  mkEffectFn3 = (function(fn) return function(a, b, c) return fn(a)(b)(c)() end end),
+  mkEffectFn4 = (function(fn) return function(a, b, c, d) return fn(a)(b)(c)(d)() end end),
+  mkEffectFn5 = (function(fn) return function(a, b, c, d, e) return fn(a)(b)(c)(d)(e)() end end),
+  mkEffectFn6 = (function(fn) return function(a, b, c, d, e, f) return fn(a)(b)(c)(d)(e)(f)() end end),
+  mkEffectFn7 = (function(fn) return function(a, b, c, d, e, f, g) return fn(a)(b)(c)(d)(e)(f)(g)() end end),
+  mkEffectFn8 = (function(fn) return function(a, b, c, d, e, f, g, h) return fn(a)(b)(c)(d)(e)(f)(g)(h)() end end),
+  mkEffectFn9 = (function(fn) return function(a, b, c, d, e, f, g, h, i) return fn(a)(b)(c)(d)(e)(f)(g)(h)(i)() end end),
+  mkEffectFn10 = (function(fn) return function(a, b, c, d, e, f, g, h, i, j) return fn(a)(b)(c)(d)(e)(f)(g)(h)(i)(j)() end end),
+  runEffectFn1 = (function(fn) return function(a) return function() return fn(a) end end end),
+  runEffectFn2 = (function(fn) return function(a) return function(b) return function() return fn(a, b) end end end end),
   runEffectFn3 = (function(fn)
-    return function(a)
-      return function(b)
-        return function(c)
-          return function()
-            return fn(a, b, c)
-          end
-        end
-      end
-    end
+    return function(a) return function(b) return function(c) return function() return fn(a, b, c) end end end end
   end),
   runEffectFn4 = (function(fn)
     return function(a)
-      return function(b)
-        return function(c)
-          return function(d)
-            return function()
-              return fn(a, b, c, d)
-            end
-          end
-        end
-      end
+      return function(b) return function(c) return function(d) return function() return fn(a, b, c, d) end end end end
     end
   end),
   runEffectFn5 = (function(fn)
     return function(a)
       return function(b)
-        return function(c)
-          return function(d)
-            return function(e)
-              return function()
-                return fn(a, b, c, d, e)
-              end
-            end
-          end
-        end
+        return function(c) return function(d) return function(e) return function() return fn(a, b, c, d, e) end end end end
       end
     end
   end),
@@ -109,13 +31,7 @@ return {
       return function(b)
         return function(c)
           return function(d)
-            return function(e)
-              return function(f)
-                return function()
-                  return fn(a, b, c, d, e, f)
-                end
-              end
-            end
+            return function(e) return function(f) return function() return fn(a, b, c, d, e, f) end end end
           end
         end
       end
@@ -127,13 +43,7 @@ return {
         return function(c)
           return function(d)
             return function(e)
-              return function(f)
-                return function(g)
-                  return function()
-                    return fn(a, b, c, d, e, f, g)
-                  end
-                end
-              end
+              return function(f) return function(g) return function() return fn(a, b, c, d, e, f, g) end end end
             end
           end
         end
@@ -148,11 +58,7 @@ return {
             return function(e)
               return function(f)
                 return function(g)
-                  return function(h)
-                    return function()
-                      return fn(a, b, c, d, e, f, g, h)
-                    end
-                  end
+                  return function(h) return function() return fn(a, b, c, d, e, f, g, h) end end
                 end
               end
             end
@@ -170,11 +76,7 @@ return {
               return function(f)
                 return function(g)
                   return function(h)
-                    return function(i)
-                      return function()
-                        return fn(a, b, c, d, e, f, g, h, i)
-                      end
-                    end
+                    return function(i) return function() return fn(a, b, c, d, e, f, g, h, i) end end
                   end
                 end
               end
@@ -194,11 +96,7 @@ return {
                 return function(g)
                   return function(h)
                     return function(i)
-                      return function(j)
-                        return function()
-                          return fn(a, b, c, d, e, f, g, h, i, j)
-                        end
-                      end
+                      return function(j) return function() return fn(a, b, c, d, e, f, g, h, i, j) end end
                     end
                   end
                 end
diff --git a/src/Effect/Uncurried.purs b/src/Effect/Uncurried.purs
index 7ed42e8..3f1ee27 100644
--- a/src/Effect/Uncurried.purs
+++ b/src/Effect/Uncurried.purs
@@ -151,71 +151,220 @@ foreign import data EffectFn4 :: Type -> Type -> Type -> Type -> Type -> Type
 
 type role EffectFn4 representational representational representational representational representational
 
