diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9d90937ca..6d2905e80 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -49,7 +49,7 @@ jobs:
         run: cargo fmt --all -- --check
 
       - name: Clippy
-        run: cargo clippy --all-targets --all-features
+        run: cargo clippy --all-targets --all-features -- -D warnings
 
       - name: Docs
         run: cargo doc --workspace --exclude koto_cli
diff --git a/CHANGELOG.md b/CHANGELOG.md
index b4c10dcc5..392159ea9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,7 +19,9 @@ The Koto project adheres to
     f (10, 100, 1, 2, 3)
     # 1006
     ```
-- Arithmetic-assignment operators (`@+=`, `@*=`, etc.) can now be implemented in meta maps and external values.
+- Meta map improvements
+  - Arithmetic-assignment operators (`@+=`, `@*=`, etc.) can now be implemented in meta maps and external values.
+  - The function call operator (`@||`) can be implemented to values that behave like functions.
 
 #### Internals
 
diff --git a/docs/language/meta_maps.md b/docs/language/meta_maps.md
index 5db308890..af404bc15 100644
--- a/docs/language/meta_maps.md
+++ b/docs/language/meta_maps.md
@@ -86,6 +86,25 @@ print! (foo 10)[7]
 check! 17
 ```
 
+### `@||`
+
+The `@||` meta key defines how the value should behave when called as a
+function.
+
+```koto
+foo = |n|
+  data: n
+  @||: |self| 
+    self.data *= 2
+    self.data
+
+x = foo 2
+print! x()
+check! 4
+print! x()
+check! 8
+```
+
 ### `@iterator`
 
 The `@iterator` meta key defines how iterators should be made when the value is
diff --git a/koto/tests/libs/random.koto b/koto/tests/libs/random.koto
index 5b12089d8..4cbebd48a 100644
--- a/koto/tests/libs/random.koto
+++ b/koto/tests/libs/random.koto
@@ -6,9 +6,8 @@ from test import assert, assert_eq, assert_ne, assert_near
     random.seed 1
 
   @test bool: ||
-    rng_bool = import random.bool
-    assert rng_bool()
-    assert not rng_bool()
+    assert random.bool()
+    assert not random.bool()
 
   @test number: ||
     assert_near random.number(), 0.402, 0.001
@@ -20,7 +19,7 @@ from test import assert, assert_eq, assert_ne, assert_near
 
   @test pick_list: ||
     x = ["foo", "bar", "baz"]
-    assert (x.contains (random.pick x))
+    assert x.contains random.pick x
 
   @test pick_map: ||
     x = {foo: 123, bar: 456, baz: 789}
@@ -29,15 +28,15 @@ from test import assert, assert_eq, assert_ne, assert_near
 
   @test pick_range: ||
     x = 0..10
-    assert (x.contains (random.pick x))
+    assert x.contains random.pick x
 
   @test pick_tuple: ||
     x = ("foo", "bar", "baz")
-    assert (x.contains (random.pick x))
+    assert x.contains random.pick x
 
   @test generator: ||
     get_rng_output = |rng|
-      (0..10)
+      0..10
         .each |_| rng.pick 0..5
         .to_tuple()
 
@@ -47,9 +46,9 @@ from test import assert, assert_eq, assert_ne, assert_near
 
     output1 = get_rng_output rng1
 
-    assert_eq output1, (get_rng_output rng2)
-    assert_ne output1, (get_rng_output rng3)
+    assert_eq output1, get_rng_output rng2
+    assert_ne output1, get_rng_output rng3
 
     # seed can be used to reseed the unique generator
     rng3.seed 0
-    assert_eq output1, (get_rng_output rng3)
+    assert_eq output1, get_rng_output rng3
diff --git a/koto/tests/meta_maps.koto b/koto/tests/meta_maps.koto
index d856a22f9..452c3eabc 100644
--- a/koto/tests/meta_maps.koto
+++ b/koto/tests/meta_maps.koto
@@ -40,15 +40,19 @@ globals.foo_meta =
   @==: |self, other| self.x == other.x
   @!=: |self, other| not self == other
 
-  # Negation
+  # Negation (e.g. -foo)
   @negate: |self| foo -self.x
 
-  # Not
+  # Not (e.g. !foo)