-foreign import data EffectFn5 :: Type -> Type -> Type -> Type -> Type -> Type -> Type
+foreign import data EffectFn5
+  :: Type -> Type -> Type -> Type -> Type -> Type -> Type
 
 type role EffectFn5 representational representational representational representational representational representational
 
-foreign import data EffectFn6 :: Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type
+foreign import data EffectFn6
+  :: Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type
 
 type role EffectFn6 representational representational representational representational representational representational representational
 
-foreign import data EffectFn7 :: Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type
+foreign import data EffectFn7
+  :: Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type
 
 type role EffectFn7 representational representational representational representational representational representational representational representational
 
-foreign import data EffectFn8 :: Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type
+foreign import data EffectFn8
+  :: Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
 
 type role EffectFn8 representational representational representational representational representational representational representational representational representational
 
-foreign import data EffectFn9 :: Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type
+foreign import data EffectFn9
+  :: Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
 
 type role EffectFn9 representational representational representational representational representational representational representational representational representational representational
 
-foreign import data EffectFn10 :: Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type -> Type
+foreign import data EffectFn10
+  :: Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
+  -> Type
 
 type role EffectFn10 representational representational representational representational representational representational representational representational representational representational representational
 
-foreign import mkEffectFn1 :: forall a r.
-  (a -> Effect r) -> EffectFn1 a r
-foreign import mkEffectFn2 :: forall a b r.
-  (a -> b -> Effect r) -> EffectFn2 a b r
-foreign import mkEffectFn3 :: forall a b c r.
-  (a -> b -> c -> Effect r) -> EffectFn3 a b c r
-foreign import mkEffectFn4 :: forall a b c d r.
-  (a -> b -> c -> d -> Effect r) -> EffectFn4 a b c d r
-foreign import mkEffectFn5 :: forall a b c d e r.
-  (a -> b -> c -> d -> e -> Effect r) -> EffectFn5 a b c d e r
-foreign import mkEffectFn6 :: forall a b c d e f r.
-  (a -> b -> c -> d -> e -> f -> Effect r) -> EffectFn6 a b c d e f r
-foreign import mkEffectFn7 :: forall a b c d e f g r.
-  (a -> b -> c -> d -> e -> f -> g -> Effect r) -> EffectFn7 a b c d e f g r
-foreign import mkEffectFn8 :: forall a b c d e f g h r.
-  (a -> b -> c -> d -> e -> f -> g -> h -> Effect r) -> EffectFn8 a b c d e f g h r
-foreign import mkEffectFn9 :: forall a b c d e f g h i r.
-  (a -> b -> c -> d -> e -> f -> g -> h -> i -> Effect r) -> EffectFn9 a b c d e f g h i r
-foreign import mkEffectFn10 :: forall a b c d e f g h i j r.
-  (a -> b -> c -> d -> e -> f -> g -> h -> i -> j -> Effect r) -> EffectFn10 a b c d e f g h i j r
-
-foreign import runEffectFn1 :: forall a r.
-  EffectFn1 a r -> a -> Effect r
-foreign import runEffectFn2 :: forall a b r.
-  EffectFn2 a b r -> a -> b -> Effect r
-foreign import runEffectFn3 :: forall a b c r.
-  EffectFn3 a b c r -> a -> b -> c -> Effect r
-foreign import runEffectFn4 :: forall a b c d r.