   @not: |self| if self.x == 0 then true else false
 
+  # Function call
+  @||: |self| self.x
+
   # Indexing
   @[]: |self, index| self.x + index
 
+  # Overloaded iteration behaviour
   @iterator: |self| 0..self.x
 
   # Formatting
@@ -136,6 +140,9 @@ globals.foo_meta =
     assert_eq foo(10)[5], 15
     assert_eq foo(100)[-1], 99
 
+  @test call: ||
+    assert_eq foo(99)(), 99
+
   @test iterator: ||
     assert_eq foo(5).to_tuple(), (0, 1, 2, 3, 4)
     assert_eq foo(-4).to_list(), [0, -1, -2, -3]
diff --git a/src/bytecode/src/compiler.rs b/src/bytecode/src/compiler.rs
index dd713a239..963967d7d 100644
--- a/src/bytecode/src/compiler.rs
+++ b/src/bytecode/src/compiler.rs
@@ -431,7 +431,6 @@ impl Compiler {
                 result
             }
             Node::SmallInt(n) => {
-                dbg!(n);
                 let result = self.get_result_register(result_register)?;
                 if let Some(result) = result {
                     match *n {
diff --git a/src/parser/src/node.rs b/src/parser/src/node.rs
index 3ca9866c6..f3820a0b2 100644
--- a/src/parser/src/node.rs
+++ b/src/parser/src/node.rs
@@ -573,6 +573,9 @@ pub enum MetaKeyId {
     /// @type
     Type,
 
+    /// @||
+    Call,
+
     /// @tests
     Tests,
     /// @test test_name
diff --git a/src/parser/src/parser.rs b/src/parser/src/parser.rs
index 76a897ca5..1dc6ee9c7 100644
--- a/src/parser/src/parser.rs
+++ b/src/parser/src/parser.rs
@@ -2042,6 +2042,10 @@ impl<'source> Parser<'source> {
                 Some(Token::SquareClose) => MetaKeyId::Index,
                 _ => return self.error(SyntaxError::UnexpectedMetaKey),
             },
+            Some(Token::Function) => match self.consume_token() {
+                Some(Token::Function) => MetaKeyId::Call,
+                _ => return self.error(SyntaxError::UnexpectedMetaKey),
+            },
             _ => return self.error(SyntaxError::UnexpectedMetaKey),
         };
 
diff --git a/src/runtime/src/meta_map.rs b/src/runtime/src/meta_map.rs
index 1c88e687e..8d74146c7 100644
--- a/src/runtime/src/meta_map.rs
+++ b/src/runtime/src/meta_map.rs
@@ -75,6 +75,10 @@ pub enum MetaKey {
     ///
     /// e.g. `@not`
     UnaryOp(UnaryOp),
+    /// Function call - `@||`
+    ///
+    /// Defines the behaviour when performing a function call on the value.
+    Call,
     /// A named key
     ///
     /// e.g. `@meta my_named_key`
@@ -116,6 +120,7 @@ impl MetaKey {
         match self {
             MetaKey::BinaryOp(op) => MetaKeyRef::BinaryOp(*op),
             MetaKey::UnaryOp(op) => MetaKeyRef::UnaryOp(*op),
+            MetaKey::Call => MetaKeyRef::Call,
             MetaKey::Named(name) => MetaKeyRef::Named(name),
             MetaKey::Test(name) => MetaKeyRef::Test(name),
             MetaKey::Tests => MetaKeyRef::Tests,
@@ -132,6 +137,7 @@ impl fmt::Display for MetaKey {
         match self {
             MetaKey::BinaryOp(op) => write!(f, "@{op}"),
             MetaKey::UnaryOp(op) => write!(f, "@{op}"),
+            MetaKey::Call => f.write_str("@||"),
             MetaKey::Named(name) => write!(f, "{name}"),
             MetaKey::Test(test) => write!(f, "test({test})"),
             MetaKey::Tests => f.write_str("@tests"),
@@ -296,6 +302,7 @@ pub fn meta_id_to_key(id: MetaKeyId, name: Option<ValueString>) -> Result<MetaKe
         MetaKeyId::Negate => MetaKey::UnaryOp(Negate),
         MetaKeyId::Not => MetaKey::UnaryOp(Not),
         MetaKeyId::Display => MetaKey::UnaryOp(Display),
+        MetaKeyId::Call => MetaKey::Call,
         MetaKeyId::Named => {
             MetaKey::Named(name.ok_or_else(|| "Missing name for named meta entry".to_string())?)
         }
@@ -316,6 +323,7 @@ pub fn meta_id_to_key(id: MetaKeyId, name: Option<ValueString>) -> Result<MetaKe
 enum MetaKeyRef<'a> {
     BinaryOp(BinaryOp),
     UnaryOp(UnaryOp),
+    Call,
     Named(&'a str),
     Test(&'a str),
     Tests,
diff --git a/src/runtime/src/value.rs b/src/runtime/src/value.rs
index 9d47bffd9..ca35d0f97 100644
--- a/src/runtime/src/value.rs
+++ b/src/runtime/src/value.rs
@@ -135,7 +135,12 @@ impl Value {
     /// Returns true if the value has function-like callable behaviour
     pub fn is_callable(&self) -> bool {
         use Value::*;
-        matches!(self, SimpleFunction(_) | Function(_) | ExternalFunction(_))
+        match self {
+            SimpleFunction(_) | Function(_) | ExternalFunction(_) => true,
+            Map(m) => m.contains_meta_key(&MetaKey::Call),
+            ExternalValue(v) => v.contains_meta_key(&MetaKey::Call),
+            _ => false,
+        }
     }
 
     /// Returns true if the value doesn't have internal mutability
diff --git a/src/runtime/src/vm.rs b/src/runtime/src/vm.rs
index 774834881..b9e7115aa 100644
--- a/src/runtime/src/vm.rs
+++ b/src/runtime/src/vm.rs
@@ -3045,6 +3045,32 @@ impl Vm {
                 call_arg_count,
                 instance_register,
             ),
+            Map(ref map) if map.contains_meta_key(&MetaKey::Call) => {
+                // Set the map as the instance by placing it in the frame base,
+                // and then passing it into call_callable
+                let instance = function.clone();
+                self.set_register(frame_base, instance);
+                self.call_callable(
+                    result_register,
+                    map.get_meta_value(&MetaKey::Call).unwrap(),
+                    frame_base,
+                    call_arg_count,
+                    Some(frame_base),
+                    temp_tuple_values,
+                )
+            }
+            ExternalValue(ref v) if v.contains_meta_key(&MetaKey::Call) => {
+                let instance = function.clone();
+                self.set_register(frame_base, instance);
+                self.call_callable(
+                    result_register,
+                    v.get_meta_value(&MetaKey::Call).unwrap(),
+                    frame_base,
+                    call_arg_count,
+                    Some(frame_base),
+                    temp_tuple_values,
+                )
+            }
             unexpected => type_error("callable function", &unexpected),
         }
     }
diff --git a/src/runtime/tests/external_value_tests.rs b/src/runtime/tests/external_value_tests.rs
index eb70136a1..6037ab36b 100644
--- a/src/runtime/tests/external_value_tests.rs
+++ b/src/runtime/tests/external_value_tests.rs
@@ -115,6 +115,7 @@ mod external_values {
                 }
                 unexpected => type_error_with_slice("Number", unexpected),
             })
+            .data_fn(MetaKey::Call, |data| Ok(Number(data.x.into())))
             .data_fn("to_number", |data| Ok(Number(data.x.into())))
             .data_fn_mut("invert", |data| {
                 data.x *= -1.0;
@@ -275,6 +276,17 @@ x.to_number()
             test_script_with_external_value(script, 66);
         }
 
+        #[test]
+        fn subtract_assign() {
+            let script = "
+x = make_external 42
+x -= make_external 20
+x -= 2
+x.to_number()
+";
+            test_script_with_external_value(script, 20);
+        }
+
         #[test]
         fn multiply_assign() {
             let script = "
@@ -286,7 +298,27 @@ x.to_number()
             test_script_with_external_value(script, 99);
         }
 
-        // TODO missing tests
+        #[test]
+        fn divide_assign() {
+            let script = "
+x = make_external 99
+x /= make_external 3
+x /= 3
+x.to_number()
+";
+            test_script_with_external_value(script, 11);
+        }
+
+        #[test]
+        fn remainder_assign() {
+            let script = "
+x = make_external 99
+x %= make_external 90
+x %= 5
+x.to_number()
+";
+            test_script_with_external_value(script, 4);
+        }
 
         #[test]
         fn less() {
@@ -320,6 +352,15 @@ x[23]
 ";
             test_script_with_external_value(script, 123);
         }
+
+        #[test]
+        fn call() {
+            let script = "
+x = make_external 256
+x()
+";
+            test_script_with_external_value(script, 256);
+        }
     }
 
     mod temporaries {
diff --git a/src/runtime/tests/vm_tests.rs b/src/runtime/tests/vm_tests.rs
index 22fbb4886..b31d3dc54 100644
--- a/src/runtime/tests/vm_tests.rs
+++ b/src/runtime/tests/vm_tests.rs
@@ -2964,6 +2964,39 @@ foos[0] == foos[1]
         }
     }
 
+    mod overloaded_call {
+        use super::*;
+
+        #[test]
+        fn basic_call() {
+            let script = "
+x = { @||: || 42 }
+x()
+";
+            test_script(script, 42);
+        }
+
+        #[test]
+        fn with_args() {
+            let script = "
+x = { @||: |a, b| a + b }
+x 12, 34
+";
+            test_script(script, 46);
+        }
+
+        #[test]
+        fn instance() {
+            let script = "
+x =
+  data: 99
+  @||: |self, z| self.data * z
+x 10
+";
+            test_script(script, 990);
+        }
+    }
+
     mod named_meta_entries {
         use super::*;