-  EffectFn4 a b c d r -> a -> b -> c -> d -> Effect r
-foreign import runEffectFn5 :: forall a b c d e r.
-  EffectFn5 a b c d e r -> a -> b -> c -> d -> e -> Effect r
-foreign import runEffectFn6 :: forall a b c d e f r.
-  EffectFn6 a b c d e f r -> a -> b -> c -> d -> e -> f -> Effect r
-foreign import runEffectFn7 :: forall a b c d e f g r.
-  EffectFn7 a b c d e f g r -> a -> b -> c -> d -> e -> f -> g -> Effect r
-foreign import runEffectFn8 :: forall a b c d e f g h r.
-  EffectFn8 a b c d e f g h r -> a -> b -> c -> d -> e -> f -> g -> h -> Effect r
-foreign import runEffectFn9 :: forall a b c d e f g h i r.
-  EffectFn9 a b c d e f g h i r -> a -> b -> c -> d -> e -> f -> g -> h -> i -> Effect r
-foreign import runEffectFn10 :: forall a b c d e f g h i j r.
-  EffectFn10 a b c d e f g h i j r -> a -> b -> c -> d -> e -> f -> g -> h -> i -> j -> Effect r
+foreign import mkEffectFn1
+  :: forall a r
+   . (a -> Effect r)
+  -> EffectFn1 a r
+
+foreign import mkEffectFn2
+  :: forall a b r
+   . (a -> b -> Effect r)
+  -> EffectFn2 a b r
+
+foreign import mkEffectFn3
+  :: forall a b c r
+   . (a -> b -> c -> Effect r)
+  -> EffectFn3 a b c r
+
+foreign import mkEffectFn4
+  :: forall a b c d r
+   . (a -> b -> c -> d -> Effect r)
+  -> EffectFn4 a b c d r
+
+foreign import mkEffectFn5
+  :: forall a b c d e r
+   . (a -> b -> c -> d -> e -> Effect r)
+  -> EffectFn5 a b c d e r
+
+foreign import mkEffectFn6
+  :: forall a b c d e f r
+   . (a -> b -> c -> d -> e -> f -> Effect r)
+  -> EffectFn6 a b c d e f r
+
+foreign import mkEffectFn7
+  :: forall a b c d e f g r
+   . (a -> b -> c -> d -> e -> f -> g -> Effect r)
+  -> EffectFn7 a b c d e f g r
+
+foreign import mkEffectFn8
+  :: forall a b c d e f g h r
+   . (a -> b -> c -> d -> e -> f -> g -> h -> Effect r)
+  -> EffectFn8 a b c d e f g h r
+
+foreign import mkEffectFn9
+  :: forall a b c d e f g h i r
+   . (a -> b -> c -> d -> e -> f -> g -> h -> i -> Effect r)
+  -> EffectFn9 a b c d e f g h i r
+
+foreign import mkEffectFn10
+  :: forall a b c d e f g h i j r
+   . (a -> b -> c -> d -> e -> f -> g -> h -> i -> j -> Effect r)
+  -> EffectFn10 a b c d e f g h i j r
+
+foreign import runEffectFn1
+  :: forall a r
+   . EffectFn1 a r
+  -> a
+  -> Effect r
+
+foreign import runEffectFn2
+  :: forall a b r
+   . EffectFn2 a b r
+  -> a
+  -> b
+  -> Effect r
+
+foreign import runEffectFn3
+  :: forall a b c r
+   . EffectFn3 a b c r
+  -> a
+  -> b
+  -> c
+  -> Effect r
+
+foreign import runEffectFn4
+  :: forall a b c d r
+   . EffectFn4 a b c d r
+  -> a
+  -> b
+  -> c
+  -> d
+  -> Effect r
+
+foreign import runEffectFn5
+  :: forall a b c d e r
+   . EffectFn5 a b c d e r
+  -> a
+  -> b
+  -> c
+  -> d
+  -> e
+  -> Effect r
+
+foreign import runEffectFn6
+  :: forall a b c d e f r
+   . EffectFn6 a b c d e f r
+  -> a
+  -> b
+  -> c
+  -> d
+  -> e
+  -> f
+  -> Effect r
+
+foreign import runEffectFn7
+  :: forall a b c d e f g r
+   . EffectFn7 a b c d e f g r
+  -> a
+  -> b
+  -> c
+  -> d
+  -> e
+  -> f
+  -> g
+  -> Effect r
+
+foreign import runEffectFn8
+  :: forall a b c d e f g h r
+   . EffectFn8 a b c d e f g h r
+  -> a
+  -> b
+  -> c
+  -> d
+  -> e
+  -> f
+  -> g
+  -> h
+  -> Effect r
+
+foreign import runEffectFn9
+  :: forall a b c d e f g h i r
+   . EffectFn9 a b c d e f g h i r
+  -> a
+  -> b
+  -> c
+  -> d
+  -> e
+  -> f
+  -> g
+  -> h
+  -> i
+  -> Effect r
+
+foreign import runEffectFn10
+  :: forall a b c d e f g h i j r
+   . EffectFn10 a b c d e f g h i j r
+  -> a
+  -> b
+  -> c
+  -> d
+  -> e
+  -> f
+  -> g
+  -> h
+  -> i
+  -> j
+  -> Effect r
 
 -- The reason these are written eta-expanded instead of as:
 -- ```
@@ -232,28 +381,52 @@ instance semigroupEffectFn2 :: Semigroup r => Semigroup (EffectFn2 a b r) where
   append f1 f2 = mkEffectFn2 \a b -> runEffectFn2 f1 a b <> runEffectFn2 f2 a b
 
 instance semigroupEffectFn3 :: Semigroup r => Semigroup (EffectFn3 a b c r) where
-  append f1 f2 = mkEffectFn3 \a b c -> runEffectFn3 f1 a b c <> runEffectFn3 f2 a b c
+  append f1 f2 = mkEffectFn3 \a b c -> runEffectFn3 f1 a b c <> runEffectFn3 f2
+    a
+    b
+    c
 
 instance semigroupEffectFn4 :: Semigroup r => Semigroup (EffectFn4 a b c d r) where
-  append f1 f2 = mkEffectFn4 \a b c d -> runEffectFn4 f1 a b c d <> runEffectFn4 f2 a b c d
+  append f1 f2 = mkEffectFn4 \a b c d -> runEffectFn4 f1 a b c d <> runEffectFn4
+    f2
+    a
+    b
+    c
+    d
 
 instance semigroupEffectFn5 :: Semigroup r => Semigroup (EffectFn5 a b c d e r) where
-  append f1 f2 = mkEffectFn5 \a b c d e -> runEffectFn5 f1 a b c d e <> runEffectFn5 f2 a b c d e
-
-instance semigroupEffectFn6 :: Semigroup r => Semigroup (EffectFn6 a b c d e f r) where
-  append f1 f2 = mkEffectFn6 \a b c d e f -> runEffectFn6 f1 a b c d e f <> runEffectFn6 f2 a b c d e f
-
-instance semigroupEffectFn7 :: Semigroup r => Semigroup (EffectFn7 a b c d e f g r) where
-  append f1 f2 = mkEffectFn7 \a b c d e f g -> runEffectFn7 f1 a b c d e f g <> runEffectFn7 f2 a b c d e f g
-
-instance semigroupEffectFn8 :: Semigroup r => Semigroup (EffectFn8 a b c d e f g h r) where
-  append f1 f2 = mkEffectFn8 \a b c d e f g h -> runEffectFn8 f1 a b c d e f g h <> runEffectFn8 f2 a b c d e f g h
-
-instance semigroupEffectFn9 :: Semigroup r => Semigroup (EffectFn9 a b c d e f g h i r) where
-  append f1 f2 = mkEffectFn9 \a b c d e f g h i -> runEffectFn9 f1 a b c d e f g h i <> runEffectFn9 f2 a b c d e f g h i
-
-instance semigroupEffectFn10 :: Semigroup r => Semigroup (EffectFn10 a b c d e f g h i j r) where
-  append f1 f2 = mkEffectFn10 \a b c d e f g h i j -> runEffectFn10 f1 a b c d e f g h i j <> runEffectFn10 f2 a b c d e f g h i j
+  append f1 f2 = mkEffectFn5 \a b c d e -> runEffectFn5 f1 a b c d e <>
+    runEffectFn5 f2 a b c d e
+
+instance semigroupEffectFn6 ::
+  Semigroup r =>
+  Semigroup (EffectFn6 a b c d e f r) where
+  append f1 f2 = mkEffectFn6 \a b c d e f -> runEffectFn6 f1 a b c d e f <>
+    runEffectFn6 f2 a b c d e f
+
+instance semigroupEffectFn7 ::
+  Semigroup r =>
+  Semigroup (EffectFn7 a b c d e f g r) where
+  append f1 f2 = mkEffectFn7 \a b c d e f g -> runEffectFn7 f1 a b c d e f g <>
+    runEffectFn7 f2 a b c d e f g
+
+instance semigroupEffectFn8 ::
+  Semigroup r =>
+  Semigroup (EffectFn8 a b c d e f g h r) where
+  append f1 f2 = mkEffectFn8 \a b c d e f g h -> runEffectFn8 f1 a b c d e f g h
+    <> runEffectFn8 f2 a b c d e f g h
+
+instance semigroupEffectFn9 ::
+  Semigroup r =>
+  Semigroup (EffectFn9 a b c d e f g h i r) where
+  append f1 f2 = mkEffectFn9 \a b c d e f g h i ->
+    runEffectFn9 f1 a b c d e f g h i <> runEffectFn9 f2 a b c d e f g h i
+
+instance semigroupEffectFn10 ::
+  Semigroup r =>
+  Semigroup (EffectFn10 a b c d e f g h i j r) where
+  append f1 f2 = mkEffectFn10 \a b c d e f g h i j ->
+    runEffectFn10 f1 a b c d e f g h i j <> runEffectFn10 f2 a b c d e f g h i j
 
 instance monoidEffectFn1 :: Monoid r => Monoid (EffectFn1 a r) where
   mempty = mkEffectFn1 \_ -> mempty
@@ -282,5 +455,7 @@ instance monoidEffectFn8 :: Monoid r => Monoid (EffectFn8 a b c d e f g h r) whe
 instance monoidEffectFn9 :: Monoid r => Monoid (EffectFn9 a b c d e f g h i r) where
   mempty = mkEffectFn9 \_ _ _ _ _ _ _ _ _ -> mempty
 
-instance monoidEffectFn10 :: Monoid r => Monoid (EffectFn10 a b c d e f g h i j r) where
+instance monoidEffectFn10 ::
+  Monoid r =>
+  Monoid (EffectFn10 a b c d e f g h i j r) where
   mempty = mkEffectFn10 \_ _ _ _ _ _ _ _ _ _ -> mempty
diff --git a/test/regression/uncurried.lua b/test/regression/uncurried.lua
index 3e0eb09..0a12ecc 100644
--- a/test/regression/uncurried.lua
+++ b/test/regression/uncurried.lua
@@ -3,12 +3,11 @@
 -- The FFI bound ten curried parameters a..j but called the underlying
 -- function with only nine (a..i), silently dropping j. This loads the
 -- FFI table directly and checks that every argument reaches `fn`.
-
 local M = assert(dofile("src/Effect/Uncurried.lua"))
 
 local seen
 local recorder = function(...)
-  seen = { ... }
+  seen = {...}
   return nil
 end
 
@@ -17,9 +16,6 @@ M.runEffectFn10(recorder)(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)()
 
 assert(seen ~= nil, "fn was never called")
 assert(#seen == 10, "expected 10 forwarded arguments, got " .. #seen)
-for k = 1, 10 do
-  assert(seen[k] == k,
-    "argument #" .. k .. " not forwarded (got " .. tostring(seen[k]) .. ")")
-end
+for k = 1, 10 do assert(seen[k] == k, "argument #" .. k .. " not forwarded (got " .. tostring(seen[k]) .. ")") end
 
 print("OK runEffectFn10 forwards all ten arguments")
diff --git a/treefmt.nix b/treefmt.nix
new file mode 100644
index 0000000..0f57573
--- /dev/null
+++ b/treefmt.nix
@@ -0,0 +1,43 @@
+{ pkgs, ... }:
+{
+  projectRootFile = "flake.nix";
+
+  # Nix — RFC 166 formatter.
+  programs.nixfmt.enable = true;
+
+  # Dhall — spago.dhall / packages.dhall layout.
+  programs.dhall.enable = true;
+
+  # PureScript — purs-tidy is not a first-class treefmt program, so wire it via
+  # the generic mechanism. It picks up `.tidyrc.json` from the project root.
+  settings.formatter.purs-tidy = {
+    command = "${pkgs.purs-tidy}/bin/purs-tidy";
+    options = [ "format-in-place" ];
+    includes = [ "*.purs" ];
+  };
+
+  # Lua FFI — LuaFormatter keeps the parentheses pslua's foreign-file parser
+  # requires (unlike StyLua, which strips them). Config in `.lua-format`.
+  settings.formatter.lua-format = {
+    command = "${pkgs.luaformatter}/bin/lua-format";
+    options = [
+      "-i"
+      "-c"
+      ".lua-format"
+    ];
+    includes = [ "*.lua" ];
+  };
+
+  # Never format generated output or vendored trees.
+  settings.global.excludes = [
+    "dist/*"
+    "output/*"
+    ".spago/*"
+    "node_modules/*"
+    "*.lock"
+    "flake.lock"
+    "spago.lock"
+    ".tidyrc.json"
+    ".lua-format"
+  ];
+}